View source for Monarch butterfly

{{Short description|Milkweed butterfly in the family Nymphalidae}}
{{Use mdy dates|date=October 2021}}
{{Use American English|date=October 2021}}
{{Speciesbox
 | image             = Monarch Butterfly Danaus plexippus Male 2664px.jpg
 | image_caption     = Male
 | image2            = Monarch In May.jpg
 | image2_caption    = Female
 | status            = LC
 | status_system     = IUCN3.1
 | status_ref        = <ref>{{cite iucn |author=Walker, A. |author2=Thogmartin, W. E. |author3=Oberhauser, K. S. |author4=Pelton, E. M. |author5=Pleasants, J. M. |date=2022 |title=''Danaus plexippus'' |article-number=e.T159971A806727 |doi=10.2305/IUCN.UK.2022-1.RLTS.T159971A806727.en |access-date=6 December 2022}}</ref> (entire species)
 | status2           = VU
 | status2_system    = IUCN3.1
 | status2_ref       = <ref name="IUCN">{{cite iucn |title=''Migratory Monarch Butterfly'' | url= https://www.iucnredlist.org/species/194052138/246096271}}</ref> (migratory subspecies)
 | taxon             = Danaus plexippus
 | authority         = ([[Carl Linnaeus|Linnaeus]], [[Lepidoptera in the 10th edition of Systema Naturae|1758]])
 | range_map         = MonarchDistribution2-3a.png
 | synonyms          = 
* ''Papilio plexippus'' {{small|Linnaeus, 1758}}
* ''Danaus archippus'' {{small|([[Johan Christian Fabricius|Fabricius]], 1793)}}<ref name="RoyEntSoc"/>
* ''Danaus menippe'' {{small|([[Jacob Hübner|Hübner]], 1816)}}<ref name="Scudder"/>
* ''Anosia plexippus'' {{small|(Moore, 1883)}}<ref>{{cite journal|author=Moore|year=1883|title=''Anosia plexippus''|journal=[[Journal of Zoology|Proceedings of the Zoological Society of London]]|pages=234–235}} (Cited in {{cite book|last1=Scudder|first1=Samuel Hubbard|author-link1=Samuel Hubbard Scudder|last2=Davis|first2=William M.|author-link2=William Morris Davis|last3=Woodworth|first3=Charles W.|author-link3=Charles W. Woodworth|last4=Howard|first4=Leland O.|author-link4=Leland Ossian Howard|last5=Riley|first5=Charles V.|author-link5=Charles Valentine Riley|last6=Williston|first6=Samuel|author-link6=Samuel Wendell Williston|year=1889|title=The Butterflies of the Eastern United States and Canada: With Special Reference to New England: ''Anosia plexippus'' - The Monarch|url=https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t3nw03847&seq=10&view=1up|access-date=December 27, 2023|volume=1|page=[https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t3nw03847&seq=774&view=1up 720]|isbn=978-0-665-26322-4|publisher=The author|location=[[Cambridge, Massachusetts]]|doi=10.5962/bhl.title.9161|doi-access=free|lccn=06021638|oclc=2604754|via=[[HathiTrust|HathiTrust Digital Library]]}})</ref>
}}
[[File:Monarch butterfly male (52341).jpg|thumb|Male ''D. p. plexippus'' on ''[[Tithonia]]'' flower]]
[[File:Monarch (Danaus plexippus plexippus) underside Piedra Herrada.jpg|thumb|''D. p. plexippus''<br />Piedra Herrada, Mexico]]
The '''monarch butterfly''' or simply '''monarch''' ('''''Danaus plexippus''''') is a [[milkweed butterfly]] ([[subfamily]] [[Danainae]]) in the family [[Nymphalidae]].<ref name="Agrawal-2017">{{Cite book|url=https://books.google.com/books?id=PAhpDQAAQBAJ|title=Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution|last=Agrawal|first=Anurag|date=March 7, 2017 |publisher=Princeton University Press|isbn=978-1-4008-8476-6}}</ref> Other common names, depending on region, include '''milkweed''', '''common tiger''', '''wanderer''', and '''black-veined brown'''.<ref name="nic.funet.fi"/> It is among the most familiar of [[List of butterflies of North America|North American butterflies]] and an iconic [[pollinator]],<ref>{{cite web|url=https://www.usda.gov/about-usda/news/blog/conserving-monarch-butterflies-and-their-habitats|title=Conserving Monarch Butterflies and their Habitats|year=2015|publisher=USDA}}</ref> although it is not an especially effective pollinator of [[milkweeds]].<ref>Multiple sources:
* {{Cite journal|last1=Jones|first1=Patricia L.|last2=Agrawal|first2=Anurag A.|date=2016|title=Consequences of toxic secondary compounds in nectar for mutualist bees and antagonist butterflies|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ecy.1483|journal=Ecology|volume=97|issue=10|pages=2570–2579|doi=10.1002/ecy.1483|pmid=27859127|bibcode=2016Ecol...97.2570J |hdl=1813/66741 |issn=1939-9170|hdl-access=free|url-access=subscription}}
* {{Cite journal|last1=MacIvor|first1=James Scott|last2=Roberto|first2=Adriano N.|last3=Sodhi|first3=Darwin S.|last4=Onuferko|first4=Thomas M.|last5=Cadotte|first5=Marc W.|date=2017|title=Honey bees are the dominant diurnal pollinator of native milkweed in a large urban park|journal=Ecology and Evolution|volume=7|issue=20|pages=8456–8462|doi=10.1002/ece3.3394|issn=2045-7758|pmc=5648680|pmid=29075462|bibcode=2017EcoEv...7.8456M }}</ref> Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of {{cvt|8.9–10.2|cm}}.<ref name="Garber" /> A [[Müllerian mimic]], the [[viceroy butterfly]], is similar in color and pattern, but is markedly smaller and has an extra black stripe across each hindwing.

The eastern North American monarch population is notable for its annual southward late-summer/autumn [[instinct]]ive [[Monarch butterfly migration|migration]] from the northern and central United States and southern Canada to [[Florida]] and Mexico.<ref name="Agrawal-2017" /> During the fall migration, monarchs cover thousands of miles, with a corresponding multigenerational return north in spring. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern [[California]], but have been found in [[overwintering]] Mexican sites, as well.<ref name="Groth"/><ref name="JointVenture"/> Non-migratory populations are found further south in the Americas, and in parts of Europe, Oceania, and Southeast Asia.

== Etymology ==
The name "monarch" is believed to have been given in honor of King [[William III of England]], as the butterfly's main color is that of the king's secondary title, [[Prince of Orange]].<ref name="Jean Ruth Adams"/> The monarch was originally described by [[Carl Linnaeus]] in his [[10th edition of Systema Naturae|''Systema Naturae'' of 1758]] and placed in the genus ''[[Papilio]]''.<ref name="Carl Linnaeus"/> In 1780, [[Jan Krzysztof Kluk]] used the monarch as the [[type species]] for a new genus, ''[[Danaus (butterfly)|Danaus]]''. However, many works published between at least 1883 and 1964 identified the species as ''Anosia plexippus'' or ''Anosia archippus''.<ref>Multiple sources:
* {{cite journal|author=Moore|year=1883|title=''Anosia plexippus''|journal=[[Journal of Zoology|Proceedings of the Zoological Society of London]]|pages=234–235}} (Cited in {{cite book|last1=Scudder|first1=Samuel Hubbard|author-link1=Samuel Hubbard Scudder|last2=Davis|first2=William M.|author-link2=William Morris Davis|last3=Woodworth|first3=Charles W.|author-link3=Charles W. Woodworth|last4=Howard|first4=Leland O.|author-link4=Leland Ossian Howard|last5=Riley|first5=Charles V.|author-link5=Charles Valentine Riley|last6=Williston|first6=Samuel|author-link6=Samuel Wendell Williston|year=1889|title=The Butterflies of the Eastern United States and Canada: With Special Reference to New England: ''Anosia plexippus'' - The Monarch|url=https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t3nw03847&seq=10&view=1up|access-date=December 27, 2023|volume=1|page=[https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t3nw03847&seq=774&view=1up 720]|isbn=978-0-665-26322-4|publisher=The author|location=[[Cambridge, Massachusetts]]|doi=10.5962/bhl.title.9161|doi-access=free|lccn=06021638|oclc=2604754|via=[[HathiTrust|HathiTrust Digital Library]]}})
* {{cite journal|last=Scudder|first=Samuel Hubbard|author-link=Samuel Hubbard Scudder|year=1888|title=The Natural History of ''Anosia plexippus'' in New England|journal=[[Psyche (entomology journal)|Psyche: A Journal of Entomology]]|location=[[Cambridge, Massachusetts]]|pages=63–66|url=https://archive.org/details/biostor-173532|access-date=December 26, 2023|via=[[Internet Archive]]}}
* {{cite book|last1=Scudder|first1=Samuel Hubbard|author-link1=Samuel Hubbard Scudder|last2=Davis|first2=William M.|author-link2=William Morris Davis|last3=Woodworth|first3=Charles W.|author-link3=Charles W. Woodworth|last4=Howard|first4=Leland O.|author-link4=Leland Ossian Howard|last5=Riley|first5=Charles V.|author-link5=Charles Valentine Riley|last6=Williston|first6=Samuel|author-link6=Samuel Wendell Williston|year=1889|title=The Butterflies of the Eastern United States and Canada: With Special Reference to New England: ''Anosia plexippus'' - The Monarch|url=https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t3nw03847&seq=10&view=1up|access-date=December 27, 2023|volume=1|pages=[https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t3nw03847&seq=774&view=1up 720-748]|isbn=978-0-665-26322-4|publisher=The author|location=[[Cambridge, Massachusetts]]|doi=10.5962/bhl.title.9161|doi-access=free|lccn=06021638|oclc=2604754|via=[[HathiTrust|HathiTrust Digital Library]]}}
* {{cite journal|last=Scudder|first=Samuel Hubbard|author-link=Samuel Hubbard Scudder|date=July 1893|title=Early appearance of Ansonia plexippus|journal=[[Psyche (entomology journal)|Psyche: A Journal of Entomology]]|publisher=[[Wiley (publisher)|John Wiley & Sons, Inc.]]|volume=6|issue=207|pages=491–492|doi=10.1155/1893/39034|doi-access=free}}
* {{cite book|last=Holland|first=William Jacob|author-link=William Jacob Holland|year=1898|title=The Butterfly Book: A Popular Guide To A Knowledge Of The Butterflies Of North America|pages=[https://www.gutenberg.org/files/41279/41279-h/41279-h.htm#Page_63 63], [https://www.gutenberg.org/files/41279/41279-h/41279-h.htm#Page_81 81]|url=https://www.gutenberg.org/files/41279/41279-h/41279-h.htm|access-date=December 26, 2023|publisher=[[Country Life Press]]|location=[[Garden City, New York]]|via=[[Project Gutenberg]]|quote=Linnæus for a fanciful reason gave this insect the name ''Plexippus''. This is its specific name, by which it is distinguished from all other butterflies. It belongs to the genus ''Anosia''. The genus ''Anosia'' is one of the genera which make up the subfamily of the Euplœinæ. The Euplœinæ belong to the great family of the Nymphalidæ. The Nymphalidæ are a part of the suborder of the Rhopalocera, or true butterflies, one of the two great subdivisions of the order Lepidoptera, belonging to the great class Insecta, the highest class in the subkingdom of the Arthropoda. (page 63)}}
* {{cite journal|last=Moffat|first=J.A.|year=1902|title=''Anosia archippus'' does not hibernate|journal=Report of the Entomological Society of Ontario|publisher=[[Entomological Society of Canada|Entomological Society of Ontario]]|volume=32|pages=78–82}} (Cited in {{cite web|title=Monarch Behavior: Migration|work=Reading Room|url=https://www.monarchwatch.org/read/scientific_biblio.html|publisher=[[Monarch Watch|MonarchWatch.org]]|access-date=October 6, 2025|archive-url=https://web.archive.org/web/20241009074936/https://www.monarchwatch.org/read/scientific_biblio.html|archive-date=October 9, 2024|url-status=live}})
* {{cite journal|last=Dyer|first=Harrison G.|year=1902|title=Family LYMNADIDAE: ANOSIA Hubner|url=https://archive.org/details/bulletinunitedst521902unit/page/33/mode/1up|journal=Bulletin of the United States National Museum|number=52: A List Of North American Lepidoptera And Key To The Literature Of This Order Of Insects|page=33|location=Washington, D.C.|publisher=[[Smithsonian Institution#Publications|Smithsonian Institution Press]]|access-date=October 4, 2025|via=[[Internet Archive]]}}
* {{cite journal|last=Pocock|first=R.I.|date=October 12, 1911|title=The Distastefulness of ''Anosia plexippus''|journal=[[Nature (journal)|Nature]]|id=Letter To The Editor|volume=87|issue=2189|pages=484–485|url=https://www.nature.com/articles/087484d0|doi=10.1038/087484d0|bibcode=1911Natur..87..484P|issn=1476-4687|access-date=October 6, 2025|archive-url=https://web.archive.org/web/20250417114636/https://www.nature.com/articles/087484d0|archive-date=April 17, 2025|url-status=live}}
* {{cite journal|last=Banta|first=A.M.|date=December 21, 1911|journal=[[Nature (journal)|Nature]]|title=The Distastefulness of ''Anosia plexippus''|id=Letter To The Editor|volume=88|issue=2199|page=243|doi=10.1038/088243c0|doi-access=free|bibcode=1911Natur..88..243P |issn=1476-4687}}
* {{cite journal|last=Pocock|first=R.I.|date=December 21, 1911|journal=[[Nature (journal)|Nature]]|title=The Distastefulness of ''Anosia plexippus''|id=Letter To The Editor|volume=88|issue=2199|page=243|doi=10.1038/088243c0|doi-access=free|bibcode=1911Natur..88..243P |issn=1476-4687}}
* {{cite journal|last=Banta|first=A.M.|date=May 9, 1912|title=The Distastefulness of ''Anosia plexippus''|id=Letter To The Editor|journal=[[Nature (journal)|Nature]]|volume=89|issue=2219|pages=242–243|url=https://doi.org/10.1038/089242a0|doi=10.1038/089242a0|issn=1476-4687|bibcode=1912Natur..89..242B |access-date=October 6, 2025|archive-url=https://web.archive.org/web/20250417124819/https://www.nature.com/articles/089242a0|archive-date=April 17, 2025|url-status=live|url-access=subscription}}
* {{cite journal|last=Pocock|first=R.I.|date=May 9, 1912|title=The Distastefulness of ''Anosia plexippus''|id=Letter To The Editor|url=https://www.nature.com/articles/089243a0|journal=[[Nature (journal)|Nature]]|volume=89|issue=2219 |page=243|doi=10.1038/089243a0|bibcode=1912Natur..89..243P|issn=1476-4687|access-date=October 6, 2025|archive-url=https://web.archive.org/web/20250417120324/https://www.nature.com/articles/089243a0|archive-date=April 17, 2025|url-status=live}}
* {{cite journal|last=Webster|first=F.M.|date=December 1912|title=The Migration of ''Anosia plexippus'' FAB|journal=[[The Canadian Entomologist]]|volume=44|issue=12|pages=366–367|doi=10.4039/Ent44366-12|url=https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/migration-of-anosia-plexippus-fab/B33E8E674B124D1EFE0119926D1ED5D7|publisher=[[Entomological Society of Canada]]|via=[[Cambridge University Press]] - May 31, 2012|archive-url=https://web.archive.org/web/20251005061102/https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/migration-of-anosia-plexippus-fab/B33E8E674B124D1EFE0119926D1ED5D7|archive-date=October 5, 2025|url-status=live|access-date=October 5, 2025|url-access=subscription}}
* {{cite journal|last=Webster|first= F.M.|title=Another Migration of ''Anosia plexippus'' FAB|journal=[[The Canadian Entomologist]]|volume=46|issue=3|date=March 1914|page=100|url=https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/another-migration-of-anosia-plexippus-fab/9E733CE16B60E36662285D2BD76F9340|doi=10.4039/Ent46100a-3|publisher=[[Entomological Society of Canada]]|archive-url=https://web.archive.org/web/20250429040931/https://www.cambridge.org/core/journals/canadian-entomologist/arteicle/abs/another-migration-of-anosia-plexippus-fab/9E733CE16B60E36662285D2BD76F9340|archive-date=April 29, 2025|url-status=live|via=[[Cambridge University Press]] - May 31, 2012|access-date=October 5, 2025|url-access=subscription}}
* {{cite journal|last=Webster|first= F.M.|date=December 1915|title=Field Notes and Questions: Migrating Notes on the Milkweed Butterfly, ''Anosia plexippus''|journal=[[The Canadian Entomologist]]|volume=47|issue=12|page=406|url=https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/field-notes-and-questions-migrating-notes-on-the-milkweed-butterfly-anosia-plexippus/51E37B73C47A9B88C7041EF3C799A386|doi=10.4039/Ent47406-12|publisher=[[Entomological Society of Canada]]|archive-url=https://web.archive.org/web/20250429184911/https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/field-notes-and-questions-migrating-notes-on-the-milkweed-butterfly-anosia-plexippus/51E37B73C47A9B88C7041EF3C799A386|archive-date=April 29, 2025|url-status=live|via=[[Cambridge University Press]] - May 31, 2012|access-date=October 6, 2025}}
* {{cite journal|last=Teale|first=Edwin Way|author-link=Edwin Way Teale|date=December 1944|title=Observations on the migration of the monarch butterfly (''Anosia plexippus'')|journal=[[Bulletin of the Brooklyn Entomological Society]]|volume=39|pages=161–163|location=[[Brooklyn|Brooklyn, New York]]|publisher=[[Brooklyn Entomological Society]]|via=[[Biodiversity Heritage Library]]|url=https://www.biodiversitylibrary.org/partpdf/177494|archive-url=https://web.archive.org/web/20250616132501/https://www.biodiversitylibrary.org/partpdf/177494|archive-date=June 16, 2025|url-status=live|access-date=October 6, 2025}}
* {{cite journal|last1=Hirumi|first1=H.|last2=Maramorosch|first2=K.|year=1964|title=Tissue culture of monarch butterfly ''Anosia plexippus''|journal=Contributions from Boyce Thompson Institute|volume=22|pages=259–268}} (Cited in {{cite web|title=Tissue culture of monarch butterfly ''Anosia plexippus''|url=https://monarchnet.org/library/431|publisher=MonarchNet|access-date=October 6, 2025|archive-url=https://web.archive.org/web/20251006092558/https://monarchnet.org/library/431|archive-date=October 6, 2025|url-status=live}})
* {{cite web|last=Heywood|first=Hortense Butler|title=Drawing of wings of Anosia Plexippus|work=Hortense Butler Heywood collection, Iowa State University Library Digital Collections|url=https://n2t.net/ark:/87292/w9r606|publisher=[[Iowa State University#Parks Library|Iowa State University Library]]|access-date=October 6, 2025|archive-url=https://web.archive.org/web/20251006094543/https://digitalcollections.lib.iastate.edu/heywood/items/heywood845.html|archive-date=October 6, 2025|url-status=live}}
* {{cite web|title=Anosia|work=[[Animal Diversity Web]]: Classification|year=2025|url=https://animaldiversity.org/accounts/Anosia/classification/|location=[[Ann Arbor, Michigan]]|publisher=[[University of Michigan]]|access-date=October 6, 2025|archive-url=https://web.archive.org/web/20250622033658/https://animaldiversity.org/accounts/Anosia/classification/|archive-date=June 22, 2025|url-status=live}}</ref> 

In 2005, investigators reported that the [[Monophyly|monophyletic]] genus Danaus s.l. had previously been divided into three [[Subgenus|subgenera]] (Danaus s. s., Salatura, and Anosia). However, based on their own studies, which combined [[mitochondrial DNA]] and [[nuclear DNA]] sequence information with [[Morphology (biology)|morphological]] data, they concluded that the earlier classification was unsustainable and should be abandoned.<ref name=smith>{{cite journal|last1=Smith|first1=David A.S.|last2=Lushai|first2=Gugs|last3=Allen|first3=John A.|date=June 10, 2005|title=A classification of ''Danaus'' butterflies (Lepidoptera: Nymphalidae) based upon data from morphology and DNA|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1096-3642.2005.00169.x|journal=[[Zoological Journal of the Linnean Society]]|volume=144|issue=2|pages=191–212|publisher=[[Oxford University Press]]|location=Oxford, Oxfordshire, England|doi=10.1111/j.1096-3642.2005.00169.x|access-date=October 7, 2025}}</ref>

[[Danaus]] ([[Ancient Greek]] {{wikt-lang|grc|Δαναός}}), a great-grandson of [[Zeus]], was a mythical king in [[Egypt]] or [[Libya]], who founded [[Ancient Argos|Argos]]; [[Plexippus]] ({{lang|grc|Πλήξιππος}}) was one of the 50 sons of [[Aegyptus]], the twin brother of Danaus. In [[Homeric Greek]], his name means "one who urges on horses", i.e., "rider" or "[[chariot]]eer".<ref>{{LSJ|plh/cippos|πλήξιππος|ref}}</ref> In the tenth edition of ''Systema Naturae'', at the bottom of page 467,<ref name="Linnaeus, C. (1758)"/> Linnaeus wrote that the names of the ''Danai festivi'', the division of the genus to which ''Papilio plexippus'' belonged, were derived from the sons of Aegyptus. Linnaeus divided his large genus ''Papilio'', containing all known butterfly species, into what we would now call subgenera. The ''Danai festivi'' formed one of the "subgenera", containing colorful species, as opposed to the ''Danai candidi'', containing species with bright white wings. Linnaeus wrote: "{{lang|la|Danaorum Candidorum nomina a filiabus Danai Aegypti, Festivorum a filiis mutuatus sunt.}}" (English: "The names of the ''Danai candidi'' have been derived from the daughters of Danaus, those of the ''Danai festivi'' from the sons of Aegyptus.").

Robert Michael Pyle suggested ''Danaus'' is a masculinized version of [[Danaë]] (Greek {{wikt-lang|grc|Δανάη}}), Danaus's great-great-granddaughter, to whom Zeus came as a shower of gold, which seemed to him a more appropriate source for the name of this butterfly.<ref>{{cite book |last=Pyle |first=Robert Michael |title=Chasing Monarchs: Migrating with the Butterflies of Passage |url=https://books.google.com/books?id=gO9eXQI0ZxQC&pg=PA148|year=2001 |publisher=Houghton Mifflin Books |isbn=978-0-618-12743-6 |pages=148–149}}</ref>

== Taxonomy ==
[[File:albino monarch butterfly.jpg|thumb|White [[Polymorphism (biology)|morph]] of the monarch in Hawaii called the white monarch]]
[[File:Monarch Butterfly G Barker 2023.ogg|thumb|Monarch butterfly, Ashbury, Sydney, 2023]]
Monarchs belong to the subfamily [[Danainae]] of the family [[Nymphalidae]]. Danainae was formerly considered a separately family [[Danaidae]].<ref name="P.R. Ackery"/> The three species of monarch butterflies are:
* ''D. plexippus'', described by Linnaeus in 1758, is the species known most commonly as the monarch butterfly ranging from North America to northern South America. Its range extends worldwide, including Hawaii, Australia, New Zealand, Spain, and the [[Pacific Islands]].
* ''[[Danaus erippus|D. erippus]]'', the southern monarch, was described by [[Pieter Cramer]] in 1775. This species is found in tropical and subtropical latitudes of South America, mainly in Brazil, Uruguay, Paraguay, Argentina, Bolivia, Chile, and southern Peru. The South American monarch and the North American monarch may have been one species at one time. Some researchers believe the southern monarch separated from the monarch's population some two million years ago, at the end of the [[Pliocene]]. [[Sea level]]s were higher, and the entire [[Amazon River|Amazonas]] lowland was a vast expanse of [[brackish]] swamp that offered limited butterfly habitat.<ref name=smith/>
* ''[[Danaus cleophile|D. cleophile]]'', the Jamaican monarch, described by [[Jean-Baptiste Godart]] in 1819, ranges from [[Jamaica]] to [[Hispaniola]].<ref name="IUCN"/>

Six subspecies and two color morphs of ''D. plexippus'' have been identified:<ref name="nic.funet.fi"/>
* ''D. p. plexippus'' – nominate subspecies, described by Linnaeus in 1758, is the migratory subspecies known from most of North America.
** ''D. p. p.'' "form nivosus", the white monarch commonly found on [[Oahu]], Hawaii, and rarely in other locations.<ref name="Lawrence Gibbs"/>
** ''D. p. p.'' (as yet unnamed) – a color morph lacking some wing vein markings.<ref name="Jacob Groth"/>
* ''D. p. nigrippus'' ([[Richard Haensch]], 1909) – South America - as ''forma'': ''Danais'' {{sic}} ''archippus'' f. ''nigrippus''. Hay-Roe et al. in 2007 identified this taxon as a subspecies<ref name="Hay-Roe, Miriam M. 2007"/><!--Note: "nigrippus" may or may not be an available name depending on the provisions of ICZN Article 45.6-->
* ''D. p. megalippe'' ([[Jacob Hübner]], [1826]) – nonmigratory subspecies, and is found from Florida and [[Georgia (U.S. state)|Georgia]] southwards, throughout the [[Caribbean]] and [[Central America]] to the [[Amazon River]].
* ''D. p. leucogyne'' ([[Arthur Gardiner Butler|Arthur G. Butler]], 1884) − St. Thomas
* ''D. p. portoricensis'' [[Austin Hobart Clark]], 1941 − Puerto Rico
* ''D. p. tobagi'' Austin Hobart Clark, 1941 − Tobago

The population level of the white morph in Oahu is nearing 10%. On other Hawaiian islands, the white morph occurs at a relatively low frequency. White monarchs (''D. p. p.'' "form nivosus") have been found throughout the world, including Australia, New Zealand, Indonesia, and the United States.<ref name="Lawrence Gibbs"/> However, some taxonomists disagree on these classifications.<ref name=smith/><ref name="Hay-Roe, Miriam M. 2007"/>

== Genome ==
The monarch was the first butterfly to have its genome sequenced.<ref name="Xerces Society"/>{{rp|12}} The 273-million-[[base pair]] draft sequence includes a set of 16,866 protein-coding genes. The genome provides researchers insights into migratory behavior, the circadian clock, juvenile hormone pathways, and microRNAs that are differentially expressed between summer and migratory monarchs.<ref>Multiple sources:
* {{cite journal |title=The Monarch Butterfly Genome Yields Insights into Long-Distance Migration |journal=[[Cell (journal)|Cell]] |volume=147 |issue=5 |pages=1171–85 |date=November 2011 |pmid=22118469 |doi=10.1016/j.cell.2011.09.052 |pmc=3225893 |last1=Zhan |first1=Shuai |last2=Merlin |first2=Christine |last3=Boore |first3=Jeffrey{{nbsp}}L. |last4=Reppert |first4=Steven{{nbsp}}M.}} 
* {{cite journal |title=A Genome Befitting a Monarch |journal=Cell |volume=147 |issue=5 |pages=970–2 |date=November 2011 |pmid=22118454 |doi=10.1016/j.cell.2011.11.009|last1=Stensmyr |first1=Marcus{{nbsp}}C. |last2=Hansson |first2=Bill{{nbsp}}S. |s2cid=16035019 |doi-access=free}}
* {{cite news |last=Johnson |first=Carolyn Y. |title=Monarch butterfly genome sequenced |newspaper=Boston Globe |location=Boston, MA |date=November 23, 2011 |url=https://www.boston.com/Boston/whitecoatnotes/2011/11/monarch-butterfly-genome-sequenced/gF1mFBxXCLUOHigi2FOHPM/index.html |access-date=January 9, 2012}}</ref> More recently, the genetic basis of monarch migration and warning coloration has been described.<ref name=Zhan>{{cite journal|last1=Zhan|first1=Shuai|last2=Zhang|first2=Wei|last3=Niitepold|first3=Kristjan|last4=Hsu|first4=Jeremy|last5=Haeger|first5=Juan Fernandez|last6=Zalucki|first6=Myron P.|last7=Altizer|first7=Sonia|last8=de Roode|first8=Jacobus C.|last9=Reppert|first9=Stephen M.|last10=Kronforst|first10=Marcus R.|title=The genetics of Monarch butterfly migration and warning coloration|journal=[[Nature (journal)|Nature]] |date=October 1, 2014 |volume=514|issue=7522|pages=317–321|doi=10.1038/nature13812|pmid=25274300|bibcode=2014Natur.514..317Z|pmc=4331202}}</ref>

No genetic differentiation exists between the migratory populations of eastern and western North America.<ref name="Xerces Society"/>{{rp|16}} Recent research has identified the specific areas in the genome of the monarch that regulate migration. No genetic difference is seen between a migrating and nonmigrating monarch, but the gene is expressed in migrating monarchs, but not expressed in nonmigrating monarchs.<ref name="Jeffrey L 2011"/>

A 2015 publication identified genes from wasp [[bracovirus]]es in the genome of the North American monarch<ref>{{Cite journal|last1=Gasmi|first1=Laila|last2=Boulain|first2=Helene|last3=Gauthier|first3=Jeremy|last4=Hua-Van|first4=Aurelie|last5=Musset|first5=Karine|last6=Jakubowska|first6=Agata K.|last7=Aury|first7=Jean-Marc|last8=Volkoff|first8=Anne-Nathalie|last9=Huguet|first9=Elisabeth|date=September 17, 2015|title=Recurrent Domestication by Lepidoptera of Genes from Their Parasites Mediated by Bracoviruses|journal=[[PLOS Genetics]] |volume=11|issue=9|article-number=e1005470|doi=10.1371/journal.pgen.1005470|pmc=4574769|pmid=26379286 |doi-access=free}}</ref> leading to articles about monarch butterflies being [[genetically modified organism]]s.<ref>Multiple sources:
* {{cite web|url=https://www.newscientist.com/article/dn28190-if-viruses-transfer-wasp-genes-into-butterflies-are-they-gm/|title=If viruses transfer wasp genes into butterflies, are they GM?|last=Le Page|first=Michael|date=September 17, 2015|work=[[New Scientist]]|access-date=July 13, 2016}}
* {{cite web|url=http://europe.newsweek.com/gmo-butterflies-made-naturally-parasitic-wasps-333221?rm=eu|title=Wasps Have Genetically Modified Butterflies, Using Viruses|last=Main|first=Douglas|date=September 17, 2015|work=[[Newsweek]]|access-date=July 13, 2016|archive-date=August 9, 2016|archive-url=https://web.archive.org/web/20160809012925/http://europe.newsweek.com/gmo-butterflies-made-naturally-parasitic-wasps-333221?rm=eu}}</ref>

== Life cycle ==
[[File:Butterfly life cycle diagram in English.svg|right|thumb|upright=1.0|The life cycle of the monarch butterfly]]

Like all Lepidoptera, monarchs undergo complete [[metamorphosis (biology)#Insects|metamorphosis]]; their life cycle has four phases: egg, larva, pupa, and adult. Monarchs transition from eggs to adults during warm summer temperatures in as little as 25 days, extending to as many as seven weeks during cool spring conditions. During their development, both larvae and their milkweed hosts are vulnerable to weather extremes, predators, parasites, and diseases; commonly fewer than 10% of monarch eggs and caterpillars survive.<ref name="Xerces Society"/>{{rp|21–22}}

===Egg===
[[File:Stages_of_Monarch_Development_-_Egg_to_Chrysalis_(28563105684).jpg|thumb|300px|upright|right|Sequential stages of monarch development - an egg, five caterpillars, and a chrysalis on common milkweed leaves]]
[[File:Danaus plexippus, Monarch egg.jpg|thumb|upright|right|Egg]]
[[File:Monarch depositing egg.webm|thumb|thumbtime=125|[[Danaus plexippus|Monarch butterfly]] flying around [[Asclepias fascicularis|narrowleaf milkweed]], depositing an egg. Played a second time at half speed.]]
The egg is derived from materials ingested as a larva and from the [[spermatophore]]s received from males during mating.<ref name=o3>[[#%7B%7Bharvid%7COberhauser2004%7D%7D|Oberhauser (2004)]], p. 3</ref> Female monarchs lay eggs singly, most often on the underside of a young leaf of a milkweed plant during the spring and summer.<ref name="NatGeo"/> Females secrete a small amount of glue to attach their eggs directly to the plant. They typically lay 300 to 500 eggs over a two- to five-week period.<ref>{{cite web|url=https://monarchjointventure.org/monarch-biology/life-cycle/egg|title=Egg|year=2021|publisher=Monarch Joint Venture|access-date=October 6, 2021|archive-url=https://web.archive.org/web/20210711120121/https://monarchjointventure.org/monarch-biology/life-cycle/egg|archive-date=July 11, 2021|url-status=live}}</ref>

Eggs are cream colored or light green, ovate to conical in shape, and about {{cvt|1.2|×|0.9|mm}} in size. The eggs weigh less than {{cvt|0.5|mg}} each and have raised ridges that form longitudinally from the point to apex to the base. Although each egg is {{frac|1|1000}} the mass of the female, she may lay up to her own mass in eggs. Females lay smaller eggs as they age. Larger females lay larger eggs.<ref name=o3/> The number of eggs laid by a female, which may mate several times, can reach 1,180.<ref>{{cite book |last1=Oberhauser |first1=Karen S. |author-link1=Karen Oberhauser |last2=Solensky |first2=Michelle J |title=The Monarch Butterfly: Biology and Conservation |year=2004 |publisher=Cornell University Press |location=Ithaca NY |isbn=978-0-8014-4188-2 |edition=First |ref={{harvid|Oberhauser2004}} |url=https://archive.org/details/monarchbutterfly00mich |page=23}}</ref>

Eggs take three to eight days to develop and hatch into larvae or [[caterpillar]]s.<ref name="Xerces Society"/>{{rp|21}} The offspring's consumption of milkweed benefits health and helps defend them against predators.<ref name="T. Lefevre"/><ref name="Jaap de Roode"/> Monarchs lay eggs along the southern migration route.{{sfn|Oberhauser|2004|p=51}}

===Larva===
[[File:Monarch caterpillar (23229).jpg|thumb|Monarch caterpillar]]
[[File:Swallowtail Caterpillar, Monarch Caterpillar & Queen Caterpillar in Florida (27224446333).jpg|thumb|upright|right|Size comparison between a [[Papilio polyxenes|parsley worm]] (top), a monarch caterpillar (middle), and a [[Queen (butterfly)#Caterpillar|queen caterpillar]] (bottom) all on a human hand]]

The larva (caterpillar) has five stages ([[instar]]s), [[molt]]ing at the end of each instar. Instars last about 3 to 5 days, depending on factors such as temperature and food availability.<ref name="Agrawal-2017" /><ref name=instar>{{cite web|url=https://monarchjointventure.org/monarch-biology/life-cycle/larva/guide-to-monarch-instars|title=Guide to Monarch Instars|year=2021|publisher=Monarch Joint Venture|access-date=October 1, 2021|archive-url=https://web.archive.org/web/20210813231235/https://monarchjointventure.org/monarch-biology/life-cycle/larva/guide-to-monarch-instars|archive-date=August 13, 2021|url-status=live}}</ref>

The first-instar caterpillar that emerges from the egg is pale green or grayish-white, shiny, almost translucent, with a large, black head. It lacks banding coloration or tentacles. The larva or caterpillar eats its egg case and begins to feed on milkweed in a circular motion, often leaving a characteristic, arc-shaped hole in the leaf. Older first-instar larvae have dark stripes on a greenish background and develop small bumps that later become front tentacles. The first instar is usually between {{cvt|2 and 6|mm}} long.<ref name=instar/>

The second-instar larva develops a characteristic pattern of white, yellow, and black transverse bands. The larva has a yellow triangle on the head and two sets of yellow bands around this central triangle. It is no longer translucent and is covered in short [[setae]]. Pairs of black tentacles begin to grow, a larger pair on the thorax and a smaller pair on the abdomen. The second instar is usually between {{cvt|6|mm}} and {{cvt|1|cm}} long.<ref name=instar/>

[[File:Monarch caterpillars.webm|thumb|upright|right|thumbtime=0|Fifth-instar monarch caterpillar eating milkweed leaves (Some at 20 × speed). A second-instar larva grazing on a leaf and cutting through a latex vein.]]
The third-instar larva has more distinct bands and the two pairs of tentacles become longer. Legs on the thorax differentiate into smaller pairs near the head and larger pairs further back. Third-instar larvae usually feed using a cutting motion on leaf edges. The third instar is usually between {{cvt|1 and 1.5|cm}} long.<ref name=instar/> The fourth-instar larva has a different banding pattern. It develops white spots on the [[proleg]]s near its back, and is usually between {{cvt|1.5 and 2.5|cm}} long.<ref name=instar/>

The fifth-instar larva has a more complex banding pattern and white dots on the prolegs, with small front legs very close to the head. Its length ranges from {{cvt|2.5 to 4.5|cm}}.<ref name="Agrawal-2017" /><ref name=instar/>
The larvae typically chew through a latex vein to relieve the pressure and feed above it. Fifth-instar larvae often chew a notch in the [[Petiole (botany)|petiole]] of the leaf they are eating, which relieves the latex pressure and causes the leaf to fall into a vertical position.

As the caterpillar completes its growth, it is {{cvt|4.5|cm}} long (large specimens can reach {{cvt|5|cm}}) and {{cvt|7 to 8|mm}} wide, and weighs about {{cvt|1.5|g}}, compared to the first instar, which is {{cvt|2 to 6|mm}} long and {{cvt|0.5 to 1.5|mm}} wide. Fifth-instar larvae greatly increase in size and weight. They then stop feeding and are often found far from milkweed plants as they seek a site for pupating.<ref name=instar/> A monarch caterpillar can travel up to 10 meters from its milkweed plant to find a safe place to pupate.<ref>{{cite web |title=Frequently Asked Questions |url=https://monarchjointventure.org/faq/egg-larva |website=Monarch Joint Venture |publisher=The Monarch Joint Venture |access-date=2 January 2025}}</ref>

In a laboratory setting, the fourth- and fifth-instar caterpillar stages showed aggressive behavior with lower food availability. Attacked caterpillars were found to be attacked when feeding on milkweed leaves, and the caterpillars attacked when foraging for milkweed.<ref>{{cite journal |last1=Collie |first1=Joseph |last2=Granela |first2=Odelvys |last3=Brown |first3=Elizabeth B. |last4=Keene |first4=Alex C. |title=Aggression Is Induced by Resource Limitation in the Monarch Caterpillar |journal=[[iScience]] |date=November 2020 |volume=23 |issue=12 |article-number=101791 |doi=10.1016/j.isci.2020.101791|pmid=33376972 |pmc=7756136 |bibcode=2020iSci...23j1791C |doi-access=free}}</ref> This demonstrates the aggressive behavior of monarch caterpillars due to the availability of milkweed.

===Pupa===
[[File:From a caterpillar to a chrysalis….jpg|thumb|A caterpillar [[Metamorphosis|metamorphosing]] into a pupa]]
[[File:Monarch Butterfly Cocoon 3.jpg|thumb|upright=0.9|Chrysalis|263x263px]]
To prepare for the pupal or [[chrysalis]] stage, the caterpillar chooses a safe place for pupation, where it spins a silk pad on a downward-facing horizontal surface. At this point, it turns around and securely latches on with its last pair of hind legs and hangs upside down, in the form of the letter J. After "J-hanging" for about 12–16 hours, it soon straightens out its body and goes into [[peristalsis]] some seconds before its skin splits behind its head. It then sheds its skin over a few minutes, revealing a green chrysalis (video: https://www.youtube.com/watch?v=QLQmrIUILzc). At first, the chrysalis is long, soft, and somewhat amorphous, but over a few hours, it compacts into its distinct shape – an opaque, pale-green chrysalis with small golden dots near the bottom, and a gold-and-black rim around the dorsal side near the top.<ref>{{Cite journal|last=Petersen|first=B.|date=1964|title=Humidity, Darkness, and Gold Spots as Possible Factors in Pupal Duration of Monarch Butterflies|journal=[[Journal of the Lepidopterists' Society]]|volume=18|pages=230–232}}</ref> At first, its exoskeleton is soft and fragile, but it hardens and becomes more durable within about a day. At this point, it is about {{cvt|2.5|cm}} long and {{cvt|10–12|mm}} wide, weighing about {{cvt|1.2|g}}. At normal summer temperatures, it matures in 8–15 days (usually 11–12 days). During this pupal stage, the adult butterfly forms inside. A day or so before emerging, the exoskeleton first becomes translucent and the chrysalis more bluish. Finally, within 12 hours or so, it becomes transparent, revealing the black and orange colors of the butterfly inside before it [[Eclosion|ecloses]] (emerges).<ref>Multiple sources:
* {{cite web|url=https://monarchjointventure.org/monarch-biology/life-cycle/pupa|title=Pupa|year=2021|publisher=Monarch Joint Venture|access-date=October 5, 2021|archive-url=https://web.archive.org/web/20210711050853/https://monarchjointventure.org/monarch-biology/life-cycle/pupa|archive-date=July 11, 2021}}
* {{Cite journal|last1=Pocius|first1=V. M.|last2=Debinski|first2=D. M.|last3=Pleasants|first3=J. M.|last4=Bidne|first4=K. G.|last5=Hellmich|first5=R. L.|last6=Brower|first6=L. P.|date=2017-09-07|title=Milkweed Matters: Monarch Butterfly (Lepidoptera: Nymphalidae) Survival and Development on Nine Midwestern Milkweed Species|journal=[[Environmental Entomology]]|volume=46|issue=5|pages=1098–1105|doi=10.1093/ee/nvx137|pmid=28961914|pmc=5850784|issn=0046-225X|doi-access=free}}</ref>

In 2009, monarchs were reared on the [[International Space Station]], successfully emerging from pupae located in the station's Commercial Generic Bioprocessing Apparatus.<ref>Multiple sources:
* {{cite web|url=https://www.nasa.gov/mission_pages/station/expeditions/expedition22/butterflies.html|archive-url=https://web.archive.org/web/20091215044602/http://www.nasa.gov/mission_pages/station/expeditions/expedition22/butterflies.html|archive-date=December 15, 2009|title=Butterflies Emerge from Cocoons Aboard Station|year=2009|publisher=NASA}}
* {{cite web|url=https://www.nbcnews.com/id/wbna34349127|title=First Monarch butterflies in space take flight|work=[[NBC News]]|date=December 9, 2009|access-date=November 12, 2023}}</ref>

===Adult===

[[File:Danaus plexippus emerging from chrysalis 04.jpg|thumb|upright=0.9|right|An emergent monarch clinging to its chrysalis shell]]
The adult emerges from its chrysalis after about two weeks of pupation (video: https://www.youtube.com/watch?v=tQDGizDHVs8 ). The emergent adult hangs upside down for several hours while it pumps fluids and air into its wings, which expand, dry, and stiffen. The butterfly then extends and retracts its wings. Once conditions allow, it flies and feeds on many nectar plants. During the breeding season, adults reach sexual maturity in 4–5 days. However, the migrating generation does not reach maturity until overwintering is complete.<ref name="monarchlab.org"/>
[[File:Monarchs flying and sipping.webm|thumb|upright=0.9|right|Monarch butterflies flying and sipping [[nectar]] from milkweed flowers]]

The adult's wingspan ranges from {{convert|8.9|to|10.2|cm}}.<ref name="Garber"/> The upper sides of the [[Insect wing|wings]] are tawny orange, the veins and margins are black, and two series of small white spots occur in the margins. Monarch forewings also have a few orange spots near their tips. Wing undersides are similar, but the tips of forewings and hindwings are yellow-brown instead of tawny orange and the white spots are larger.<ref name=Braby/> The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants.<ref name="Satterfield"/> Wings size and shape differ between migratory and nonmigratory monarchs. Monarchs from eastern North America have larger and more angular forewings than the western population.<ref name="Xerces Society"/>

In eastern North American populations, overall wing size in the physical dimensions of wings varies. Males tend to have larger wings than females and are typically heavier than females. Both males and females have similar thoracic dimensions. Female monarchs tended to have thicker wings, which are thought to convey greater tensile strength and reduce the likelihood of being damaged during migration. Additionally, females had lower [[wing loading]] than males, meaning females require less energy to fly.<ref>{{cite journal|last1=Davis|first1=A. K.|last2=Holden|first2= Michael T.|year=2015|url=http://downloads.hindawi.com/archive/2015/591705.pdf|title=Measuring Intraspecific Variation in Flight-Related Morphology of Monarch Butterflies (''Danaus plexippus''): Which Sex Has the Best Flying Gear?|journal=Journal of Insects |volume=2015|issue=59170|pages=1–6|publisher=Hindawi Publishing Corporation|doi=10.1155/2015/591705|access-date=October 17, 2020|doi-access=free}}</ref>

Adults are [[sexual dimorphism|sexually dimorphic]]. Males are slightly larger than females and have a black spot on a vein on each hindwing. The spots contain androconial scales that produce [[pheromone]]s that many Lepidoptera use during courtship. Females are often darker than males and have wider veins on their wings. The ends of the abdomens of males and females differ in shape.<ref name="Xerces Society"/><ref name=Braby/><ref name="ref1"/><ref>Multiple sources:
* {{cite web|url=https://monarchjointventure.org/monarch-biology/life-cycle/adult|title=Adult|year=2021|publisher=Monarch Joint Venture|access-date=October 5, 2021|archive-url=https://web.archive.org/web/20210721001949/https://monarchjointventure.org/monarch-biology/life-cycle/adult|archive-date=July 21, 2021}}
* {{cite web|url=https://www.monarchwatch.org/biology/sense1.htm|title=Sensory Systems|work=Biology|publisher=[[Monarch Watch]]|access-date=October 5, 2021|archive-url=https://web.archive.org/web/20180319015951/https://www.monarchwatch.org/biology/sense1.htm|archive-date=March 19, 2018|url-status=live}}
* {{cite web|url=https://www.monarchwatch.org/biology/sexing.htm|title=Sexing Monarchs|work=Biology|publisher=[[Monarch Watch]]|access-date=October 5, 2021|archive-url=https://web.archive.org/web/20210505140543/https://www.monarchwatch.org/biology/sexing.htm|archive-date=May 5, 2021|url-status=live}}</ref>

The adult [[thorax]] has six legs, but like all Nymphalidae, the forelegs are small and held against the body. The butterfly uses only its middle and hind legs when walking and clinging.<ref name="Gene Darby"/>

Adults typically live for 2–5 weeks during their breeding season.<ref name="Xerces Society"/>{{rp|22–23}} Larvae growing in high densities are smaller, have lower survival, and weigh less as adults compared with those growing in lower densities.<ref name="D.T. Flockhart"/>

=== Male ===
Male monarch butterflies can be distinguished from females by the small, black, fuzzy spots on their hind wings, which are scent glands used for courtship, and by their slightly thinner black wing veins.<ref>{{Cite web |title=Monarch Butterfly {{!}} Species {{!}} WWF |url=https://www.worldwildlife.org/species/monarch-butterfly |access-date=2025-09-02 |website=World Wildlife Fund |language=en-US}}</ref>

=== Female ===
Female monarch butterflies lack these spots, have a more orange-brown appearance, and generally have thicker, wider black wing veins than males.
Key Differences 

* '''Wing Spots:''' The most reliable way to tell them apart is by looking for a small, black, fuzzy spot on the inner surface of the hind wings. This spot is present on all male monarch butterflies but is absent in females.<ref name=":0">{{Cite web |title=Monarch Watch: Size and Mass |url=https://monarchwatch.org/class/size-mass.html |access-date=2025-09-02 |website=monarchwatch.org}}</ref>
* '''Wing Veins:''' Female monarchs typically have thicker, wider black veins on their wings compared to males.<ref name=":0" />
* '''Color:''' While both are bright orange, females tend to have a darker, more orange-brown appearance, and their coloring can be described as having a more robust and darker orange.<ref name=":0" /> 
* '''Size:''' Males are generally slightly larger than females, although this is not always noticeable and may vary with genetics and nutrition.<ref name=":0" />
* '''Body:''' Both sexes have a black body with white markings.<ref name=":0" />

== Vision ==
Physiological experiments suggest that monarch butterflies view the world through a tetrachromatic system.<ref name="Blackiston-2011">{{Cite journal|last1=Blackiston|first1=Douglas|last2=Briscoe|first2=Adriana D.|last3=Weiss|first3=Martha R.|date=February 1, 2011 |title=Color vision and learning in the monarch butterfly, ''Danaus plexippus'' (Nymphalidae)|journal=[[The Journal of Experimental Biology]]|volume=214|issue=Pt 3|pages=509–520|doi=10.1242/jeb.048728|issn=1477-9145|pmid=21228210|doi-access=free|bibcode=2011JExpB.214..509B }}</ref> Like [[human]]s, their [[retina]] contain three types of opsin proteins, expressed in distinct photoreceptor cells, each of which absorbs light at a different wavelength. Unlike humans, one of those types of photoreceptor cells corresponds to a wavelength in the [[ultraviolet]] range; the other two correspond to blue and green.<ref>{{Cite journal|last1=Stalleicken|first1=Julia|last2=Labhart|first2=Thomas|last3=Mouritsen|first3=Henrik|date=March 2006|title=Physiological characterization of the compound eye in monarch butterflies with focus on the dorsal rim area|journal=[[Journal of Comparative Physiology A]] |volume=192 |issue=3 |pages=321–331 |doi=10.1007/s00359-005-0073-6 |issn=0340-7594 |pmid=16317560|s2cid=31493135}}</ref>

In addition to these three photoreceptor cells in the main retina, monarch butterfly eyes contain orange filtering pigments that filter the light reaching some green-absorbing opsins, thereby making a fourth photoreceptor cell sensitive to longer-wavelength light.<ref name="Blackiston-2011" /> The combination of filtered and unfiltered green opsins allows the butterflies to distinguish yellow from orange colors.<ref name="Blackiston-2011" /> The ultraviolet opsin protein has also been detected in the dorsal rim region of monarch eyes. One study suggests that this allows the butterflies to detect ultraviolet-polarized skylight to orient themselves with the sun for their long [[Insect migration|migratory]] flight.<ref>{{Cite journal |last1=Sauman |first1=Ivo |last2=Briscoe |first2=Adriana D. |last3=Zhu |first3=Haisun |last4=Shi |first4=Dingding |last5=Froy |first5=Oren |last6=Stalleicken |first6=Julia |last7=Yuan |first7=Quan |last8=Casselman |first8=Amy |last9=Reppert |first9=Steven M. |date=May 5, 2005 |title=Connecting the Navigational Clock to Sun Compass Input in Monarch Butterfly Brain|journal=[[Neuron (journal)|Neuron]] |volume=46 |issue=3 |pages=457–467 |doi=10.1016/j.neuron.2005.03.014 |pmid=15882645|s2cid=17755509 |issn=0896-6273 |doi-access=free}}</ref>

These butterflies are capable of distinguishing colors based on their wavelength only, and not based on intensity; this phenomenon is termed "true color vision". This is important for many butterfly behaviors, including seeking nectar for nourishment, choosing a mate, and finding milkweed on which to lay eggs. One study found that floral color is more easily recognized at a distance by butterflies searching for nectar than floral shape. This may be because flowers have highly contrasting colors to the green background of a vegetative landscape.<ref name="Cepero-2015" /> Leaf shape is important for oviposition so that the butterflies can ensure their eggs are laid on milkweed.

Beyond the perception of color, the ability to remember certain colors is essential in the life of monarch butterflies. These insects can easily learn to associate color, and to a lesser extent, shape, with sugary food rewards. When searching for [[nectar]], color is the first cue that draws the insect's attention toward a potential food source, and shape is a secondary characteristic that promotes the process. When searching for a place to lay its eggs, the roles of color and shape are switched. Also, a difference may exist between male and female butterflies from other species regarding the ability to learn certain colors; however, no differences are noted between the sexes for monarch butterflies.<ref name="Cepero-2015">{{Cite journal|last1=Cepero|first1=Laurel C.|last2=Rosenwald|first2=Laura C.|last3=Weiss|first3=Martha R.|date=July 1, 2015 |title=The Relative Importance of Flower Color and Shape for the Foraging Monarch Butterfly (Lepidoptera: Nymphalidae)|journal=Journal of Insect Behavior|volume=28|issue=4|pages=499–511|doi=10.1007/s10905-015-9519-z|bibcode=2015JIBeh..28..499C |s2cid=18380612|issn=1572-8889}}</ref>

==Courtship and mating==
[[File:Monarch butterfly mating.webm|thumb|Monarch butterflies mating (video)]]

Monarch courtship occurs in two phases. During the aerial phase, a male pursues and often forces a female to the ground. During the ground phase, the butterflies copulate and remain attached for about 30 to 60 minutes.<ref name="Emmel, Thomas C."/> Only 30% of mating attempts end in copulation, suggesting that females can avoid mating, though some have more success than others.<ref name="Oberhauser-2004"/><ref name="Frey-1998"/> During copulation, a male transfers his [[spermatophore]] to a female. Along with [[sperm]], the spermatophore provides a female with nutrition, which aids her in laying eggs. An increase in spermatophore size increases the fecundity of female monarchs. Males that produce larger spermatophores also fertilize more females' eggs.<ref name="Oberhauser-2009"/>

Females and males typically mate more than once. Females that mate several times lay more eggs.<ref name="Oberhauser-1989"/> Mating for the overwintering populations occurs in the spring, before dispersion. Mating is less dependent on pheromones than in other species in its genus.<ref name="animaldiversity1"/> Male search and capture strategies may influence copulatory success, and human-induced changes to the habitat can influence monarch mating activity at overwintering sites.<ref>{{Cite journal|last=Solensky|first=Michelle J.|date=November 2004|title=The Effect of Behavior and Ecology on Male Mating Success in Overwintering Monarch Butterflies (''Danaus plexippus'')|journal=Journal of Insect Behavior |volume=17 |issue=6 |pages=723–743 |doi=10.1023/b:joir.0000048985.58159.0d |bibcode=2004JIBeh..17..723S |s2cid=31954178|issn=0892-7553}}</ref>

==Distribution and habitat==
[[File:String of Monarchs, Pismo Preserve.jpg|thumb|upright=1.5|String of monarchs wintering at California's [[Pismo State Beach]] Monarch Preserve (2015)]]
The range of the western and eastern populations of ''D. p. plexippus'' expands and contracts depending upon the season. The range differs between breeding areas, migration routes, and winter roosts.<ref name="Xerces Society"/>{{rp|18}} However, no genetic differences between the western and eastern monarch populations exist;<ref name="Jeffrey L 2011"/> reproductive isolation has not led to subspeciation of these populations, as it has elsewhere within the species' range.<ref name="Xerces Society"/>{{rp|19}}

In the Americas, the monarch ranges from southern Canada through northern South America.<ref name="Agrawal-2017" /> It is also found in [[Bermuda]], the [[Cook Islands]],<ref name="Gerald McCormack"/> Hawaii,<ref name=jas/><ref name="Lincoln P. Brower"/> Cuba,<ref name="Donald Davis"/> and other Caribbean islands,<ref name="Xerces Society"/>{{rp|18}} the [[Solomon Islands|Solomons]], [[New Caledonia]], New Zealand,<ref name="monarch.org.nz"/> [[Papua New Guinea]],<ref name="NewsAdvance.com"/> Australia, the [[Azores]], the [[Canary Islands]], [[Madeira]], continental Portugal, [[Gibraltar]],<ref>{{cite web|url=http://www.gonhs.org/LepidopteraofGibraltar.htm|title=Provisional species list of the Lepidoptera|publisher=Gibraltar Ornithological and Natural History Society|archive-url=https://web.archive.org/web/20150925111106/http://www.gonhs.org/LepidopteraofGibraltar.htm |archive-date=September 25, 2015|url-status=live}}</ref> the Philippines, and [[Morocco]].<ref name="Miguel Pais"/> It appears in the UK in some years as an accidental migrant.<ref name="Simon Coombes"/>

Overwintering populations of ''D. p. plexippus'' are found in Mexico, California, along the [[Gulf Coast of the United States]], year-round in Florida, and in Arizona where the habitat has the specific conditions necessary for survival.<ref name=rcgt>Cech, Rick and Tudor, Guy (2005). ''Butterflies of the East Coast''. Princeton University Press, Princeton, NJ. {{ISBN|0-691-09055-6}}</ref><ref name=isc>Iftner, David C.; Shuey, John A. and Calhoun, John C. (1992). ''Butterflies and Skippers of Ohio''. College of Biological Sciences and The Ohio State University. {{ISBN|0-86727-107-8}}</ref> On the [[East Coast of the United States]], they have overwintered as far north as [[Virginia Beach, Virginia]].<ref>{{cite web |title=Monarch Butterfly Journey North |url=https://journeynorth.org/tm/monarch/TagRecoveryVAWinter2006.html |access-date=July 16, 2017 |publisher=University of Wisconsin-Madison Arboretum}}</ref> Their wintering habitat typically provides access to streams, plenty of sunlight (enabling body temperatures that allow flight), and appropriate roosting vegetation, and is relatively free of predators.

Overwintering, roosting butterflies have been seen on basswoods, elms, sumacs, locusts, oaks, osage-oranges, mulberries, pecans, willows, cottonwoods, and mesquites.<ref name="Robert Michael Pyle"/> While breeding, monarch habitats can be found in agricultural fields, pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides – anywhere there is access to larval host plants.<ref name="Sue Halpern"/>

== Larval host plants ==
[[File:Asclepias syriacus.tif|thumb|right|220px|''[[Asclepias syriaca]]'', common milkweed]]
[[File:Asclepias curassavica-Thekkady-2016-12-03-001.jpg|thumb|right|220px|''[[Asclepias curassavica]]'', tropical milkweed]]
The host plants used by the monarch caterpillar include:
{{div col|colwidth=13em}}
* ''[[Araujia sericifera]]'' – white bladderflower<ref>Multiple sources:
* {{cite web|url=https://plants.ces.ncsu.edu/plants/araujia-sericifera/|title=''Araujia sericifera''|work=Plant Toolbox|publisher=North Carolina Cooperative Extension|access-date=March 8, 2024|archive-url=https://web.archive.org/web/20240207064303/https://plants.ces.ncsu.edu/plants/araujia-sericifera/|archive-date=February 7, 2024|url-status=live}}
* {{cite journal|last1=Wise|first1=K. A. J.|author-link1=Keith Arthur John Wise|date=June 1963|url=https://nzetc.victoria.ac.nz/tm/scholarly/tei-Bio11Tuat02-t1-body-d5.html|title=Food-Plants of 'Monarch' Butterfly Larvae|journal=Tuatara|volume=11|number=2|pages=81–82|location=[[Wellington|Wellington, New Zealand]]|publisher=[[Victoria University of Wellington]]|access-date=March 7, 2024|archive-url=https://web.archive.org/web/20231130120728/https://nzetc.victoria.ac.nz/tm/scholarly/tei-Bio11Tuat02-t1-body-d5.html|archive-date=November 30, 2023|url-status=live}}</ref>
* ''[[Asclepias angustifolia]]'' – Arizona milkweed<ref name="Monarch Joint Venture">{{cite web|title=Plant Milkweed for Monarchs|url=https://www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf|publisher=[[United States Forest Service]]|access-date=March 1, 2024|archive-url=https://web.archive.org/web/20240115183150/https://www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf|archive-date=January 15, 2024|url-status=live}}</ref>
* ''[[Asclepias albicans]]'' – whitestem milkweed<ref>Multiple sources:
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=ASAL|title=''Asclepias albicans''|work=Plant Database: [[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=May 31, 2023|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20230328084838/https://www.wildflower.org/plants/result.php?id_plant=ASAL|archive-date=March 28, 2023|url-status=live}}
* {{cite web|url=http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250131177|title=Asclepias albicans|work=[[Flora of North America]]|publisher=eFloras.org|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20240117180059/http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250131177|archive-date=January 17, 2024|url-status=live}}</ref>
* ''[[Asclepias asperula]]'' – antelope horns milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias californica]]'' – California milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias cordifolia]]'' – heartleaf milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias curassavica]]'' – tropical milkweed<ref>Multiple sources:
* {{cite web|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276911|title=''Asclepias curassavica''|work=Plant Finder|location=[[St. Louis]]|publisher=[[Missouri Botanical Garden]]|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20220519222723/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276911|archive-date=May 19, 2022|url-status=live}}
* {{cite web|url=https://plants.ces.ncsu.edu/plants/asclepias-curassavica/|title=''Asclepias curassavica''|work=Plant Toolbox|publisher=North Carolina Cooperative Extension|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20240112182659/https://plants.ces.ncsu.edu/plants/asclepias-curassavica/|archive-date=January 12, 2024|url-status=live}}</ref>
* ''[[Asclepias eriocarpa]]'' – woollypod milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias erosa]]'' – desert milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias exaltata]]'' – poke milkweed<ref name="Monarch Joint Venture"/><ref>Multiple sources:
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=asex|title=''Asclepias exaltata''|work=Plant Database: [[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=August 5, 2016|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20240111121310/https://www.wildflower.org/plants/result.php?id_plant=asex|archive-date=January 11, 2024|url-status=live}}
* {{cite web|url=https://plants.ces.ncsu.edu/plants/asclepias-exaltata/|title=''Asclepias exaltata''|work=Plant Toolbox|publisher=North Carolina Cooperative Extension|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20230922192205/https://plants.ces.ncsu.edu/plants/asclepias-exaltata/|archive-date=September 22, 2023|url-status=live}}
* {{cite web|url=https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-exaltata/|title=''Asclepias exaltata'', (Poke Milkweed)|work=Bring Back The Monarchs|publisher=[[Monarch Watch]]|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20231004074622/https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-exaltata/|archive-date=October 4, 2023|url-status=live}}</ref>
* ''[[Asclepias fascicularis]]'' – Mexican whorled milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias hirtella]]'' – tall green milkweed<ref>Multiple sources:
* {{cite web|url=https://www.illinoiswildflowers.info/prairie/plantx/tg_milkweed.htm|title=Tall Green Milkweed: ''Asclepias hirtella''|work=Illinois Wildflowers|access-date=January 15, 2024|archive-url=https://web.archive.org/web/20100326094201/https://www.illinoiswildflowers.info/prairie/plantx/tg_milkweed.htm|archive-date=March 26, 2010|url-status=live}}
* {{PLANTS|id=ASHI|taxon=Asclepias hirtella|accessdate=13 February 2018}}</ref>
* ''[[Asclepias humistrata]]'' – sandhill/pinewoods milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias incarnata]]'' – swamp milkweed<ref>Multiple sources:
* {{cite web|last1=Kirk|first1=S.|last2=Belt|first2=S.|url=https://plants.sc.egov.usda.gov/DocumentLibrary/factsheet/pdf/fs_asin.pdf|title=Plant fact sheet for swamp milkweed (''Asclepias incarnata'')|location=[[Beltsville, Maryland]]|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]: Norman A. Berg National Plant Materials Center|access-date=July 9, 2021|archive-url=https://web.archive.org/web/20210709171300/https://plants.sc.egov.usda.gov/DocumentLibrary/factsheet/pdf/fs_asin.pdf|archive-date=July 9, 2021|url-status=live}}
* {{cite web|first=Forest Russell|last=Holmes|url=https://www.fs.fed.us/wildflowers/plant-of-the-week/asclepias_incarnata.shtml|title=Swamp Milkweed (''Asclepias incarnata'' L.)|work=Plant of the Week|location=Washington, D.C.|publisher=[[United States Department of Agriculture]]: [[United States Forest Service]]|access-date=July 9, 2021|archive-url=https://web.archive.org/web/20210328183622/https://www.fs.fed.us/wildflowers/plant-of-the-week/asclepias_incarnata.shtml|archive-date=March 28, 2021|url-status=live}}
* {{cite web|title=Plant Milkweed for Monarchs|url=https://www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf|publisher=[[United States Forest Service]]|access-date=March 1, 2024|archive-url=https://web.archive.org/web/20240115183150/https://www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf|archive-date=January 15, 2024|url-status=live}}</ref>
* ''[[Asclepias lanceolata]]'' – fewflower milkweed<ref>Multiple sources:
* {{cite web|title=''Asclepias lanceolata'' Walt.|url=http://www.wildflower.org/plants/result.php?id_plant=ASLA2|work=Plant Database: [[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=October 10, 2013|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20230930235552/http://www.wildflower.org/plants/result.php?id_plant=ASLA2|archive-date=September 30, 2023|url-status=live}}
* {{cite web|url=https://plants.ces.ncsu.edu/plants/asclepias-lanceolata/|title=''Asclepias lanceolata''|work=Plant Toolbox|publisher=North Carolina Cooperative Extension|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20230923210241/https://plants.ces.ncsu.edu/plants/asclepias-lanceolata/|archive-date=September 23, 2023|url-status=live}}</ref>
* ''[[Asclepias linaria]]'' – pineneedle milkweed<ref>Multiple sources
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=ASLI6|title=''Asclepias linaria'' Cav.|work=Plant Database: [[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=November 12, 2014|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20220122134832/https://www.wildflower.org/plants/result.php?id_plant=ASLI6|archive-date=January 22, 2022|url-status=live}}
* {{cite web|url=https://horticultureunlimited.com/plant-guide/threadleaf-milkweed/|title=Threadleaf Milkweed: ''Asclepias linaria''|year=2024|location=[[Tucson, Arizona]]|publisher=Horticulture Unlimited, Inc.|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20211017144800/https://horticultureunlimited.com/plant-guide/threadleaf-milkweed/|archive-date=October 17, 2021|url-status=live}}
* {{cite web|url=http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250131175|title=Asclepias linaria|work=[[Flora of North America]]|publisher=eFloras.org|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20240117182125/http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250131175|archive-date=January 17, 2024|url-status=live}}</ref>
* ''[[Asclepias meadii]]'' – Meade's milkweed<ref>Multiple sources:
* {{cite web|last=Betz|first=R. F.|url=http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC11/reference/econatres.napc11.rbetz2.pdf|editor1-last=Bragg|editor1-first=Thomas B.|editor2-last=Stubbendieck|editor2-first=James|year=1989|title=Ecology of Mead's milkweed (''Asclepias meadii'' Torrey)|work=Prairie pioneers: ecology, history and culture: proceedings of the Eleventh North American Prairie Conference held 7–11 August 1988|location=[[Lincoln, Nebraska]]|publisher=[[University of Nebraska–Lincoln|University of Nebraska]] Printing|pages=187–191|oclc=741871225|access-date=March 10, 2024|archive-url=https://web.archive.org/web/20221016033416/http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC11/reference/econatres.napc11.rbetz2.pdf|archive-date=October 16, 2022|url-status=live|via=[[University of Wisconsin-Madison#Libraries|University of Wisconsin-Madison Libraries]]}}
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=ASME|title=''Asclepias meadii''|work=Plant Database: [[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=November 12, 2014|access-date=March 10, 2024|archive-url=https://web.archive.org/web/20210121053124/https://www.wildflower.org/plants/result.php?id_plant=ASME|archive-date=January 21, 2021|url-status=live}}
* {{cite web|url=https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.129673/Asclepias_meadii|title=''Asclepias meadii'': Meade's Milkweed|work=NatureServe Explorer|location=[[Arlington County, Virginia]]|publisher=[[NatureServe]]|access-date=January 17, 2024|archive-date=January 24, 2022|archive-url=https://web.archive.org/web/20220124230304/https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.129673/Asclepias_meadii|url-status=live}}
* {{cite web|url=https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-meadii/|title=''Asclepias meadii'', (Mead's milkweed)|work=Bring Back The Monarchs|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20220927115639/https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-meadii/|archive-date=September 27, 2022|url-status=live|publisher=[[Monarch Watch]]}}</ref>
* ''[[Asclepias nivea]]'' – Caribbean milkweed<ref>{{cite web|archive-url=https://web.archive.org/web/20150707204139/https://sites.google.com/site/gardeningforbutterflies/asclepias-nivea|archive-date=July 7, 2015|url=https://sites.google.com/site/gardeningforbutterflies/asclepias-nivea|title=''Asclepias nivea''|work=Butterfly gardening & all things milkweed|access-date=July 7, 2015}}</ref>
* ''[[Asclepias oenotheroide]]'' – zizotes milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias perennis]]'' – aquatic milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias quadrifolia]]'' –  four-leaved milkweed<ref>Multiple sources:
* {{cite web |title=Four-leaved milkweed |date=July 17, 2014 |url=https://www.ontario.ca/page/four-leaved-milkweed|publisher=[[Ontario]], Canada|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20230523124302/https://www.ontario.ca/page/four-leaved-milkweed|archive-date=May 23, 2023|url-status=live}}
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=asqu|title=''Asclepias quadrifolia''|work=Plant Database: [[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=May 4, 2022|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20230923042933/https://www.wildflower.org/plants/result.php?id_plant=asqu|archive-date=September 23, 2023|url-status=live}}
* {{cite web|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276922|title=''Asclepias quadrifolia''|work=Plant Finder|location=[[St. Louis]]|publisher=[[Missouri Botanical Garden]]|access-date=January 17, 2024|archive-url=https://web.archive.org/web/20220506231630/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276922|archive-date=May 6, 2022|url-status=live}}</ref>
* ''[[Asclepias rubra]]'' — red milkweed<ref>{{cite web|date=November 2, 2014|first=Joseph A.|last=Marcus|title=''Asclepias rubra'' (Red milkweed)|url=https://www.wildflower.org/plants/result.php?id_plant=asru|work=Plant Database|publisher=[[Lady Bird Johnson Wildflower Center]] at the [[University of Texas at Austin]]|access-date=December 24, 2025|archive-url=https://web.archive.org/web/20250218195920/https://www.wildflower.org/plants/result.php?id_plant=asru|archive-date=February 18, 2025|url-status=live}}</ref>
* ''[[Asclepias speciosa]]'' – showy milkweed<ref name="Monarch Joint Venture"/><ref>Multiple sources:
* {{cite web|first=Michelle|last=Stevens|date=May 30, 2006|url=https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assp.pdf|title=Plant guide for ''Asclepias speciosa''|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]|access-date=July 12, 2021|archive-url=https://web.archive.org/web/20210712172322/https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assp.pdf|archive-date=July 12, 2021|url-status=live}}
* {{cite web|last1=Young-Mathews|first1=A.|last2= Eldredge|first2=E.|year=2012|url=https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/orpmcfs11338.pdf|title=Plant fact sheet for showy milkweed (''Asclepias speciosa'')|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]], Corvallis Plant Materials Center, Oregon, and Great Basin Plant Materials Center, [[Fallon, Nevada]]|access-date=July 12, 2021|archive-url=https://web.archive.org/web/20210401052315/https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/orpmcfs11338.pdf|archive-date=April 1, 2021}}
* {{cite web|url=https://www.fs.fed.us/database/feis/plants/forb/ascspe/all.html|title=''Asclepias speciosa''|location=Washington, D.C.|publisher=[[United States Department of Agriculture]]: [[United States Forest Service]]|access-date=July 12, 2021|archive-url=https://web.archive.org/web/20210307062424/https://www.fs.fed.us/database/feis/plants/forb/ascspe/all.html|archive-date=March 7, 2021|url-status=live}}
* {{cite book|first=Karen|last=Wiese|year=2000|chapter-url=https://archive.org/details/sierranevadawild00wies/page/50/mode/2up?q=Asclepias+speciosa|chapter=Showy Milkweed: ''Asclepias speciosa''|url=https://archive.org/details/sierranevadawild00wies/page/n1/mode/2up|title=Sierra Nevada Wildflowers: A Field Guide to Common Wildflowers and Shrubs of the Sierra Nevada, Including Yosemite, Sequoia, and Kings Canyon National Parks|page=50|isbn=0-585-36283-1|oclc=47011272|lccn=00022385|location=[[Helena, Montana]]|publisher=Falcon Publishing, Inc.|via=[[Internet Archive]]|access-date=July 12, 2021}}</ref>
* ''[[Asclepias subulata]]'' – rush milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias sullivantii]]'' – prairie milkweed<ref>Multiple sources:
* {{cite web|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=j450|title=''Asclepias sullivantii''|work=Plant Finder|location=[[St. Louis]]|publisher=[[Missouri Botanical Garden]]|access-date=January 15, 2024|archive-url=https://web.archive.org/web/20230529193523/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx|archive-date=May 29, 2023|url-status=live}}
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=ASSU3|title=''Asclepias sullivantii''|work=[[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=November 2, 2014|access-date=January 15, 2024|archive-url=https://web.archive.org/web/20230329064726/https://www.wildflower.org/plants/result.php?id_plant=ASSU3|archive-date=March 29, 2023|url-status=live}}
* {{cite web|last1=Penskar|first1=M.R.|last2=Higman|first2=P.J|year=2000|url=https://mnfi.anr.msu.edu/abstracts/botany/Asclepias_sullivantii.pdf|title=''Asclepias sullivantii'' Engelm.: Sullivant's milkweed|work=Michigan Natural Features Inventory|location=[[Lansing, Michigan]]|publisher=[[Michigan State University|Michigan State University Extension]]|access-date=January 15, 2024|archive-url=https://web.archive.org/web/20120905160208/https://mnfi.anr.msu.edu/abstracts/botany/Asclepias_sullivantii.pdf|archive-date=September 5, 2012|url-status=live}}</ref>
* ''[[Asclepias syriaca]]'' – common milkweed<ref name="Common Milkweed">Multiple sources:
* {{cite web|first=Michelle|last=Stevens|url=https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf|title=Plant guide for common milkweed (''Asclepias syriaca'')|location=Washington, D.C.|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]: National Plant Data Center|access-date=July 5, 2021|archive-url=https://web.archive.org/web/20210705151637/https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf|archive-date=July 5, 2021|url-status=live}} 
* {{cite web|last=Taylor|first=David|title=Common Milkweed (''Asclepias syriaca'' L.)|work=Plant of the Week|url=https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_syriaca.shtml|access-date=December 24, 2023|archive-url=https://web.archive.org/web/20230122001337/https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_syriaca.shtml|archive-date=January 22, 2023|url-status=live|publisher=[[United States Department of Agriculture]], [[United States Forest Service]]}}
* {{cite news|first=Adrian|last=Higgins|url=http://www.washingtonpost.com/lifestyle/home/creating-a-rest-stop-for-the-monarch/2015/05/26/cd81a75c-ffcb-11e4-805c-c3f407e5a9e9_story.html|title=A gardener's guide to saving the monarch|department=Home & Garden|newspaper=[[The Washington Post]]|date=May 27, 2015|access-date=October 17, 2020|archive-url=https://web.archive.org/web/20200926094219/http://www.washingtonpost.com/lifestyle/home/creating-a-rest-stop-for-the-monarch/2015/05/26/cd81a75c-ffcb-11e4-805c-c3f407e5a9e9_story.html|archive-date=September 26, 2020|url-status=live}}
* {{cite news|first=Adrian|last=Higgins|url=https://www.washingtonpost.com/lifestyle/home/a-world-of-milkweeds/2015/05/26/43fba7d6-fe6c-11e4-833c-a2de05b6b2a4_story.html|title=7 milkweed varieties and where to find them|department=Home & Garden|newspaper=The Washington Post|date=May 27, 2015|access-date=October 17, 2020|archive-url=https://web.archive.org/web/20200926092547/https://www.washingtonpost.com/lifestyle/home/a-world-of-milkweeds/2015/05/26/43fba7d6-fe6c-11e4-833c-a2de05b6b2a4_story.html|archive-date=September 26, 2020|url-status=live}}
* {{cite web|first=Tony|last=Gomez|url=https://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-syriaca/|title=''Asclepias syriaca'': Common Milkweed for Monarch Caterpillars|work=Monarch Butterfly Garden|date=March 14, 2013 |publisher=MonarchButterflyGarden.net|access-date=July 5, 2021|archive-url=https://web.archive.org/web/20150316044421/http://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-syriaca/|archive-date=March 16, 2015|url-status=live}}
* {{cite web|url=https://sites.google.com/site/gardeningforbutterflies/asclepias-syriaca|title=''Asclepias syriaca''|work=Butterfly gardening & all things milkweed|access-date=July 7, 2015|archive-url=https://web.archive.org/web/20150707205734/https://sites.google.com/site/gardeningforbutterflies/asclepias-syriaca|archive-date=July 7, 2015}}
* {{cite web|url=https://www.wildflower.org/plants/result.php?id_plant=ASSY|title=Asclepias syriaca|work=[[Lady Bird Johnson Wildflower Center]]|location=[[Austin, Texas]]|publisher=[[University of Texas at Austin]]|date=August 9, 2020|access-date=January 15, 2024|archive-url=https://web.archive.org/web/20240302013236/https://www.wildflower.org/plants/result.php?id_plant=ASSY|archive-date=March 2, 2024|url-status=live}}
* {{cite web|url=https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-syriaca/|title=''Asclepias syriaca'', (Common Milkweed)|work=Bring Back The Monarchs|publisher=[[Monarch Watch]]|access-date=March 10, 2024|archive-url=https://web.archive.org/web/20231208065758/https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-syriaca/|archive-date=December 8, 2023|url-status=live}}
* {{cite web|title=Plant Milkweed for Monarchs|url=https://www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf|publisher=[[United States Forest Service]]|access-date=March 1, 2024|archive-url=https://web.archive.org/web/20240115183150/https://www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf|archive-date=January 15, 2024|url-status=live}}</ref>
* ''[[Asclepias tuberosa]]'' – butterfly weed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias variegata]]'' – white milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias verticillata]]'' – whorled milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias vestita]]'' – woolly milkweed<ref name="Monarch Joint Venture"/>
* ''[[Asclepias viridis]]'' – green antelopehorn milkweed<ref name="Monarch Joint Venture"/><ref>Multiple sources:
* {{cite web |last=Davis|first=Lee|date=May 31, 2006|url=https://plants.usda.gov/DocumentLibrary/plantguide/pdf/pg_asvi2.pdf|title=Plant guide for Green Milkweed: ''Asclepias viridis'' Walt.|location=Washington, D.C.|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]|access-date=July 11, 2021|archive-url=https://web.archive.org/web/20210711221812/https://plants.usda.gov/DocumentLibrary/plantguide/pdf/pg_asvi2.pdf|archive-date=July 11, 2021|url-status=live}}
* {{cite web|first=David|last=Taylor|url=https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_viridis.shtml|title=Green Antelopehorn (''Asclepias viridis'')|work=Plant of the Week|location=Washington, D.C.|publisher=[[United States Department of Agriculture]]: [[United States Forest Service]]|access-date=July 11, 2021|archive-url=https://web.archive.org/web/20210327062846/https://www.fs.fed.us/wildflowers/plant-of-the-week/asclepias_viridis.shtml|archive-date=March 27, 2021|url-status=live}}
* {{cite book|last9=The Xerces Society for Invertebrate Conservation|author-link9=
Xerces Society|first1=Brianna |last1=Borders|first2=Allen |last2=Casey|first3=John M. |last3=Row|first4=Rich |last4= Wynia|first5=Randy |last5=King|first6=Alayna |last6=Jacobs|first7=Chip |last7=Taylor|first8=Eric |last8=Mader|editor-first1=Hailey |editor-last1=Walls|editor-first2=Kaitlyn |editor-last2=Rich|date=June 24, 2013|url=https://xerces.org/sites/default/files/2018-05/13-037_01_XercesSoc_NativeMilkweeds_Central-US_web.pdf|title=Pollinator Plants of the Central United States: Native Milkweeds (''Asclepias'' spp.)|chapter=''Asclepias viridis'' Green antelopehorn|location=[[Portland, Oregon]]|publisher=[[Xerces Society|The Xerces Society for Invertebrate Conservation]]|access-date=January 24, 2024|archive-url=https://web.archive.org/web/20201106072554/https://xerces.org/sites/default/files/2018-05/13-037_01_XercesSoc_NativeMilkweeds_Central-US_web.pdf|archive-date=November 6, 2020|url-status=live}}
* {{cite web|url=http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Asclepias+viridis|title=''Asclepias viridis'': Spider Milkweed|website=NatureServe|access-date=July 11, 2021|archive-url=https://web.archive.org/web/20150919170036/http://explorer.natureserve.org/servlet/NatureServe?searchName=Asclepias+viridis|archive-date=September 19, 2015|url-status=live}}</ref>
* ''[[Calotropis gigantea]]'' – crown flower<ref>{{cite web|url=http://butterflysocietyofhawaii.org/hawaiis-butterflies/ |title=Butterfly Society of Hawaii |publisher=Butterfly Society of Hawaii |access-date=January 6, 2017}}</ref>
* ''[[Calotropis procera]]'' – giant milkweed<ref>Multiple sources:
* {{cite web|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276915&isprofile=0&|title=''Calotropis procera''|work=Plant Finder|location=[[St. Louis]]|publisher=[[Missouri Botanical Garden]]|access-date=February 3, 2024|archive-url=https://web.archive.org/web/20221126162856/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276915&isprofile=0&|archive-date=November 26, 2022|url-status=live}}
*{{cite web|url=https://www.nrcs.usda.gov/sites/default/files/2022-10/Not%20All%20Monarchs%20Migrate-Puerto%20Rican%20Subspecies%20Stays%20Put.pdf|title=Not All Monarchs Migrate! The Puerto Rican Subspecies Stays Put|date=June 23, 2016|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]|access-date=February 2, 2024|archive-url=https://web.archive.org/web/20230608174451/https://www.nrcs.usda.gov/sites/default/files/2022-10/Not%20All%20Monarchs%20Migrate-Puerto%20Rican%20Subspecies%20Stays%20Put.pdf|archive-date=June 8, 2023|url-status=live|quote=The Puerto Rican monarch's primary host plants are red milkweed (''Asclepias curassavica''), which is native to North and South America, and giant milkweed (''Calotropis procera''), which is native to Europe.}}</ref>
* ''[[Cynanchum angustifolium]]'' – Gulf coast swallow-wort<ref>{{cite web |url=https://www.deweesislandblog.com/2014/09/15/swallow-wort-a-vine-to-watch-for/ |title=Swallow-wort, Cynanchum angustifolium |date=14 November 2025}}</ref>
* ''[[Cynanchum laeve]]'' – sand vine milkweed<ref>Multiple sources:
* {{cite web|first= Jeff|last=Hansen|date=December 24, 2024|title=Butterfly Gardening|work=Kansas Native Plants|url=http://www.kansasnativeplants.com/butterfly.html|location=Topeka, Kansas|publisher=Jeff D. Hansen|access-date=August 14, 2025|archive-url=https://web.archive.org/web/20120224070215/http://www.kansasnativeplants.com/butterfly.html|archive-date=February 24, 2012|url-status=live}}
* {{cite web|title=''Cynanchum laeve''|date=October 6, 2022|work=Plant Database|url=https://www.wildflower.org/plants/result.php?id_plant=CYLA|publisher=[[Lady Bird Johnson Wildflower Center]], [[The University of Texas at Austin]]|access-date=August 14, 2025|archive-url=https://web.archive.org/web/20231205120128/https://www.wildflower.org/plants/result.php?id_plant=CYLA|archive-date=December 5, 2023|url-status=live}}
* {{cite web|title=''Cynanchum laeve'': Climbing Milkweed|url=http://www.missouriplants.com/Cynanchum_laeve_page.html|publisher=missouriplants.com (members of Missouri Native Plant Society)|access-date=August 14, 2025|archive-url=https://web.archive.org/web/20250729042617/http://www.missouriplants.com/Cynanchum_laeve_page.html|archive-date=July 29, 2025|url-status=live}}</ref>
* ''[[Gomphocarpus fruticosus]]'' – swan plant<ref>Multiple sources:
* {{cite journal|last1=Wise|first1=K. A. J.|author-link1=Keith Arthur John Wise|date=June 1963|url=https://nzetc.victoria.ac.nz/tm/scholarly/tei-Bio11Tuat02-t1-body-d5.html|title=Food-Plants of 'Monarch' Butterfly Larvae|journal=Tuatara|volume=11|number=2|pages=81–82|location=[[Wellington|Wellington, New Zealand]]|publisher=[[Victoria University of Wellington]]|access-date=March 7, 2024|archive-url=https://web.archive.org/web/20231130120728/https://nzetc.victoria.ac.nz/tm/scholarly/tei-Bio11Tuat02-t1-body-d5.html|archive-date=November 30, 2023|url-status=live}}
* {{cite web|url=https://weedsofmelbourne.org/narrow-leaved-cotton-bush-gomphocarpus-fruticosus|title=Narrow-leaved Cotton Bush (''Gomphocarpus fruticosus''|work=Weeds of Melbourne|date= March 30, 2021|access-date=March 7, 2024|archive-url=https://web.archive.org/web/20230929004235/https://weedsofmelbourne.org/narrow-leaved-cotton-bush-gomphocarpus-fruticosus|archive-date=September 29, 2023|url-status=live}}</ref>
* ''[[Gomphocarpus physocarpus]]'' – balloon plant<ref>Multiple sources:
* {{cite web|last1=Mahr|first1=Susan|title=Balloon Plant, Gomphocarpus physocarpus |url=https://hort.extension.wisc.edu/articles/balloon-plant-gomphocarpus-physocarpus/ |work=Wisconsin Horticulture: Division of Extension|location=[[Madison, Wisconsin]]|publisher=[[University of Wisconsin–Madison]]|access-date=March 2, 2024|archive-url=https://web.archive.org/web/20231016114309/https://hort.extension.wisc.edu/articles/balloon-plant-gomphocarpus-physocarpus/|archive-date=October 16, 2023|url-status=live}}
* {{cite web|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276871|title=''Gomphocarpus physocarpus''|work=Plant Finder|location=[[St. Louis]]|publisher=[[Missouri Botanical Garden]]|access-date=March 2, 2024|archive-url=https://web.archive.org/web/20240302083100/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276871|archive-date=March 2, 2024|url-status=live}}
* {{cite web|url=https://plants.ces.ncsu.edu/plants/gomphocarpus-physocarpa/|title=''Gomphocarpus physocarpa''|work=Plant Toolbox|publisher=North Carolina Cooperative Extension|access-date=March 2, 2024|archive-url=https://web.archive.org/web/20221130174746/https://plants.ces.ncsu.edu/plants/gomphocarpus-physocarpa/|archive-date=November 30, 2022|url-status=live}}
* {{cite web|url=https://www.gardenia.net/plant/asclepias-physocarpus|title=Asclepias physocarpus (Ballon Plant)|publisher=Gardenia|access-date=March 2, 2022|archive-url=https://web.archive.org/web/20220516185358/https://www.gardenia.net/plant/asclepias-physocarpus|archive-date=May 16, 2022|url-status=live}}</ref>
* ''[[Sarcostemma clausa]]'' – white vine<ref name=jas/><ref name=dlw/>
{{div col end}} 
The eastern monarch migration largely depends upon only three of these species: ''Asclepias syriaca'', ''A. viridis'', and ''A. asperula''.<ref name=Taylor1>{{cite web|first=Chip|last=Taylor|date=March 29, 2024|url=https://monarchwatch.org/blog/2024/03/29/is-the-eastern-monarch-population-continuing-to-decline/|title=Is the eastern monarch population continuing to decline?: Milkweed and monarchs|work=Monarch Watch Blog|publisher=[[Monarch Watch|MonarchWatch.org]]|access-date=September 8, 2024|archive-url=https://web.archive.org/web/20240716153838/https://monarchwatch.org/blog/2024/03/29/is-the-eastern-monarch-population-continuing-to-decline/|archive-date=July 16, 2024|url-status=live}}</ref> Using [[cardenolide]] fingerprinting analysis, investigators have found that 85-92% of monarchs overwintering in Mexico had fed on ''A. syriaca'' as caterpillars.<ref>{{cite book|last1=Borders|first1=B.|last2=Lee-Mäder|first2=E.|chapter=Chapter 2. Milkweed Biology & Ecology|title=Milkweeds: A Conservation Practitioner's Guide |date=2014|page=8 |publisher=[[The Xerces Society for Invertebrate Conservation]]|location=Portland, OR|url=https://xerces.org/sites/default/files/2018-05/17-031_02_XercesSoc_Milkweeds-Conservation-Guide_web.pdf|access-date=July 27, 2025|archive-url=https://web.archive.org/web/20250627171819/https://xerces.org/sites/default/files/2018-05/17-031_02_XercesSoc_Milkweeds-Conservation-Guide_web.pdf|archive-date=June 27, 2025|url-status=live}}</ref>

However, ''Asclepias curassavica'', or tropical milkweed, is often planted as an ornamental in butterfly gardens. Year-round plantings in the USA are controversial and criticized, as they may cause new overwintering sites along the U.S. Gulf Coast, leading to year-round breeding of monarchs.<ref>{{cite journal|doi=10.1155/2010/689301|title=Citizen Science Observations of Monarch Butterfly Overwintering in the Southern United States|journal=[[Psyche (entomology journal)|Psyche: A Journal of Entomology]] |volume=2010 |page=1 |year=2010 |last1=Howard |first1=Elizabeth |last2=Aschen|first2=Harlen |last3=Davis |first3=Andrew K. |doi-access=free}}</ref> This is thought to adversely affect migration patterns and to cause a dramatic buildup of the dangerous parasite, ''[[Ophryocystis elektroscirrha]]''.<ref>{{cite journal |pmid=25589600|pmc=4308991|year=2015|last1=Satterfield|first1=D. A.|title=Loss of migratory behaviour increases infection risk for a butterfly host|journal=[[Proceedings of the Royal Society B: Biological Sciences]]|volume=282|issue=1801|article-number=20141734|last2=Maerz|first2=J. C.|last3=Altizer|first3=S|doi=10.1098/rspb.2014.1734}}</ref> New research also has shown that monarch larvae reared on tropical milkweed show reduced migratory development (reproductive diapause), and when migratory adults are exposed to tropical milkweed, it stimulates reproductive tissue growth.<ref>{{cite journal|title=Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies|journal=[[Insects (journal)|Insects]]|volume=10|number=8|page=253|first1=Ania A. |last1=Majewska|first2=Sonia|last2=Altizer|doi=10.3390/insects10080253|date=August 16, 2019 |pmc=6724006|pmid=31426310|doi-access=free}}</ref>

== Adult food sources ==

[[File:Danaus plexippus on flowers (48483505276).jpg|thumb|right|upright=0.9|Nectaring on Mexican sunflower (''[[Tithonia rotundifolia]]'')]]
Although larvae eat only milkweed, adult monarchs feed on the nectar of many plants, including:<ref>{{cite web|url=https://www.monarchwatch.org/garden/plant-list-monarchwatch.pdf|title=Nectar Plants for Butterflies & Other Pollinators|work=Plants for Butterfly and Pollinator Gardens: Native and Non-native Plants Suitable for Gardens in the Northeastern United States|publisher=[[Monarch Watch]]|access-date=October 1, 2021|archive-url=https://web.archive.org/web/20201112041606/https://www.monarchwatch.org/garden/plant-list-monarchwatch.pdf|archive-date=November 12, 2020|url-status=live}}</ref>

{{div col|colwidth=13em}}
* ''[[Apocynum cannabinum]]'' – Indian hemp
* ''[[Asclepias]]'' spp. – milkweed
* ''[[Buddleja davidii]]'' - butterfly-bush<ref>Multiple sources:
* {{cite web|first=Lynn|last=Kimmerle|date=March 27, 2018|url=http://monarchbookreviews.blogspot.com|title=Monarch butterfly feeding on a Buddleja flower|format=photograph|access-date=September 9, 2024|archive-url=https://web.archive.org/web/20231123131652/https://monarchbookreviews.blogspot.com/|archive-date=November 23, 2023|url-status=live}}
* {{cite web|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=271488&isprofile=1&basic=buddleja%20davidii|title=Buddleja davidii|work=Plant Finder|location=[[St. Louis]]|publisher=[[Missouri Botanical Garden]]|access-date=September 9, 2024|archive-url=https://web.archive.org/web/20231203050441/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=271488&isprofile=1&basic=buddleja%20davidii|archive-date=December 3, 2023|url-status=live|quote=Flowers (each to ½” long) are mildly fragrant, and, as the common name suggests, very attractive to butterflies.}}</ref> 
* ''[[Cirsium]]'' sp. – thistle
* ''[[Daucus carota]]'' – wild carrot
* ''[[Dipsacus sylvestris]]'' – teasel
* ''[[Echinacea]]'' sp. – coneflower
* ''[[Erigeron canadensis]]'' – horseweed
* ''[[Eupatorium maculatum]]'' – spotted Joe-Pye weed
* ''[[Eupatorium perfoliatum]]'' – common boneset
* ''[[Hesperis matronalis]]'' – dame's rocket
* ''[[Liatris]]'' sp. – blazing stars
* ''[[Medicago sativa]]'' – alfalfa
* ''[[Solidago]]'' sp. – goldenrod
* ''[[Symphyotrichum]]'' sp. – New World aster
* ''[[Syringa vulgaris]]'' – lilac
* ''[[Tithonia rotundifolia]]'' – Mexican sunflower<ref name=sunflower>Multiple sources:
* {{cite book|first=Geyata|last=Ajilvsgi|date=June 3, 2013|title=Butterfly Gardening for Texas|page=141|url=https://www.tamupress.com/book/9781603448062/butterfly-gardening-for-texas/|isbn=9781603449571|oclc=841909864|lccn=2012031589|location=[[College Station, Texas]]|publisher=[[Texas A&M University Press]]|quote=During the breeding season, the Monarch's favorite habitats are open fields, meadows, and flower gardens. .... In the fall, it seems especially fond of .... Mexican Sunflower (''Tithonia rotundifolia''), .... .|access-date=November 29, 2025|archive-url=https://web.archive.org/web/20250216130328/https://www.tamupress.com/book/9781603448062/butterfly-gardening-for-texas/|archive-date=February 16, 2025|url-status=live}}
* {{cite web|title=Mexican Sunflower Seeds - (Tithonia rotundifolia 'Torch')|year=2025|url=https://store.underwoodgardens.com/Mexican-Sunflower-Tithonia-rotundifolia-Torch/productinfo/F1095/|location=[[Chino Valley, Arizona]]|publisher=Terroir Seeds|access-date=December 5, 2025|archive-url=https://web.archive.org/web/20250720153729/https://store.underwoodgardens.com/Mexican-Sunflower-Tithonia-rotundifolia-Torch/productinfo/F1095/|archive-date=July 20, 2025|url-status=live|quote=Butterflies of all kinds, but especially the endangered Monarchs, carry a “Torch” for the Mexican sunflower. Swarms of migrating Monarchs are commonly seen mobbing the big, bold, red-orange dahlia-like blooms.}}
* {{cite web|last=Gomez|first=Tony|title=Mexican sunflower: Monarch Butterflies Hold a 'Torch' for Tithonia: Tithonia rotundifolia 'torch'|date=June 5, 2013 |url=https://monarchbutterflygarden.net/butterfly-plants/mexican-sunflower/|location=[[Anoka, Minnesota]]|publisher=Monarch Butterfly Garden|access-date=November 28, 2025|archive-url=https://web.archive.org/web/20250218162757/https://monarchbutterflygarden.net/butterfly-plants/mexican-sunflower/|archive-date=February 18, 2025|url-status=live|quote=Attracts swarms of migrating monarchs. .... The ‘Torch’ cultivar has been widely reported by butterfly gardeners to attract lots of butterflies, but some of the lesser planted varieties might bring home the butterflies too.}}
* {{cite web|first=Karuna|last=Eberl|date=September 5, 2024|title=Grow Mexican Sunflower in Pollinator Gardens|work=Birds&Blooms|url=https://www.birdsandblooms.com/gardening/flower-gardening/mexican-sunflower/|publisher=RDA Enthusiast Brands, LLC|access-date=December 2, 2025|archive-url=https://web.archive.org/web/20250922023452/https://www.birdsandblooms.com/gardening/flower-gardening/mexican-sunflower/|archive-date=September 22, 2025|url-status=live|quote=The blooms of Mexican sunflowers range from red and orange to yellow, with fuzzy stalks that branch out in a big, gangly bunch. They resemble native prairie sunflowers and zinnia more than common sunflowers. Native to Central America and Mexico, they are hearty in arid regions, plus grow quickly into full, lush landscapes with an abundance of flower heads. “That makes them a nectar buffet for swallowtails, monarchs and other butterflies,” says Keri Wilson, a horticulturist with Garden Media Group. “Tithonia also thrives in heat, blooming even when other flowers start to wilt and fade, making it an excellent late-season food source for migrating butterflies."}}</ref><ref>{{cite web|title=''Tithonia rotundifolia''|work=Plant Finder|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b763|location=[[St. Louis|St. Louis, Missouri]]|publisher=[[Missouri Botanical Garden]]|access-date=November 28, 2025|archive-url=https://web.archive.org/web/20250614165428/https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b763|archive-date=June 14, 2025|url-status=live|quote=The blooms are attractive to hummingbirds, butterflies, and other pollinators.}}</ref>
* ''[[Trifolium pratense]]'' – red clover
* ''[[Vernonia altissima]]'' – tall ironweed<ref name="isc"/>
{{div col end}}

Publications have reported that Mexican sunflower (''Tithonia rotundifolia'') is especially attractive to adult monarchs.<ref name=sunflower/> Monarchs obtain moisture and minerals from damp soil and wet gravel, a behavior known as [[mud-puddling]]. The monarch has also been noticed puddling at an oil stain on the pavement.<ref name=isc/>

== Flight and migration ==
[[File:Monarch butterflies (Danaus plexippus plexippus) on Oyamel fir (Abies religiosa) Piedra Herrada.jpg|thumb|upright=0.9|right|Overwintering on Oyamel fir (''[[Abies religiosa]]'')<br />Piedra Herrada, Mexico]]
{{Further|Monarch butterfly migration}}
[[File:Migrating monarch butterflies on pine tree.jpg|thumb|right|upright=0.9|Migrating monarchs resting on a pine tree in [[Fire Island National Seashore]] on [[Fire Island|Fire Island, New York]] (September 2021)]]
In North America, monarchs [[Monarch butterfly migration|migrate]] both north and south on an annual basis, making [[Monarch butterfly migration|long-distance journeys]] that are fraught with risks.<ref name="Agrawal-2017" /> This is a multi-generational migration, with individual monarchs only making part of the full journey.<ref>{{Cite journal|last=Reppert|first=Steven M|title=Demystifying monarch butterfly migration|journal=[[Current Biology]]|year=2018|volume=28 |issue=17|pages=R1009–R1022|doi=10.1016/j.cub.2018.02.067|pmid=30205052|s2cid=52186799|doi-access=free|bibcode=2018CBio...28R1009R }}</ref> The population east of the [[Rocky Mountains]] attempts to migrate to the [[sanctuary|sanctuaries]] of the [[Mariposa Monarca Biosphere Reserve]] in the Mexican state of [[Michoacán]] and parts of Florida. The western population tries to reach [[wikt:overwinter|overwintering]] destinations in various coastal sites in central and southern [[California]]. The populations east of the [[Rocky Mountains]], which mostly [[Monarch butterfly migration|overwinter in central Mexico]], may return the following spring as far north as [[Texas]] and [[Oklahoma]] before producing offspring to carry the journey northward. The second, third, and fourth generations return to their northern locations in the United States and Canada later in the spring and far into the summer.<ref>{{cite web|title=North American Monarch Conservation Plan|url=http://www.mlmp.org/Resources/pdf/5431_Monarch_en.pdf|publisher=Commission for Environmental Cooperation|access-date=October 17, 2014|archive-date=January 28, 2016|archive-url=https://web.archive.org/web/20160128050029/http://mlmp.org/Resources/pdf/5431_Monarch_en.pdf}}</ref>

Flight speeds of adults are around {{cvt|9|km/h|mi/h|0}}. Monarchs travel between 1,200 and 2,800 miles or more from the northeast United States, and southeast Canada, to the mountain forests in central Mexico, where they find the right climate conditions to hibernate from the beginning of November to mid-March.<ref>{{cite web|url=https://www.worldwildlife.org/species/monarch-butterfly|title=MonarchButterfly| publisher=Worldwildlife| date= 2015–2024 |access-date=March 23, 2025}}</ref><ref>{{cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2016/12/31/How-fast-does-a-monarch-fly-A-close-look-at-the-science |title=monarchscience |publisher=Akdavis6.wixsite.com |date=December 31, 2016 |access-date=January 6, 2017}}</ref>

In 2025, Project Monarch deployed over 400 solar-powered ultralight transmitters on the thoraxes of that year's southward-migrating monarchs. A mid-November 2025 web page showed the routes that the monarchs had taken up to that time.<ref>Multiple sources:
* {{cite news|last=Fagin|first=Dan|date=November 17, 2025|title=We Can Now Track Individual Monarch Butterflies. It's a Revelation.|url=https://www.nytimes.com/2025/11/17/science/monarch-butterfly-migration-tracking-sensor.html|newspaper=[[The New York Times]]|location=[[New York City]]|access-date=November 19, 2025}}
* {{cite web|title=Revolutionary tracking study follows monarch butterflies to Mexico using groundbreaking technology and continent-wide collaboration|date=November 17, 2025|url=https://monarchjointventure.org/blog/revolutionary-tracking-study-follows-monarchs|publisher=The Monarch Joint Venture|access-date=November 19, 2025|archive-url=https://web.archive.org/web/20251119175805/https://monarchjointventure.org/blog/revolutionary-tracking-study-follows-monarchs|archive-date=November 19, 2025|url-status=live}}e
* {{cite web|date=September 27, 2025|last=Fisher|first=Ashley|title=With Upgraded Transmitters, We Can Now Track Migrating Monarchs Better Than Ever|url=https://xerces.org/news/organizational-news/with-upgraded-transmitters-we-can-now-track-migrating-monarchs-better-than|location=Portland, Oregon|publisher=[[Xerces Society|The Xerces Society for Invertebrate Conservation]]|access-date=December 3, 2025|archive-url=https://web.archive.org/web/20251204030834/https://xerces.org/news/organizational-news/with-upgraded-transmitters-we-can-now-track-migrating-monarchs-better-than|archive-date=December 4, 2025|url-status=live|quote=A new radiotelemetry transmitter, called the Blu+, is revolutionizing how scientists can track migrating monarchs this fall. The Blu+ transmitter, .... , weighs just 0.06g and can be attached to monarch butterflies.}}</ref>

Captive-raised monarchs appear capable of migrating to overwintering sites in Mexico,<ref>{{cite web|last=Taylor|first=O. R.|title=Monarch Watch 1999 Season Recoveries|pages=1–11|date=August 3, 2000|url=https://www.monarchwatch.org/download/pdf/99rec.pdf|access-date=July 5, 2021|archive-url=https://web.archive.org/web/20140106164758/https://www.monarchwatch.org/download/pdf/99rec.pdf|archive-date=January 6, 2014|url-status=live}}</ref> though they have a much lower migratory success rate than do wild monarchs (see section on captive-rearing below).<ref name=steffy>{{cite journal|doi=10.1093/aesa/sav046 |title=Trends observed in fall migrant Monarch butterflies (Lepidoptera: Nymphalidae) east of the Appalachian Mountains at an inland stopover in southern Pennsylvania over an eighteen year period |journal=[[Annals of the Entomological Society of America]] |volume=108 |issue=5 |page=718 |year=2015 |last1=Steffy |first1=Gayle |s2cid=86201332}}</ref> Monarch overwintering sites have been discovered recently in Arizona.<ref>
{{cite news| title = Monarch butterflies are a steady presence in Arizona |newspaper=Arizona Daily Star |url=http://tucson.com/news/local/monarch-butterflies-are-a-steady-presence-in-arizona/article_efe1d0f4-78de-51a7-a173-00b3545be057.html | access-date=January 15, 2016}}</ref> Monarchs from the eastern US generally migrate longer distances than monarchs from the western US.<ref>{{Cite web|title=Butterfly genomics: Monarchs migrate and fly differently, but meet up and mate|url=https://phys.org/news/2020-07-butterfly-genomics-monarchs-migrate-differently.html|access-date=July 31, 2020 |website=phys.org}}</ref>

Since the 1800s, monarchs have spread globally, and there are now many non-migratory populations.<ref>{{Cite journal|last=Nail|first=Kelly R.|title=Butterflies Across the Globe: A Synthesis of the Current Status and Characteristics of Monarch (''Danaus plexippus'') Populations Worldwide|journal=[[Frontiers in Ecology and Evolution]]|year=2019|volume=27|article-number=362|doi=10.3389/fevo.2019.00362|bibcode=2019FrEEv...7..362N |doi-access=free}}</ref>

Climate change and habitat loss have significantly altered the monarch butterfly’s migration behavior. Rising temperatures and the widespread loss of milkweed (''[[Asclepias]]'' spp.), the primary host plant for monarch larvae, have disrupted breeding and migratory patterns across North America, contributing to population declines over the past two decades.<ref>Grant, T. J., Fisher, K. E., Krishnan, N., Mullins, A. N., Hellmich II, R. L., Sappington, T. W., Adelman, J. S., Coats, J. R., Hartzler, R. G., Pleasants, J. M., & Bradbury, S. P. (2022). Monarch butterfly ecology, behavior, and vulnerabilities in North Central United States agricultural landscapes. BioScience, 72(12), 1176–1203. https://doi.org/10.1093/biosci/biac094
</ref><ref>Flockhart, D. T. T., Pichancourt, J. B., Norris, D. R., & Martin, T. G. (2015). Unravelling the annual cycle in a migratory animal: Breeding-season habitat loss drives population declines of monarch butterflies. Journal of Animal Ecology, 84(1), 155–165. https://doi.org/10.1111/1365-2656.12253
</ref>

== Interactions with predators ==
In both caterpillar and butterfly forms, monarchs are [[aposematism|aposematic]], warding off predators with a bright display of contrasting colors to warn potential predators of their undesirable taste and poisonous characteristics. One monarch researcher emphasizes that predation on eggs, larvae, or adults is natural since monarchs are part of the food chain, thus people should not take steps to kill predators of monarchs.<ref>{{cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2016/04/05/Very-interesting-study-on-monarch-predators-recently-published |title=monarchscience |publisher=Akdavis6.wixsite.com |date=April 5, 2016}}</ref>

Larvae feed exclusively on [[Asclepias|milkweed]] and consume protective cardiac glycosides. Toxin levels in the ''Asclepias'' species vary. Not all monarchs are unpalatable, but exhibit [[Batesian mimicry|Batesian]] or [[Automimicry|automimics]]. Cardiac glycoside levels are higher in the abdomen and wings. Some predators can differentiate between these parts and consume the most palatable ones.<ref name="Barbosa">{{cite book |last=Barbosa |first=Pedro |author2=Deborah Kay Letourneau |title=Novel Aspects of Insect-plant Interactions |chapter-url=https://books.google.com/books?id=2fZbhllItE4C&pg=PA45 |year=1988 |publisher=Wiley-Interscience |isbn=978-0-471-83276-8 |pages=[https://archive.org/details/novelaspectsofin1988unse/page/29 29–31] |chapter=5 |url=https://archive.org/details/novelaspectsofin1988unse/page/29}}</ref>

Butterfly weed (''A. tuberosa'') lacks significant amounts of cardiac glycosides (cardenolides) but instead contains other types of toxic glycosides, including [[pregnane]]s.<ref>Multiple sources:
* {{cite web|url=https://www.co.becker.mn.us/dept/soil_water/PDFs/flowers_grasses/Butterfly%20Weed.pdf|title=Butterfly Weed: ''Asclepias tuberosa''|location=[[Becker County, Minnesota]]|publisher=Becker Soil and Water Conservation District|access-date=September 11, 2020|quote=Unlike other milkweeds, this plant has a clear sap, and the level of toxic cardiac glycosides is consistently low (although other toxic compounds may be present).|archive-url=https://web.archive.org/web/20200911011945/https://www.co.becker.mn.us/dept/soil_water/PDFs/flowers_grasses/Butterfly%20Weed.pdf|archive-date=September 11, 2020|url-status=live}}
* {{cite journal|first1=Lauge Hjorth|last1=Mikkelsen|first2=Hassan|last2=Hamoudi|first3=Cigdem|last3=Altuntas Gül|first4=Steffen|last4=Heegaard|title=Corneal Toxicity Following Exposure to ''Asclepias tuberosa''|journal=[[The Open Ophthalmology Journal]] |year=2017 |volume=11 |pages=1–4 |pmid=28400886 |pmc=5362972 |doi= 10.2174/1874364101711010001 |doi-access=free|publisher=[[Bentham Science Publishers]]|quote=The latex of ''A. tuberosa'' seems to be different from other ''Asclepias'' species since even though cardenolides are normally present in ''Asclepias'' species, these cardenolides have not been found in ''A. tuberosa''. Instead some unique [[pregnane]] glycosides are found in ''A. tuberosa''.}}
* {{cite journal|first1=Tsutomu|last1=Warashina|first2=Tadataka|last2=Noro|url=https://www.jstage.jst.go.jp/article/cpb/58/2/58_2_172/_pdf/-char/en|title=8,12;8,20-Diepoxy-8,14-secopregnane Glycosides from the Aerial Parts of ''Asclepias tuberosa''|journal=[[Chemical and Pharmaceutical Bulletin]] |date=February 2010|volume=58|issue=2|pages=172–179|pmid=20118575|doi=10.1248/cpb.58.172|publisher=Pharmaceutical Society of Japan|access-date=September 11, 2020|quote=Though cardenolides are considered to be characteristic constituents of ''Asclepias'' spp. together with pregnane glycosides, we could find no cardenolides in the more hydrophobic fraction of the methanol extract of the aerial parts of ''A. tuberosa'', the same as previously.|doi-access=free}}</ref> This difference may reduce the toxicity of monarchs whose larvae feed on that milkweed species and affect the butterfly's breeding choices, as a naturalist and others have reported that egg-laying monarchs do not favor the plant.<ref name=Abugattas>Multiple sources:
* {{cite web|first=John|last=Gunn|url=http://midatlanticgardener.com/alonso-abugattas-native-plant-wildlife/|title=Milkweeds (mostly ''Asclepias'' spp.)|work=Alonso Abugattas Shares Native Plant Picks for Wildlife|date=May 20, 2016|publisher=Mid-Atlantic Gardener (John Gunn)|access-date=October 17, 2020|quote=And if you have hot, dry conditions in your yard, try Butterflyweed (''A. tuberosa'').{{nbsp}}... It's the least favored by Monarch caterpillars because it has very little toxin (cardiac glycosides) in its leaves.|archive-url=https://web.archive.org/web/20201021024837/https://midatlanticgardener.com/alonso-abugattas-native-plant-wildlife/|archive-date=October 21, 2020}}
* {{cite web|last=Abugattas|first=Alonzo|url=http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|access-date=June 5, 2017|title=Monarch Way Stations|work=Capital Naturalist|date=January 3, 2017|via=[[Blogger (service)|Blogger]]|quote=(''A. tuberosa'') is the least favored by monarch caterpillars{{nbsp}}... because it has very little toxin (cardiac glycosides) in its leaves|archive-url=https://web.archive.org/web/20170605221624/http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|archive-date=June 5, 2017|url-status=live}}
* {{cite web|last=Gomez|first=Tony|url=https://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-tuberosa-butterfly-weed/|title=''Asclepias tuberosa'': Butterfly Weed for Monarchs and More|work=Monarch Butterfly Garden|publisher=MonarchButterflyGarden.net|access-date=October 17, 2010|quote=Rough leaves for monarch caterpillars, not typically a heavily used host plant|archive-url=https://web.archive.org/web/20170816204046/https://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-tuberosa-butterfly-weed/|archive-date=August 16, 2017|url-status=live}}
* {{cite web|author=Butterfly Society of Virginia|year=2019|title=Growing Milkweed|url=https://www.butterflysocietyofva.org/Growing-Milkweed|access-date=December 25, 2023|archive-url=https://web.archive.org/web/20190624061425/https://www.butterflysocietyofva.org/Growing-Milkweed|archive-date=June 24, 2019|quote=I've grown butterfly weed, swamp milkweed, Asclepias currassavica (bloodflower), Asclepias syriaca (common milkweed), and Asclepias verticillata (whorled milkweed). I've found that butterfly weed is the least favorite of my Monarch guests in my Virginia Beach garden for laying eggs (perhaps the leaves are tougher?)|url-status=live}}
* {{cite journal|first1=Victoria M.|last1= Pocius|first2=Diane M.|last2=Debinski|first3=John M.|last3=Pleasants|first4=Keith G.|last4=Bidne|first5=Richard L.|last5=Hellmich|date=January 8, 2018|title=Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species|doi=10.1002/ecs2.2064|journal=[[Ecosphere (journal)|Ecosphere]] |volume=9|issue=1|pages=1–13|article-number= e02064|publisher=[[Ecological Society of America]]|quote=In our study, the least preferred milkweed species ''A. tuberosa'' (no choice; Fig. 2) and ''A. verticillata'' (choice; Fig. 3A) both have low cardenolide levels recorded in the literature (Roeske et al. 1976, Agrawal et al. 2009, 2015, Rasmann and Agrawal 2011) |doi-access=free|bibcode= 2018Ecosp...9E2064P}}</ref> Some other milkweeds have similar characteristics.<ref>{{cite journal|first1=Victoria M.|last1= Pocius|first2=Diane M.|last2=Debinski|first3=John M.|last3=Pleasants|first4=Keith G.|last4=Bidne|first5=Richard L.|last5=Hellmich|date=January 8, 2018|title=Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species|doi=10.1002/ecs2.2064|journal=[[Ecosphere (journal)|Ecosphere]] |volume=9|issue=1|pages=1–13|article-number= e02064|publisher=[[Ecological Society of America]]|quote=In our study, the least preferred milkweed species ''A. tuberosa'' (no choice; Fig. 2) and ''A. verticillata'' (choice; Fig. 3A) both have low cardenolide levels recorded in the literature (Roeske et al. 1976, Agrawal et al. 2009, 2015, Rasmann and Agrawal 2011) |doi-access=free|bibcode= 2018Ecosp...9E2064P}}</ref>

=== Types of predators ===
[[File:Wasp takes caterpillar.webm|thumb|thumbtime=90|A [[European paper wasp]] takes a [[monarch|monarch butterfly]] [[caterpillar]] from within a [[Asclepias fascicularis|narrow leaf milkweed]] [[umbel]]. Part is shown at one fourth speed.]]

While monarchs have a wide range of natural predators, none of these is suspected of causing harm to the overall population, or are the cause of the long-term declines in winter colony sizes.

Several species of birds have acquired methods that allow them to ingest monarchs without experiencing the ill effects associated with the cardiac glycosides (cardenolides). The [[black-backed oriole]] can eat the monarch through an [[exaptation]] of its feeding behavior that gives it the ability to identify cardenolides by taste and reject them.<ref name="Brower1988">{{cite journal|last=Brower|first=Lincoln|title=Avian Predation on the Monarch Butterfly and Its Implications for Mimicry Theory|journal=[[The American Naturalist]]|year=1988|volume=131|pages=S4–S6|doi=10.1086/284763|bibcode=1988ANat..131S...4B |s2cid=84642806}}</ref> The [[black-headed grosbeak]], though, has developed an insensitivity to secondary plant poisons that allows it to ingest monarchs without vomiting.<ref>{{Cite journal|last1=Fink|first1=Linda S.|last2=Brower|first2=Lincoln P.|date=May 1981|title=Birds can overcome the cardenolide defence of monarch butterflies in Mexico|journal=Nature|volume=291|issue=5810|pages=67–70|doi=10.1038/291067a0|bibcode=1981Natur.291...67F|s2cid=4305401|issn=0028-0836}}</ref> As a result, these orioles and grosbeaks periodically have high levels of cardenolides in their bodies, and they are forced to go on periods of reduced monarch consumption. This cycle effectively reduces potential predation of monarchs by 50% indicating that monarch aposematism has a legitimate purpose.<ref name="Brower1988" /> The black-headed grosbeak has also evolved resistance mutations in the molecular target of the heart poisons, the sodium pump. The specific mutations that evolved in one of the grosbeak's four copies of the sodium pump gene are the same as those found in some rodents that have also evolved to resist cardiac glycosides.<ref>{{Cite journal|last1=Groen|first1=Simon C.|last2=Whiteman|first2=Noah K.|date=November 2021|title=Convergent evolution of cardiac-glycoside resistance in predators and parasites of milkweed herbivores|journal=Current Biology|volume=31|issue=22|pages=R1465–R1466|doi=10.1016/j.cub.2021.10.025|pmid=34813747|pmc=8892682 |bibcode=2021CBio...31R1465G |s2cid=244485686|issn=0960-9822}}</ref> Known bird predators include [[brown thrasher]]s, [[grackle]]s, [[American robin|robins]], [[northern cardinal|cardinals]], [[Old World sparrow|sparrow]]s, [[scrub jay]]s, and [[pinyon jay]]s.<ref name="Barbosa" />
[[File:Chinese Mantis, Sand Ridge State Forest, Mason County, IL imported from iNaturalist photo 2924074.jpg|thumb|[[Chinese mantis]] feeding on a monarch butterfly. The species also feeds on monarch caterpillars, being resistant to their toxins and gutting them before consumption to remove most of the toxins.<ref>{{Cite journal |last1=Mebs |first1=Dietrich |last2=Wunder |first2=Cora |last3=Pogoda |first3=Werner |last4=Toennes |first4=Stefan W. |date=2017-06-01 |title=Feeding on toxic prey. The praying mantis (Mantodea) as predator of poisonous butterfly and moth (Lepidoptera) caterpillars |url=https://linkinghub.elsevier.com/retrieve/pii/S0041010117300971 |journal=Toxicon |volume=131 |pages=16–19 |doi=10.1016/j.toxicon.2017.03.010 |pmid=28300580 |bibcode=2017Txcn..131...16M |issn=0041-0101|url-access=subscription }}</ref>]]
The monarch's white [[Polymorphism (biology)|morph]] appeared in Oahu after the 1965–1966 introduction of two [[bulbul]] bird species, ''[[Pycnonotus cafer]]'' and ''[[Pycnonotus jocosus]]''. These are now the most common avian [[insectivore]]s in Hawaii, and probably the only ones that eat insects as large as monarchs. Although Hawaiian monarchs have low cardiac glycoside levels, the birds may also be [[Physiological tolerance|tolerant]] of that toxin. The two species hunt the larvae and some pupae from the branches and undersides of leaves in milkweed bushes. The bulbuls also eat resting and ovipositing adults, but rarely flying ones. Because of its color, the white morph has a higher survival rate than the orange one. This is either because of [[apostatic selection]] (i.e., the birds have learned the orange monarchs can be eaten), because of [[camouflage]] (the white morph matches the white pubescence of milkweed or the patches of light shining through foliage), or because the white morph does not fit the bird's search image of a typical monarch, so is thus avoided.<ref>{{cite journal |last=Stimson |first=John |author2=Mark Berman |year=1990 |title= Predator induced colour polymorphism in ''Danaus plexippus'' L. (Lepidoptera: Nymphalidae) in Hawaii |journal=[[Heredity (journal)|Heredity]]|volume=65 |issue=3 |pages=401–406 |doi= 10.1038/hdy.1990.110 |doi-access=free|bibcode=1990Hered..65..401S }}</ref>

[[File:Monarch Predators.webm|thumb|right|upright=0.9| thumbtime=0|1) A stink (shield) bug killing and consuming a fourth-instar monarch larva. 2) A mature fifth instar larva jerking to dislodge a large milkweed bug (a herbivore). 3) A fourth-instar larva killed by insect parasitoids, non-insect parasites, or a pathogen.]]
Some mice, particularly the black-eared mouse (''[[Peromyscus melanotis]]''), are, like all rodents, able to tolerate large doses of cardenolides and can eat monarchs.<ref name="mammalspecies">{{cite journal|last1=Álvarez-Castañeda|first1=Sergio Ticul|date=2005|title=''Peromyscus melanotis''|journal=[[Mammalian Species]] |volume=2005|issue=764|pages=1–4|doi=10.1644/1545-1410(2005)764[0001:PM]2.0.CO;2|s2cid=198968529}}</ref> Overwintering adults become less toxic over time making them more vulnerable to predators. In Mexico, about 14% of the overwintering monarchs are eaten by birds and mice and black-eared mice can eat up to 40 monarchs per night.<ref name="rcgt" /><ref name="mammalspecies"/>

In North America, eggs and first-instar larvae of the monarch are eaten by larvae and adults of the [[Introduced species|introduced]] Asian lady beetle (''[[Harmonia axyridis]]'').<ref>{{cite journal |last=Koch |first=R. L. |author2=W. D. Hutchison |author3=R. C. Venette |author4=G. E. Heimpel |date=October 2003 |title=Susceptibility of immature monarch butterfly, ''Danaus plexippus'' (Lepidoptera: Nymphalidae: Danainae), to predation by ''Harmonia axyridis'' (Coleoptera: Coccinellidae) |journal=Biological Control |volume=28 |issue=2 |pages=265–270 |doi=10.1016/S1049-9644(03)00102-6|bibcode=2003BiolC..28..265K }}</ref> The Chinese mantis (''[[Tenodera sinensis]]'') will consume the larvae once the gut is removed thus avoiding cardenolides.<ref>{{cite journal|last=Rafter|first=Jamie|author2=Anurag Agruwal |author3=Evan Preisser |title=Chinese mantids gut caterpillars: avoidance of prey defense?|doi=10.1111/j.1365-2311.2012.01408.x|journal=[[Ecological Entomology]] |volume=38|year=2013|issue=1|pages=78–82|s2cid=15029022 |url=https://digitalcommons.uri.edu/bio_facpubs/627 }}</ref> Predatory wasps commonly consume larvae.<ref>{{cite journal|title=It's the first bites that count: Survival of first-instar monarchs on milkweeds|journal=[[Austral Ecology]]|year=2001|volume=26|issue=5|pages=547–555|doi=10.1046/j.1442-9993.2001.01132.x |last1=Zalucki|first1=Myron P.|last2=Malcolm|first2=Stephen B.|last3=Paine|first3=Timothy D.|last4=Hanlon|first4=Christopher C.|last5=Brower|first5=Lincoln P.|last6=Clarke|first6=Anthony R.|bibcode=2001AusEc..26..547Z }}</ref> Many Hemipteran bugs including [[Predation|predatory]] [[stink bug]]s in the subfamily [[Asopinae]] and assassin bugs in family [[Reduviidae]] eat monarchs. Larvae can sometimes avoid predation by dropping from the plant or by jerking their bodies.{{sfn|Oberhauser|2004|p=44}}

[[Parasitoid]]s, including [[Tachinidae|tachinid flies]] and [[Braconidae|braconid wasps]] develop inside the monarch larvae eventually killing them and emerging from the larvae or pupa. Non-insect parasites and infectious diseases ([[pathogen]]s) also kill monarchs.

=== Aposematism ===
[[File:Oleandrin-skeletal.svg|thumb|Chemical structure of [[oleandrin]], one of the [[cardiac glycoside]]s]]
Monarchs are toxic and foul-tasting because of the presence of cardenolides in their bodies, which the caterpillars ingest as they feed on milkweed.<ref name="animaldiversity1" /> Monarchs and other cardenolide-resistant insects rely on a resistant form of the [[Na+/K+-ATPase|Na+/ K+-ATPase]] enzyme to tolerate significantly higher concentrations of cardenolides than nonresistant species.<ref name="Karageorgi-2019">{{Cite journal|last1=Karageorgi|first1=Marianthi|last2=Groen|first2=Simon C.|last3=Sumbul|first3=Fidan|last4=Pelaez|first4=Julianne N.|last5=Verster|first5=Kirsten I.|last6=Aguilar|first6=Jessica M.|last7=Hastings|first7=Amy P.|last8=Bernstein|first8=Susan L.|last9=Matsunaga|first9=Teruyuki|last10=Astourian|first10=Michael|last11=Guerra|first11=Geno|date=October 2019|title=Genome editing retraces the evolution of toxin resistance in the monarch butterfly|journal=Nature|volume=574|issue=7778|pages=409–412|doi=10.1038/s41586-019-1610-8|pmid=31578524|pmc=7039281|bibcode=2019Natur.574..409K |issn=1476-4687}}</ref> By ingesting a large number of plants in the genus ''[[Asclepias]]'', primarily milkweed, monarch caterpillars can sequester cardiac glycosides, or more specifically [[cardenolide]]s, which are steroids that act in heart-arresting ways similar to [[digitalis]].<ref name=parsons_digitalis>{{cite journal|last=Parsons|first=J.A.|pmid=14298120 |pmc=1357291| title=A Digitallis-like Toxin in the Monarch Butterfly ''Danaus plexippus'' L|journal=[[The Journal of Physiology]] |volume=178|year=1965 |issue=2|pages=290–304|doi=10.1113/jphysiol.1965.sp007628 |bibcode=1965JPhsg.178..290P }}</ref> It has been found that monarchs can sequester cardenolides most effectively from plants of intermediate cardenolide content rather than those of high or low content.<ref name=malcolm_evolutionary>{{cite journal | last=Malcolm | first=S. B. | author2=L. P. Brower | title=Evolutionary and ecological implications of cardenolide sequestration in the monarch butterfly | journal=[[Experientia]] | year=1989 | volume=45 | issue=3 | pages=284–295 | doi=10.1007/BF01951814| s2cid=9967183}}</ref> Three mutations that evolved in the monarch's [[Na+/K+-ATPase|Na+/ K+-ATPase]] were found to be sufficient together to confer resistance to dietary cardiac glycosides.<ref name="Karageorgi-2019" /> This was tested by swapping these mutations into the same gene in the fruit fly ''[[Drosophila melanogaster]]'' using [[CRISPR gene editing|CRISPR-Cas9]] genome editing. These fruit flies-turned monarch flies<ref>{{Cite web|title=CRISPRed flies mimic monarch butterfly — and could make you vomit {{!}} Research UC Berkeley|url=https://vcresearch.berkeley.edu/news/crispred-flies-mimic-monarch-butterfly-and-could-make-you-vomit|access-date=2021-12-18|website=vcresearch.berkeley.edu}}</ref> were completely resistant to dietary [[ouabain]], a cardiac glycoside found in [[Apocynaceae]], and even sequestered some through metamorphosis, like the monarch.<ref name="Karageorgi-2019" />

Different milkweed species have variable effects on parasite growth, virulence, and transmission.<ref name=deRood_Virulence>{{cite journal | last1=de Rood | first1=J. C. | title=Virulence evolution in response to anti-infection resistance: toxic food plants can select for virulent parasites of monarch butterflies |pmid=21261772| journal=[[Journal of Evolutionary Biology]] | year=2011 | volume=24 | issue=4 | pages=712–722| last2=De Castillejo | first2=C. L. | last3=Faits | first3=T. | last4=Alizon | first4=S. | doi=10.1111/j.1420-9101.2010.02213.x| s2cid=1533504 | doi-access=}}</ref> One species, ''[[Asclepias curassavica]]'', appears to reduce the symptoms of ''[[Ophryocystis elektroscirrha]]'' (OE) infection. The two possible explanations for this include that it promotes overall monarch health to boost the monarch's immune system or that chemicals from the plant have a direct negative effect on the OE parasites.<ref name="deRood_Virulence" /> ''A. curassavica'' does not cure or prevent the infection with OE; it merely allows infected monarchs to live longer, and this would allow infected monarchs to spread the OE spores for longer periods. For the average home butterfly garden, this scenario only adds more OE to the local population.<ref>{{Cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2017/03/15/Is-tropical-milkweed-really-medicinal-answer-yes-and-thats-really-really-bad-for-your-garden|title=Is tropical milkweed really medicinal? (answer: yes, and that's really really bad for your garden)|website=monarchscience |date=March 16, 2017|access-date=December 12, 2019}}</ref>

After the caterpillar becomes a butterfly, the toxins shift to different body parts. Since many birds attack the butterfly's wings, having three times the cardiac glycosides in the wings leaves predators with a foul taste and may prevent them from ever ingesting the butterfly's body.<ref name="parsons_digitalis" /> To combat predators that remove the wings only to ingest the abdomen, monarchs keep the most potent cardiac glycosides in their abdomens.<ref>{{cite journal|last=Glazier|first=Lincoln|author2=Susan Glazier|title=Localization of Heart Poisons in the Monarch Butterfly |journal=[[Science (journal)|Science]] |year=1975 |volume=188 |pages=19–25| bibcode=1975Sci...188...19B|doi=10.1126/science.188.4183.19|pmid=17760150|issue=4183|s2cid=44509809}}</ref>

=== Mimicry ===
[[File:Monarch Viceroy Mimicry Comparison.jpg|right|thumb|Monarch (left) and viceroy (right) butterflies exhibiting [[Müllerian mimicry]]]]

Monarchs share the defense of noxious taste with the similar-appearing [[viceroy butterfly]] in what is perhaps one of the most well-known examples of [[mimicry]]. Though long purported to be an example of [[Bates mimicry|Batesian mimicry]], the viceroy is more unpalatable than the monarch, making this a case of [[Müllerian mimicry]].<ref name=Ritland>{{cite journal |last=Ritland |first=D.|author2=L. P. Brower|year=1991 |title=The viceroy butterfly is not a Batesian mimic |journal=Nature |volume=350 |issue= 6318|pages=497–498 |doi =10.1038/350497a0 |quote=Viceroys are as unpalatable as monarchs, and significantly more unpalatable than queens from representative Florida populations.|bibcode=1991Natur.350..497R|s2cid=28667520}}</ref>

== Human interaction ==
The monarch is the [[List of U.S. state insects|state insect]] of [[Alabama]],<ref>{{cite web |url=http://www.archives.state.al.us/emblems/st_insec.html |title=Official Alabama Insect |access-date=March 19, 2007 |date=July 12, 2001 |work=Alabama Emblems, Symbols and Honors |publisher=Alabama Department of Archives & History |archive-date=October 14, 2018 |archive-url=https://web.archive.org/web/20181014061225/http://www.archives.state.al.us/emblems/st_insec.html }}</ref> [[Idaho]],<ref>{{cite web |url=http://www.shgresources.com/id/symbols/insect/ |title=Idaho Symbols, Insect: Monarch Butterfly |access-date=March 26, 2008 |work=Idaho State Symbols, Emblems, and Mascots |publisher=SHG resources, state handbook & guide |archive-date=February 8, 2012 |archive-url=https://web.archive.org/web/20120208022908/http://www.shgresources.com/id/symbols/insect/ }}</ref> [[Illinois]],<ref>{{cite web |url=http://www.museum.state.il.us/exhibits/symbols/insect.html |title=State Symbol: Illinois Official Insect — Monarch Butterfly (''Danaus plexippus'') |access-date=March 26, 2008 |work=[Illinois] State Symbols |publisher=Illinois State Museum}}</ref> [[Minnesota]],<ref>{{cite web |url= http://www.house.leg.state.mn.us/hinfo/govser/GOVSER2.pdf |access-date=March 26, 2008 |title=Minnesota State Symbols |publisher= Minnesota House of Representatives}}</ref> [[Texas]],<ref>{{cite web |url=http://www.tsl.state.tx.us/ref/abouttx/symbols.html |access-date=March 26, 2008 |title=Texas State Symbols |publisher=The Texas State Library and Archives |archive-date=December 24, 2018 |archive-url=https://web.archive.org/web/20181224225022/https://www.tsl.texas.gov/ref/abouttx/symbols.html }}</ref> [[Vermont]],<ref>{{cite web |url=http://www.libraries.vermont.gov/www/html/emblems/butterfly.htm |access-date=March 26, 2008 |title=(Vermont) State Butterfly |publisher=Vermont Department of Libraries |archive-url = https://web.archive.org/web/20080518004053/http://www.libraries.vermont.gov/www/html/emblems/butterfly.htm <!-- Bot retrieved archive --> |archive-date=May 18, 2008}}</ref> and [[West Virginia]].<ref>{{cite web |url=http://www.wv.gov/govdirectory/statgeninfo.pdf |access-date=March 26, 2008 |title=West Virginia Statistical Information, General State Information |publisher=Official West Virginia Web Portal |archive-url = https://web.archive.org/web/20080411045927/http://www.wv.gov/govdirectory/statgeninfo.pdf <!-- Bot retrieved archive --> |archive-date=April 11, 2008}}</ref> Legislation was introduced to make it the national insect of the United States,<ref>{{cite news |first=Nicholas |last=Wade |title=Choosing a National Bug |work=The New York Times |date=June 1, 1990 |access-date=September 27, 2017 |url=https://www.nytimes.com/1990/06/01/opinion/the-editorial-notebook-choosing-a-national-bug.html}}</ref> but this failed in 1989<ref>{{cite web|url=https://www.govtrack.us/congress/bills/101/hjres411|title=Designating the monarch butterfly as the national insect. (1989 - H.J.Res. 411)|website=GovTrack.us}}</ref> and again in 1991.<ref>{{cite web|url=https://www.govtrack.us/congress/bills/102/hjres200|title=Designating the monarch butterfly as the national insect. (1991 - H.J.Res. 200)|website=GovTrack.us}}</ref>

Homeowners are increasingly establishing butterfly gardens; monarchs can be attracted by cultivating a [[Butterfly gardening|butterfly garden]] with specific milkweed species and nectar plants. Efforts are underway to establish these monarch waystations.
<ref>{{cite web|archive-url=https://web.archive.org/web/20191118213225/https://www.monarchwatch.org/waystations/index.html|archive-date=November 18, 2019 |url=https://www.monarchwatch.org/waystations/index.html|url-status=live|title=Monarch Watch: Monarch Waystation Program|access-date=February 26, 2019 |work=[[University of Kansas]], Entomology Department}}
</ref>

A 2012 [[IMAX]] film, ''[[Flight of the Butterflies]]'', describes the story of the [[Fred Urquhart|Urquharts]], [[Kenneth C. Brugger|Brugger]], and [[Catalina Trail|Trail]] to document the then-unknown monarch migration to Mexican overwintering areas.<ref name="Fleet">{{cite web|url=http://www.rhfleet.org/shows/flight-butterflies|title=Flight of the Butterflies|work=Reuben H. Fleet Science Center|access-date=February 18, 2013|archive-url=https://web.archive.org/web/20130217100436/http://rhfleet.org/shows/flight-butterflies|archive-date=February 17, 2013}}</ref>

Sanctuaries and reserves have been created at overwintering locations in Mexico and California to limit [[habitat destruction]]. These sites can generate significant tourism revenue.<ref>{{cite web |url= https://www.sciencedaily.com/videos/2005/0810-saving_butterflies.htm |title= Saving Butterflies: Insect Ecologist Spearheads Creation of Oases for Endangered Butterflies |access-date=May 27, 2008 |work= ScienceDaily |date=January 1, 2005 |archive-url= https://web.archive.org/web/20080604045408/https://www.sciencedaily.com/videos/2005/0810-saving_butterflies.htm |archive-date=June 4, 2008}}</ref> However, with less tourism, monarch butterflies may exhibit higher survival rates, as butterflies in tourist isolated areas have shown increases in protein content, immune response and oxidative defense.<ref>{{cite journal|first1=Mélanie|last1=Nicoletti|first2=Florent|last2=Gilles|first3=Ivette|last3=Galicia-Mendoza|first4=Eduardo|last4=Rendón-Salinas|first5=Alfonso|last5=Alonso|first6=Jorge|last6=Contreras-Garduño|title=Physiological Costs in Monarch Butterflies Due to Forest Cover and Visitors|journal=Ecological Indicators|volume=117|year=2020|article-number=106592|doi=10.1016/j.ecolind.2020.106592|doi-access=free|bibcode=2020EcInd.11706592N }}</ref>

Organizations and individuals participate in tagging programs. Tagging information is used to study migration patterns.<ref>{{cite web|url=http://www.birdcapemay.org/monarch.shtml|title=Monarch Monitoring Project|access-date=December 5, 2008|publisher= Cap May Bird Observatory|year= 2008|archive-url=https://web.archive.org/web/20081220150017/http://www.birdcapemay.org/monarch.shtml|archive-date=December 20, 2008}}</ref>

The 2012 novel by [[Barbara Kingsolver]], ''[[Flight Behavior]]'', deals with the fictional appearance of a large population in the [[Appalachians]].<ref>{{cite book |last=Kingsolver |first=Barbara |title=[[Flight Behavior]] |date=2012 |publisher=HarperCollins}}</ref>

=== Captive rearing ===
Humans interact with monarchs when rearing them in captivity, which has become increasingly popular. However, risks occur in this controversial activity. On one hand, captive rearing has many positive aspects. Monarchs are bred in schools and used for butterfly releases at hospices, memorial events, and weddings.<ref>{{cite web|title=Live butterfly release for funerals and butterfly weddings|publisher=Fragrant Acres Butterfly Farm|url=http://www.butterflyreleases.com/|access-date=November 14, 2014}}</ref> Memorial services for the [[September 11 attacks]] include the release of captive-bred monarchs.<ref>Multiple sources:
* {{cite web|title =In Memory of 9/11 "Wings of Hope"|publisher= gayandciha.com|date=September 4, 2014|url=http://gayandciha.com/in-memory-of-911-wings-of-hope-2014/|access-date=November 14, 2014}}
* {{cite news|last1=Johnson|first1=Pam|title=Join Branford Rotary's 9/11 Town Green Event/Butterfly Release|url=http://www.theday.com/article/20110824/NWS01/308259715|access-date=November 14, 2014|agency=The Day|publisher=Shure Publishing|date=August 24, 2010}}
* {{cite news|title=Ormond Beach Flying US Flags On Granada Bridge To Mark 9/11 Anniversary|url=http://newsdaytonabeach.com/ormond-beach-placing-u-s-flags-on-granada-bridge-to-mark-911-anniversary/|year=2013|access-date=November 14, 2014|agency=WNDB Local News First|publisher=NewsDaytonaBeach.com|archive-url=https://web.archive.org/web/20141129031447/http://newsdaytonabeach.com/ormond-beach-placing-u-s-flags-on-granada-bridge-to-mark-911-anniversary/|archive-date=November 29, 2014}}</ref> Monarchs are used in schools and nature centers for educational purposes.<ref>{{cite web|title=Monarch Butterfly release at Children's Museum of Fond du Lac|publisher=FDL Reporter|url=http://www.fdlreporter.com/picture-gallery/news/local/2014/08/16/monarch-butterfly-release-at-childrens-museum-of-fond-du-lac/14177519/|access-date=November 14, 2014}}</ref> Adult monarchs will extend their [[proboscis#Lepidoptera mouth parts|proboscises]] to reach people's fingertips.<ref>{{cite web|first=Konstantin|last=Khrapko|title=Waltz of Proboscises. Monarchs dancing on the fingertips.|date=September 14, 2023 |
url=https://www.youtube.com/watch?v=3brZuY-yWh0|via=[[YouTube]]|access-date=September 26, 2025}} Video: 0:36 minutes</ref> With assistance, they will also extend their proboscises into a dish containing artificial food.<ref>{{cite web|first=Konstantin|last=Khrapko|title=How to feed a monarch|
url=https://www.youtube.com/shorts/5KH3NLDaRvU|via=[[YouTube]]|access-date=September 26, 2025}}</ref>

On the other hand, this practice becomes problematic when monarchs are "mass-reared". Stories in the ''[[Huffington Post]]'' in 2015 and ''[[Discover (magazine)|Discover]]'' magazine in 2016 have summarized the controversy around this issue.<ref>Multiple sources:
* {{cite web|author=John Platt TakePart |url=https://www.huffingtonpost.com/entry/butterfly-releases_us_561de4eae4b028dd7ea5bcc2 |title=When Butterflies Shouldn't Fly Free |work=[[The Huffington Post]] |date=October 14, 2015 |access-date=January 12, 2017}}
* {{cite web|url=http://blogs.discovermagazine.com/crux/2016/06/21/are-we-loving-monarchs-to-death/#.WHJdexsrLIU |title=Are We Loving Monarchs to Death? – The Crux |website=[[Discover (magazine)|Discover]]|date=June 21, 2016|access-date=January 12, 2017|archive-url=https://web.archive.org/web/20200414133927/https://www.discovermagazine.com/planet-earth/are-we-loving-monarchs-to-death|archive-date=April 14, 2020}}</ref>

The frequent media reports of monarch declines have encouraged many homeowners to attempt to rear as many monarchs as possible in their homes and then release them to the wild to "boost the monarch population". Some individuals, such as one in [[Linn County, Iowa]], have reared thousands of monarchs at the same time.<ref>{{cite web|author=Love, Orlan |url=http://www.thegazette.com/subject/news/business/agriculture/monarch-moonshot-officials-hope-to-make-linn-county-center-of-butterfly-production-and-habitat-20160825 |title= Monarch Moonshot: Officials hope to make Linn County center of butterfly production and habitat |publisher=The Gazette |date=August 25, 2016 |access-date=January 12, 2017}}</ref>

Some monarch scientists do not condone the practice of rearing "large" numbers of monarchs in captivity for release into the wild because of the risks of genetic issues and disease spread.<ref>[http://monarchjointventure.org/images/uploads/documents/Monarch_Rearing_Instructions.pdf Rearing Monarchs Responsibly: A conservationist's guide to raising monarchs for science and education] {{Webarchive|url=https://web.archive.org/web/20210914163519/http://monarchjointventure.org/images/uploads/documents/Monarch_Rearing_Instructions.pdf |date=September 14, 2021}}. Monarch Joint Venture, University of Minnesota</ref> One of the biggest concerns of mass rearing is the potential for spreading the monarch parasite ''Ophryocystis elektroscirrha'' into the wild. This parasite can rapidly build up in captive monarchs, especially if they are housed together. The parasite spores can quickly contaminate all housing equipment so all subsequent monarchs reared in the same containers become infected. One researcher stated that rearing more than 100 monarchs constitutes "mass rearing" and should not be done.<ref>{{cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2015/09/07/What-everyone-needs-to-know-about-rearing-monarchs-from-a-science-standpoint |title=monarchscience |publisher=Akdavis6.wixsite.com |date=September 7, 2015}}</ref>

In addition to the disease risks, researchers believe these captive-reared monarchs are not as fit as wild ones, owing to the unnatural conditions in which they are raised. Homeowners often raise monarchs in plastic or glass containers in their kitchens, basements, porches, etc., and under artificial lighting and controlled temperatures. Such conditions would not mimic what the monarchs are used to in the wild and may result in adults unsuited for the realities of their wild existence. In support of this, a recent study by a [[Citizen science|citizen scientist]] found that captive-reared monarchs have a lower migration success rate than wild monarchs.<ref name=steffy/>

A 2019 study shed light on captive-reared monarchs' fitness by testing reared and wild monarchs on a tethered flight apparatus that assessed navigational ability.<ref>{{Cite journal|last1=Tenger-Trolander|first1=Ayşe|last2=Lu|first2=Wei|last3=Noyes|first3=Michelle|last4=Kronforst|first4=Marcus R.|date=July 16, 2019 |title=Contemporary loss of migration in monarch butterflies|journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=116 |issue=29 |pages=14671–14676 |doi=10.1073/pnas.1904690116 |issn=0027-8424 |pmc=6642386 |pmid=31235586|bibcode=2019PNAS..11614671T |doi-access=free}}</ref> In that study, monarchs that were reared to adulthood in artificial conditions showed a reduction in navigational ability. This happened even with monarchs brought into captivity from the wild for a few days. A few captive-reared monarchs did show proper navigation. This study revealed the fragility of monarch development; if the conditions are not suitable, their ability to properly migrate could be impaired. The same study also examined the genetics of a collection of reared monarchs purchased from a butterfly breeder and found they were dramatically different from wild monarchs, so much so that the lead author described them as "franken-monarchs".<ref>{{Cite web|url=https://texasbutterflyranch.com/2019/07/02/study-of-genetic-franken-monarchs-provokes-online-ire-and-debate/|title=Study of 'genetic franken monarchs' provokes online ire and debate|last=Maeckle {{!}}|first=Monika|date=July 2, 2019 |website=texasbutterflyranch |access-date=December 12, 2019}}</ref>

An unpublished study in 2019 compared the behavior of captive-reared versus wild monarch larvae.<ref>{{Cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2019/08/10/Effects-of-captive-rearing-on-caterpillar-anti-predator-behavior---an-inside-look-at-some-preliminary-data|title=Effects of captive-rearing on caterpillar anti-predator behavior - an inside look at some preliminary data|website=monarchscience |date=August 10, 2019|access-date=December 12, 2019}}</ref> The study showed that reared larvae exhibited more defensive behavior than wild larvae. The reason for this is unknown, but it could relate to reared larvae being frequently handled and/or disturbed.

== Threats ==
In February 2015, the [[United States Fish and Wildlife Service]] (USFWS) reported a study that showed that nearly a billion monarchs had vanished from the butterfly's overwintering sites since 1990. The agency attributed the monarch's decline partly to a loss of milkweed caused by herbicides that farmers and homeowners had used.<ref>{{cite news|url = https://www.washingtonpost.com/news/energy-environment/wp/2015/08/26/nearly-a-billion-monarch-butterflies-have-vanished-now-their-haven-in-mexico-is-also-disappearing/|title = Letter: As pesticides wipe out Monarch butterflies in the U.S., illegal logging is doing the same in Mexico |date=August 26, 2015|newspaper = The Washington Post|last = Fears|first = Darryl}}</ref>

A 2017 report included mention of the new [[ethanol]]-in-gasoline standards as reducing the amount of acreage left fallow in the U.S. midwest: "Federal policies such as the Ethanol Fuel Standards ([[Renewable Fuel Standard (United States)|Renewable Fuel Standard]]), [[crop insurance]], and waning [[United States farm bill|Farm Bill]] support for [[Conservation Reserve Program|CRP]] reduce support for integrated agro-ecological landscapes capable of sustaining both food production and monarch habitat, principally because these policies promote row crops over mixed, herbaceous perennial vegetation."<ref name="ERL-2017">{{cite journal | display-authors=etal | last1=Thogmartin |first1=Wayne E |title=Restoring monarch butterfly habitat in the Midwestern US: 'all hands on deck' |journal=[[Environmental Research Letters]] |date=2017 |volume=12| issue=7 |id=074005|doi=10.1088/1748-9326/aa7637 |doi-access=free|issn=1748-9326|location=[[Bristol]], [[South West England]]|publisher=[[IOP Publishing]]| bibcode=2017ERL....12g4005T |hdl=10150/624923 |hdl-access=free }}</ref>

In 2018, a study correlated monarch butterfly decline to the fact that 95% of corn and soybean crops grown in the United States used genetically modified seeds resistant to the herbicide [[glyphosate]]. This meant that instead of spreading the herbicide only before seed planting, farmers could spread the herbicide a second time by air when weeds had begun to challenge the crops. Air application of the herbicide meant that the unplowed margins between the field and road that previously supported milkweed and a range of nectar flowers were now greatly diminished.<ref name=phys-org-2018>{{cite news |title=Florida monarch butterfly populations have dropped 80 percent since 2005 |url=https://phys.org/news/2018-11-florida-monarch-butterfly-populations-percent.html |agency=Phys.org |date=8 November 2018}}</ref>

By 2024, the USFWS calculated that the eastern butterflies had declined by approximately 80 percent since the 1980s. The western population was more imperiled, declining by 95 percent.<ref name="phys-org-monarch-2024">{{cite news |title=US moves to save once-common monarch butterflies from extinction |url=https://phys.org/news/2024-12-common-monarch-butterflies-extinction.html |agency=Phys.org |date=11 December 2024}}</ref> According to the USFWS, the species faces a host of threats, including the loss and degradation of its breeding, migratory, and overwintering habitats, exposure to [[insecticide]]s, and the growing impacts of climate change.<ref name="phys-org-monarch-2024" />

===Western monarch population===
{{further|Monarch butterfly conservation in California#Status|label1=Threats to monarch population in California|Monarch butterfly conservation in California}}
[[File:Western_monarch_populations_1997-2013.JPG|thumb|right|upright=1.3|Western monarch populations from 1997 to 2013 (from Xerces Society data)]]

Based on a 2014 20-year comparison, the overwintering numbers west of the Rocky Mountains have dropped more than 50% since 1997 and the overwintering numbers east of the Rockies have declined by more than 90% since 1995. According to the [[Xerces Society]], the monarch population in California decreased by 86% in 2018, going from millions to tens of thousands of butterflies.<ref>{{Cite web|url=https://edition.cnn.com/2019/01/07/us/monarch-butterflies-decline-trnd/index.html|title=The Monarch butterfly population in California has plummeted 86% in one year|date=January 7, 2019}}</ref>

The society's annual 2020–2021 winter count showed a significant decline in the California population. One [[Pacific Grove, California|Pacific Grove]] site had no monarch butterflies. A primary explanation for this was the destruction of the butterfly's milkweed habitats.<ref name="Xerces Society"/><ref>{{Cite web|title=Monarch butterfly population moves closer to extinction|url=https://phys.org/news/2021-01-monarch-butterfly-population-closer-extinction.html|access-date=January 21, 2021 |website=phys.org}}</ref> This particular population is believed to comprise less than 2000 individuals, {{as of|2022|lc=y}}.<ref name="Dellinger 2022">{{cite web | last=Dellinger | first=AJ | title=The monarch butterfly is endangered now, you monsters | website=Mic | date=2022-07-21 | url=https://www.mic.com/impact/monarch-butterfly-endangered | access-date=2022-07-22}}</ref>

===Eastern and midwestern monarch populations===

A 2016 study attributed the previous decade's 90% decline in overwintering numbers of the eastern monarch population primarily to the loss of breeding habitat and milkweed. The publication's authors stated that an 11%–57% probability existed that this population will become "quasi-extinct" over the next 20 years (i.e. unable to sustain a stable population).<ref name=Semmens>{{cite journal |title=Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (''Danaus plexippus'') |doi=10.1038/srep23265 |pmid=26997124 |pmc=4800428 |journal=[[Scientific Reports]] |volume=6 |article-number=23265 |year=2016 |last1=Semmens |first1=Brice X. |last2=Semmens |first2=Darius J. |last3=Thogmartin |first3=Wayne E. |last4=Wiederholt |first4=Ruscena |last5=López-Hoffman |first5=Laura |last6=Diffendorfer |first6=Jay E. |last7=Pleasants |first7=John M. |last8=Oberhauser |first8=Karen S. |last9=Taylor |first9=Orley R. |bibcode=2016NatSR...623265S}}</ref> Other threats identified in the study include climate change, insecticides, and disease.<ref name=Semmens/>

Chip Taylor, the director of [[Monarch Watch]] at the [[University of Kansas]], stated in 2013 that the Midwest milkweed habitat "is virtually gone" with 120–150{{nbsp}}million acres lost.<ref name=yale>{{cite web|url=http://e360.yale.edu/feature/tracking_the_causes_of_sharp__decline_of_the_monarch_butterfly/2634/|title=Tracking the Causes of Sharp Decline of the Monarch Butterfly|date=April 1, 2013|author=Conniff, Richard|publisher=Yale University|access-date=January 31, 2014|archive-date=December 27, 2016|archive-url=https://web.archive.org/web/20161227150305/http://e360.yale.edu/feature/tracking_the_causes_of_sharp__decline_of_the_monarch_butterfly/2634/|url-status=dead}}</ref><ref name="Wines">Wines, Michael (March 13, 2013). [https://www.nytimes.com/2013/03/14/science/earth/monarch-migration-plunges-to-lowest-level-in-decades.html "Monarch Migration Plunges to Lowest Level in Decades"]. ''The New York Times''.</ref> However, he predicted in 2024 that in the immediate future and perhaps into the next two decades, the eastern monarch butterfly population will be relatively stable because it is not presently on a continuous downward trend as it was from 2000-2006.<ref name=Taylor1/> To help fight the population decline, Monarch Watch encourages the planting of "Monarch Waystations".<ref name=watch>{{cite web|url=http://www.monarchwatch.org/class/index.htm |title=Monarch Watch|access-date=February 20, 2014 |work=[[University of Kansas]], Entomology Department|archive-url=https://web.archive.org/web/20120720103059/http://www.monarchwatch.org/class/index.htm |archive-date=July 20, 2012}}</ref>

====Habitat loss due to herbicide use and genetically modified crops====
Declines in milkweed abundance and monarch populations between 1999 and 2010 are correlated with the adoption of herbicide-tolerant [[genetically modified maize|genetically modified (GM) corn]] and soybeans, which now constitute 89% and 94% of these crops, respectively, in the U.S.<ref name=Semmens/> GM corn and soybeans are resistant to the effect of the herbicide [[glyphosate]]. Some conservationists attribute the disappearance of milkweed to agricultural practices in the [[Midwestern United States|Midwest]], where [[Genetically modified crops|GM seeds]] are bred to resist herbicides that farmers use to kill unwanted plants that grow near their rows of food crops.<ref>{{cite journal|last1=Pleasants|first1=John M.|last2=Oberhauser|first2=Karen S.|title=Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population|journal=Insect Conservation and Diversity|year=2012|url=http://www.mlmp.org/results/findings/pleasants_and_oberhauser_2012_milkweed_loss_in_ag_fields.pdf|doi=10.1111/j.1752-4598.2012.00196.x|volume=6|issue=2|pages=135–144|s2cid=14595378|archive-url=https://web.archive.org/web/20140904235825/http://www.mlmp.org/Results/Findings/Pleasants_and_Oberhauser_2012_milkweed_loss_in_ag_fields.pdf|archive-date=September 4, 2014}}</ref><ref name="Brennen">{{cite web |last=Brennen |first=Shannon |title=For Love of Nature: Annual monarch butterfly migration in peril|date=July 2014 | url= http://www.newsadvance.com/lifestyles/for-love-of-nature-annual-monarch-butterfly-migration-in-peril/article_e71ebf0e-019a-11e4-b8c9-0017a43b2370.html |publisher=The News & Advance, Lynchburg, Virginia |access-date=July 4, 2014}}</ref>

In 2015, the [[Natural Resources Defense Council]] filed a suit against the [[United States Environmental Protection Agency]] (EPA). The Council argued that the agency ignored warnings about the dangers of glyphosate usage for monarchs.<ref>{{cite web|title=NRDC Sues EPA Over Demise of Monarch Butterfly Population|url=https://www.nbcnews.com/science/environment/nrdc-sues-epa-over-demise-monarch-butterfly-population-n314371|year=2015|publisher=NBC}}</ref> However, a 2018 study has suggested that the decline in milkweed predates the arrival of GM crops.<ref>{{Cite journal|last1=Puzey|first1=J. R.|last2=Dalgleish|first2=H. J.|last3=Boyle|first3=J. H.|date=February 5, 2019 |title=Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops|journal=Proceedings of the National Academy of Sciences of the United States of America |volume=116 |issue=8|pages=3006–3011|doi=10.1073/pnas.1811437116|issn=0027-8424|pmid=30723147|pmc=6386695|bibcode=2019PNAS..116.3006B |doi-access=free}}</ref>

====Losses during migration====
Eastern and midwestern monarchs are experiencing problems reaching Mexico. Many monarch researchers have cited recent evidence from long-term citizen science data that shows that the number of breeding (adult) monarchs has not declined in the last two decades.<ref name="Ries 2015">{{cite journal|doi=10.1093/aesa/sav055|title=The Disconnect Between Summer and Winter Monarch Trends for the Eastern Migratory Population: Possible Links to Differing Drivers|journal=Annals of the Entomological Society of America|volume=108|issue=5|page=691|year=2015|last1=Ries|first1=Leslie|last2=Taron|first2=Douglas J.|last3=Rendón-Salinas|first3=Eduardo|s2cid=85597731}}</ref><ref name="Inamine 2016">{{cite journal|doi=10.1111/oik.03196|title=Linking the continental migratory cycle of the monarch butterfly to understand its population decline |journal=[[Oikos (journal)|Oikos]] |volume=125 |issue=8 |page=1081 |year=2016 |last1=Inamine |first1=Hidetoshi |last2=Ellner |first2=Stephen P.|last3=Springer|first3=James P.|last4=Agrawal|first4=Anurag A.|doi-access=free|bibcode=2016Oikos.125.1081I }}</ref><ref name="ReferenceA">{{cite journal|doi=10.1111/j.1752-4598.2011.00158.x|title=Are migratory monarchs really declining in eastern North America? Examining evidence from two fall census programs|journal=Insect Conservation and Diversity|volume=5|issue=2|page=101|year=2012|last1=Davis|first1=Andrew K.|s2cid=54038257|doi-access=free}}</ref>

The lack of long-term declines in the numbers of breeding and migratory monarchs, yet the clear declines in overwintering numbers, suggests a growing disconnect exists between these life stages. One researcher has suggested that mortality from car strikes constitutes an increasing threat to migrating monarchs.<ref name="monarchscience">{{cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2016/08/24/Is-road-mortality-the-real-cause-of-the-decline-in-Mexico |title=monarchscience |publisher=Akdavis6.wixsite.com |date=August 24, 2016 |access-date=January 6, 2017}}</ref> A study of road mortality in northern Mexico, published in 2019, showed very high mortality from just two "hotspots" each year, amounting to 200,000 monarchs killed.<ref>{{Cite journal|last1=Mora Alvarez|first1=Blanca Xiomara|last2=Carrera-Treviño|first2=Rogelio|last3=Hobson|first3=Keith A.|date=2019|title=Mortality of Monarch Butterflies (''Danaus plexippus'') at Two Highway Crossing "Hotspots" During Autumn Migration in Northeast Mexico|journal=Frontiers in Ecology and Evolution |volume=7|article-number=273 |doi=10.3389/fevo.2019.00273|bibcode=2019FrEEv...7..273M |issn=2296-701X|doi-access=free}}</ref>

====Importance of overwintering habitat====
[[File:Danaus plexippus overwintering area 2018.png|thumb|Area covered by monarchs (''D. plexippus'', eastern migratory population) in their overwintering areas in Mexico between 1993 and 2018]]
The area of Mexican forest to which eastern and midwestern monarchs migrate reached its lowest level in two decades in 2013. The decline was expected to increase during the 2013–2014 season. Mexican environmental authorities continue to monitor [[illegal logging]] of the [[Abies religiosa|oyamel fir trees]]; however, organized criminals have repeatedly crushed such efforts in the name of very short-term financial gain.<ref>{{cite web |last=Guadarrama |first=Ricardo |date=January 12, 2024 |url=https://www.elfinanciero.com.mx/estados/2024/01/12/crimen-organizado-y-tala-ilegal-ahuyentan-a-la-mariposa-monarca-en-jiquipilco-edomex/ |title=Crimen organizado y tala ilegal ahuyentan a la mariposa monarca en Jiquipilco, Edomex |work=[[El Financiero]] |archive-url=https://web.archive.org/web/20240112174731/https://www.elfinanciero.com.mx/estados/2024/01/12/crimen-organizado-y-tala-ilegal-ahuyentan-a-la-mariposa-monarca-en-jiquipilco-edomex/ |archive-date=January 12, 2024}}</ref> The oyamel is a major species of evergreen on which the overwintering butterflies spend a significant time during their winter [[diapause]], or suspended development.<ref>Paz, Fátima (June 18, 2014). [http://www.cambiodemichoacan.com.mx/nota-227099 "En espera de aprobación de la Profepa por tala ilegal en la Reserva de la Mariposa Monarca"] {{Webarchive|url=https://web.archive.org/web/20140903143808/http://www.cambiodemichoacan.com.mx/nota-227099 |date=September 3, 2014}}. ''cambiodemichoacan.com.mx''.</ref>

A 2014 study acknowledged that while "the protection of overwintering habitat has no doubt gone a long way towards conserving monarchs that breed throughout eastern North America", their research indicates that habitat loss on breeding grounds in the United States is the main cause of recent and projected population declines.<ref name="University of Guelph">{{cite web | url=http://www.uoguelph.ca/news/2014/06/habitat_loss_on.html | title=Habitat Loss on Breeding Grounds Cause of Monarch Decline, U of G Study Finds | publisher=University of Guelph |date=June 4, 2014 | access-date=March 17, 2015}}</ref>

Western monarch populations have rebounded slightly since 2014 with the Western Monarch Thanksgiving Count <ref>{{Cite web |date=2023-02-01 |title=Western Monarch Population Rebound Continues in 2022 but Winter Storms Could Impact Spring Breeding Population |url=https://farmersformonarchs.org/western-monarch-population-rebound-continues-in-2022-but-winter-storms-could-impact-spring-breeding-population/ |access-date=2023-04-14 |website=Farmers for Monarchs}}</ref> tallying 335,479 monarchs in 2022. The population still has much to go for a full recovery.

=== Parasites ===
[[File:Monarch chrysalis - Danaus plexippus and Pteromalid Wasp, Meadowood Farm SRMA, Mason Neck, Virginia - 29789548882.jpg|thumb|upright|''[[Pteromalus cassotis]]'' on monarch chrysalis]]
Parasites include the [[Tachinidae|tachinid flies]] ''[[Sturmia convergens]]'',<ref>{{cite journal |last=Clarke |first= A. R. |author2=Zalucki, M. P. |year=2001 |title= ''Taeniogonalos raymenti'' Carmean & Kimsey (Hymenoptera: Trigonalidae) reared as a hyperparasite of ''Sturmia convergens'' (Weidemann) (Diptera: Tachinidae), a primary parasite of ''Danaus plexippus'' (L.) (Lepidoptera: Nymphalidae) |journal=Pan-Pacific Entomologist |volume=77 |issue=2 |pages=68–70|url=https://www.biodiversitylibrary.org/page/56142301#page/74/mode/1up }}</ref> ''[[Compsilura concinnata]]'',<ref name=Oberhauser>{{cite journal|first1=Karen|last1=Oberhauser|first2=Dane|last2=Elmquist|first3=Juan Manuel|last3=Perilla-Lopez|first4=Ilse|last4=Gebhard|first5=Laura|last5=Lukens|first6=John|last6=Stireman|date=November 2017|url=https://stiremanlab.org/wp-content/uploads/2018/08/oberhauser-et-al-2017-tachinid-parasites-in-monarchs.pdf|title=Tachinid Fly (Diptera: Tachinidae) Parasitoids of Danaus plexippus (Lepidoptera: Nymphalidae)|journal=[[Annals of the Entomological Society of America]]|volume=110|issue=6|pages=536–543|doi=10.1093/aesa/sax048|publisher=[[Oxford University Press]]|access-date=January 6, 2025|archive-url=https://web.archive.org/web/20241228124906/https://stiremanlab.org/wp-content/uploads/2018/08/oberhauser-et-al-2017-tachinid-parasites-in-monarchs.pdf|archive-date=December 28, 2024|url-status=live}}</ref> ''[[Madremyia saundersii]]'',<ref name=Oberhauser/> ''Hyphantrophaga virilis'',<ref name=Oberhauser/> ''Nilea erecta'',<ref name=Oberhauser/> and ''[[Lespesia archippivora]]''.<ref name=Oberhauser/>  ''Lespesia''-parasitized butterfly larvae suspend, but die prior to [[pupa]]tion. The fly's maggot lowers to the ground, forms a brown [[puparium]], and then emerges as an adult.<ref name = Brewer>{{cite journal |last=Brewer |first=Jo |author2=Gerard M. Thomas |year=1966 |title=Causes of death encountered during rearing of ''Danaus plexippus'' (Danaidae) |journal=Journal of the Lepidopterists' Society |volume=20 |issue=4 |pages=235–238 |archive-url=https://web.archive.org/web/20090325051238/http://research.yale.edu/peabody/jls/pdfs/1960s/1966/1966-20%284%29235-Brewer.pdf|archive-date=March 25, 2009|url=http://research.yale.edu/peabody/jls/pdfs/1960s/1966/1966-20(4)235-Brewer.pdf |access-date=April 13, 2008}}</ref>

[[Pteromalidae|Pteromalid wasps]], specifically ''[[Pteromalus cassotis]]'', parasitize monarch pupae.<ref name="pteromalidae">{{cite journal|last1=Stenoien|first1=Carl|last2=McCoshum|first2=Shaun|last3=Caldwell|first3=Wendy|last4=De Anda|first4=Alma|last5=Oberhauser|first5=Karen|title=New reports that Monarch butterflies (Lepidoptera: Nymphalidae, Linnaeus) are hosts for a pupal parasitoid (Hymenoptera: Chalcidoidea, Walker)|journal=[[Journal of the Kansas Entomological Society]] |date=January 2015|volume=88|issue=1|pages=16–26|doi=10.2317/JKES1402.22.1|s2cid=52231552}}</ref> These wasps lay their eggs in the pupae while the chrysalis is still soft. Up to 400 adults emerge from the chrysalis after 14–20 days,<ref name="pteromalidae" /> killing the monarch.

The bacterium ''[[Micrococcus]] flacidifex danai'' also infects larvae. Just before pupation, the larvae migrate to a horizontal surface and die a few hours later, attached only by one pair of prolegs, with the thorax and abdomen hanging limp. The body turns black shortly thereafter. The bacterium ''[[Pseudomonas aeruginosa]]'' has no invasive powers, but causes [[secondary infection]]s in weakened insects. It is a common cause of death in laboratory-reared insects.<ref name = Brewer/>

''Ophryocystis elektroscirrha'' is another parasite of the monarch. It infects the [[subcutaneous tissue]]s and propagates by spores formed during the pupal stage. The spores are found over all of the bodies of infected butterflies, with the greatest number on the abdomen. These spores are passed, from [[vertical transmission|female to caterpillar]], when spores rub off during egg laying and are then ingested by caterpillars. Severely infected individuals are weak, unable to expand their wings, or unable to eclose, and have shortened lifespans, but parasite levels vary in populations. This is not the case in laboratory rearing, where after a few generations, all individuals can be infected.<ref>{{cite journal |last=Leong |first= K. L. H. |author2=M. A. Yoshimura, H. K. Kaya and H. Williams |year=1997 |title= Instar susceptibility of the Monarch butterfly (''Danaus plexippus'') to the neogregarine parasite, ''Ophryocystis elektroscirrha'' |journal=[[Journal of Invertebrate Pathology]] |volume=69 |issue=1 |pages=79–83 |doi=10.1006/jipa.1996.4634 |pmid=9028932|bibcode= 1997JInvP..69...79L |citeseerx= 10.1.1.494.9827}}</ref>

Infection with ''O. elektroscirrha'' creates an effect known as [[culling]], whereby migrating monarchs that are infected are less likely to complete the migration. This results in overwintering populations with lower parasite loads.<ref name="Bartel Ober">{{cite journal|last1=Bartel|first1=Rebecca|last2=Oberhauser|first2=Karen|last3=De Roode|first3=Jacob|last4=Atizer|first4=Sonya|title=Monarch butterfly migration and parasite transmission in eastern North America|journal=[[Ecology (journal)|Ecology]] |date=February 2011 |volume=92|issue=2|pages=342–351|doi=10.1890/10-0489.1|pmid=21618914|pmc=7163749|bibcode=2011Ecol...92..342B }}</ref> Owners of commercial butterfly-breeding operations claim that they take steps to control this parasite in their practices,<ref>{{cite web | title = Do My Monarch Butterflies Have OE? ''Ophryocystis elektroscirrha'' | publisher = Butterfly Fun Facts | url = http://www.butterfly-fun-facts.com/disease-oe/oe-ophryocystis-elektroscirrha-monarch-butterfly/do-my-monarch-butterflies-have-oe-ophryocystis-elektroscirrha/ | access-date = March 24, 2015 | archive-date = March 4, 2015 | archive-url = https://web.archive.org/web/20150304091537/http://www.butterfly-fun-facts.com/disease-oe/oe-ophryocystis-elektroscirrha-monarch-butterfly/do-my-monarch-butterflies-have-oe-ophryocystis-elektroscirrha/ }}</ref> although this claim is doubted by many scientists who study monarchs.<ref>{{Cite book|last1=Jepsen|first1=S.|title=Conservation Status and Ecology of the Monarch Butterfly in the United States|last2=Schweitzer|first2=D. F.|last3=Young|first3=B.|last4=Sears|first4=N.|last5=Ormes|first5=M.|last6=Black|first6=S. H.|publisher=NatureServe|year=2015|pages=23–24}}</ref>

=== Confusion of host plants ===
The black swallow-wort (''[[Cynanchum louiseae]]'') and pale swallow-wort (''[[Cynanchum rossicum]]'') plants are problematic for monarchs in North America. Monarchs lay their eggs on these relatives of native vining milkweed (''[[Cynanchum laeve]]'') because they produce stimuli similar to milkweed. Once the eggs hatch, the caterpillars are poisoned by the toxicity of this [[invasive plant]] from Europe.<ref>[http://monarchjointventure.org/images/uploads/documents/Swallow-wort_flyer.pdf Invasive species alert: Black swallow-wort (''Cynanchum louisea'') and pale swallow-wort (''Cynanchum rossicum'')] {{Webarchive|url=https://web.archive.org/web/20210916203741/http://monarchjointventure.org/images/uploads/documents/Swallow-wort_flyer.pdf |date=September 16, 2021}}. monarchjointventure.org</ref>

=== Climate ===
Climate variations during the fall and summer affect butterfly reproduction. Rainfall and freezing temperatures affect milkweed growth. Omar Vidal, director general of WWF-Mexico, said, "The monarch's lifecycle depends on the climatic conditions in the places where they breed. Eggs, larvae, and pupae develop more quickly in milder conditions. Temperatures above {{cvt|35|C|F}} can be lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate."<ref>{{cite web|url=http://worldwildlife.org/stories/monarch-population-hits-lowest-point-in-more-than-20-years|title=Monarch Population Hits Lowest Point in More Than 20 Years|work=World Wildlife Fund |date=January 29, 2014|location=Washington, D.C.|publisher=[[World Wildlife Fund]]|access-date=October 12, 2021|archive-url=https://web.archive.org/web/20210225072001/http://worldwildlife.org/stories/monarch-population-hits-lowest-point-in-more-than-20-years|archive-date=February 25, 2021|url-status=live}}</ref> If a monarch's body temperatures is below {{cvt|30|C|F}}, a monarch cannot fly. To warm up, they sit in the sun or rapidly shiver their wings to warm themselves.<ref>{{Cite web |url=http://www.defenders.org/monarch-butterfly/basic-facts |title=Basic Facts About Monarch Butterflies|date=January 9, 2020}}</ref>

[[Climate change]] may dramatically affect the monarch migration. A study from 2015 examined the impact of warming temperatures on the breeding range of the monarch and showed that in the next 50 years, the monarch host plant will expand its range further north into Canada and that the monarchs will follow this.<ref>{{cite journal|doi=10.1371/journal.pone.0118614|pmid=25705876|pmc=4338007|title=Climate Change May Alter Breeding Ground Distributions of Eastern Migratory Monarchs (''Danaus plexippus'') via Range Expansion of ''Asclepias'' Host Plants|journal=[[PLOS One]] |volume=10|issue=2|article-number=e0118614|year=2015|last1=Lemoine|first1=Nathan P.|bibcode=2015PLoSO..1018614L|doi-access=free}}</ref> While this will expand the breeding locations of the monarch, it will also have the effect of increasing the distance that monarchs must travel to reach their overwintering destination in Mexico, which could result in greater mortality during the migration.<ref>{{cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2015/08/10/The-quietlypublished-paper-on-climate-change-and-monarchs |title=monarchscience |publisher=Akdavis6.wixsite.com |date=August 10, 2015}}</ref>

Milkweeds grown at increased temperatures have been shown to contain higher cardenolide concentrations, making the leaves too toxic for the monarch caterpillars. However, these increased concentrations are likely in response to increased insect herbivory, which is also caused by the increased temperatures. Whether increased temperatures make milkweed too toxic for monarch caterpillars when other factors are not present is unknown.<ref>{{Cite journal|last1=Hahn|first1=Philip G.|last2=Agrawal|first2=Anurag A.|last3=Sussman|first3=Kira I.|last4=Maron|first4=John L.|date=January 2019|title=Population Variation, Environmental Gradients, and the Evolutionary Ecology of Plant Defense against Herbivory|journal=The American Naturalist|volume=193|issue=1|pages=20–34|doi=10.1086/700838|issn=1537-5323|pmid=30624107|bibcode=2019ANat..193...20H |s2cid=54076888}}</ref> Additionally, milkweed grown at carbon dioxide levels of 760 parts per million was found to produce a different mix of the toxic cardenolides, one of which was less effective against monarch parasites.<ref name="Climate change, pesticides put monarch butterflies at risk of extinction">{{cite web | title = Climate change, pesticides put monarch butterflies at risk of extinction | publisher=National Geographic | url =https://www.nationalgeographic.com/animals/2018/12/monarch-butterflies-risk-extinction-climate-change/ | archive-url =https://web.archive.org/web/20181223064901/https://www.nationalgeographic.com/animals/2018/12/monarch-butterflies-risk-extinction-climate-change/ | archive-date =December 23, 2018 |access-date=December 31, 2018 |date=December 21, 2018}}</ref>

== Conservation status ==

The number of monarchs overwintering in Mexico has shown a long-term downward trend. Since 1995, coverage numbers have been as high as {{convert|18|ha|acre|0}} during the winter of 1996–1997, but on average about {{convert|6|ha|acre|0}}. Coverage declined to its lowest point to date ({{convert|0.67|ha|acre|2}}) during the winter of 2013–2014, but rebounded to {{convert|4.01|ha|acre|0}} in 2015–2016. The average population of monarchs in 2016 was estimated at 200{{nbsp}}million. Historically, on average there are 300{{nbsp}}million monarchs. The 2016 increase was attributed to favorable breeding conditions in the summer of 2015. However, coverage declined by 27% to {{convert|2.91|ha|acre|2}} during the winter of 2016–2017. Some believe this was because of a storm that had occurred during March 2016 in the monarchs' previous overwintering season.<ref>Multiple sources:
* {{cite web|archive-url=https://web.archive.org/web/20160228234901/http://www.learner.org/jnorth/monarch/spring2016/05/monarch-butterfly-population-size.html|archive-date=February 28, 2016|url=http://www.learner.org/jnorth/monarch/spring2016/05/monarch-butterfly-population-size.html|work=Journey North|title=Monarch Population Size Announced|date=February 26, 2016|last=Howard|first=Elizabeth|access-date=June 6, 2017}} 
* {{cite web|archive-url=https://web.archive.org/web/20240623102928/https://monarchjointventure.org/blog/eastern-monarch-population-numbers-drop-27 |archive-date=June 23, 2024|url=https://monarchjointventure.org/blog/eastern-monarch-population-numbers-drop-27|title=Eastern Monarch Population Numbers Drop 27%|work=News|publisher=The Monarch Joint Venture|date=February 16, 2017|access-date=January 5, 2024|url-status=live}}
* {{cite web|archive-url=https://web.archive.org/web/20160822070321/http://monarchlab.org/resources-links/blog/where-are-all-the-monarchs|archive-date=August 22, 2016|url=http://monarchlab.org:80/resources-links/blog/where-are-all-the-monarchs|title=Where Are All The Monarchs?|work=Monarch Lab|publisher=[[University of Minnesota]] Extension|date=July 14, 2016|access-date=June 5, 2017}}</ref> However, this seems unlikely since most current research shows that the overwintering colony sizes do not predict the size of the next summer breeding population.<ref>{{Cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2019/11/04/Another-monarch-study-published-showing-the-spring-migration-holds-the-key-to-everything|title=Another monarch study published showing the spring migration holds the key to everything|website=monarchscience |date=November 4, 2019|access-date=January 5, 2025|archive-url=https://web.archive.org/web/20240518102521/https://www.monarchscience.org/single-post/2019/11/04/Another-monarch-study-published-showing-the-spring-migration-holds-the-key-to-everything|archive-date=May 18, 2024|url-status=live}}</ref>

On July 20, 2022, the [[International Union for Conservation of Nature]] added the migratory monarch butterfly (the subspecies common in North America) to its [[IUCN Red List|red list]] as an endangered species.<ref name="Larson">{{cite web |last1=Larson |first1=Christina |title=Beloved monarch butterflies now listed as endangered |url=https://apnews.com/article/science-north-america-insects-butterflies-climate-and-environment-c5e406e2f01c731167393296c19c302b |website=AP News |access-date=January 5, 2024 |language=en |date=July 21, 2022|archive-url=https://web.archive.org/web/20240929115921/https://apnews.com/article/science-north-america-insects-butterflies-climate-and-environment-c5e406e2f01c731167393296c19c302b|archive-date=September 29, 2024|url-status=live}}</ref> However, a petition in 2023 resulted in its status being changed to "vulnerable".<ref name="IUCN"/>

The monarch butterfly is not listed under the [[CITES|Convention on International Trade in Endangered Species of Wild Fauna and Flora]] or protected specifically under U.S. domestic laws.<ref name="fws.gov" />

On August 14, 2014, the Center for Biological Diversity and the [[Center for Food Safety]] petitioned the [[United States Secretary of the Interior]] through the USFWS to protect the ''Danaus plexippus plexippus'' subspecies of the monarch butterfly as a threatened species under the [[Endangered Species Act]].<ref name="Xerces Society"/> On December 31, 2014, the USFWS initiated a review of the status of the butterfly to determine whether the petitioned action was warranted, with a due date for the submission of information of March 3, 2015, later extended to December 15, 2020.<ref>Multiple sources:
* {{cite journal|author=U.S. Fish and Wildlife Service|date=December 31, 2014|title=Endangered and Threatened Wildlife and Plants; 90-Day Findings on Two Petitions|journal=[[Federal Register]]|id=Federal Register Document Number 2014-30574|volume=79|number=250|pages=78775–78778|access-date=January 4, 2025|url=https://www.govinfo.gov/content/pkg/FR-2014-12-31/pdf/2014-30574.pdf|archive-url=https://web.archive.org/web/20240630205357/https://www.govinfo.gov/content/pkg/FR-2014-12-31/pdf/2014-30574.pdf|archive-date=June 30, 2024|url-status=live}}
* {{cite web|date=June 2021|title=Endangered species listing for the monarch butterfly: What private landowners need to know|url=https://farmersformonarchs.org/wp-content/uploads/2021/06/ESA-101-for-landowners-revised-with-proposed-decision-011221.pdf|location=[[Keystone, Colorado]]|publisher=Keystone Policy Center|archive-url=https://web.archive.org/web/20240620070812/https://farmersformonarchs.org/wp-content/uploads/2021/06/ESA-101-for-landowners-revised-with-proposed-decision-011221.pdf|archive-date=June 20, 2024|url-status=live}}</ref>

On December 17, 2020, the USFWS published in the [[Federal Register]] a notice in which it stated that adding the butterfly to the list of [[Endangered Species Act#Two categories for listing species|threatened and endangered species]] was "[[Endangered Species Act#Listing process|warranted-but-precluded]]" because budgetary limitations required it to devote its resources to species with [[Endangered Species Act#Citizens can petition for listing species|higher priorities]] for [[Endangered Species Act#Five criteria for making listing decisions|listing]]. The notice stated that the USFWS had 422 [[Endangered Species Act#Listing process|12-month petition]] findings for domestic species yet to be initiated and completed at the beginning of [[Fiscal Year]] 2020 (October 1, 2019).<ref>Multiple sources:
* {{cite journal|author=U.S. Fish and Wildlife Service|date=December 17, 2020|title=Endangered and Threatened Wildlife and Plants; 12-Month Finding for the Monarch Butterfly|journal=[[Federal Register]]|id=Federal Register Document Number 2020-27523|volume=85|number=243|pages=78775–78778|access-date=January 5, 2025|url=https://www.govinfo.gov/content/pkg/FR-2020-12-17/pdf/2020-27523.pdf|archive-url=https://web.archive.org/web/20240928225703/https://www.govinfo.gov/content/pkg/FR-2020-12-17/pdf/2020-27523.pdf|archive-date=September 28, 2024|url-status=live}}
* {{cite news|first=Rachel|last=Frazin|date=December 15, 2021|url=https://thehill.com/policy/energy-environment/530298-trump-administration-punts-on-protections-for-monarch-butterfly|title=Trump administration punts on protections for monarch butterfly|work=[[The Hill (newspaper)|The Hill]]|access-date=October 6, 2021|archive-url=https://web.archive.org/web/20211001041825/https://thehill.com/policy/energy-environment/530298-trump-administration-punts-on-protections-for-monarch-butterfly|archive-date=October 1, 2021|url-status=live|quote=The Fish and Wildlife Service (FWS) determined that adding the butterfly to the list of threatened and endangered species was "warranted", but that it is unable to do so because it needs to devote its resources to higher-priority species. The FWS said that its "warranted-but-precluded" determination means that every year it will consider adding the butterfly to the list until it decides to propose listing it or determines that protections are not warranted.}}
* {{cite web|title=What is the fiscal year?|year=2024|url=https://www.xero.com/us/glossary/fiscal-year/|publisher=[[Xero (company)|Xero Limited]]|access-date=January 16, 2025|quote=Fiscal years are named using the year when the period ends. For example, the US federal government fiscal year starts on October 1, 2024 and ends on September 30, 2025; this is referred to as FY25.|archive-url=https://web.archive.org/web/20241004114900/https://www.xero.com/us/glossary/fiscal-year/|archive-date=October 4, 2024|url-status=live}}</ref>

On June 27, 2023, the USFWS published in the Federal Register a [[Notice of proposed rulemaking|Notice of Proposed Rulemaking]] for a rule that would give the butterfly a listing priority number (LPN) of 8 for adding its species to that list.<ref>Multiple sources:
* {{cite journal|author=U.S. Fish and Wildlife Service|date=June 27, 2023|title=Endangered and Threatened Wildlife and Plants; Review of Species That Are Candidates for Listing as Endangered or Threatened; Annual Notification of Findings on Resubmitted Petitions; Annual Description of Progress on Listing Actions|journal=[[Federal Register]]|id=Federal Register Document Number 2023-13577|volume=88|number=122|pages=41560–41580|access-date=September 29, 2024|url=https://www.govinfo.gov/content/pkg/FR-2023-06-27/pdf/2023-13577.pdf|archive-url=https://web.archive.org/web/20230627081856/https://www.govinfo.gov/content/pkg/FR-2023-06-27/pdf/2023-13577.pdf |archive-date=June 27, 2023|url-status=live}}
* Ibid., Monarch Butterfly, p. 41570.</ref> LPNs range from 1 to 12 (the lower the LPN, the higher the listing priority).<ref>Ibid., Previous CNORs, p. 41561. "We have been publishing CNORs since 1975. The most recent was published on May 3, 2022 (87 FR 26152). On September 21, 1983, we published guidance for assigning a listing priority number (LPN) for each candidate species (48 FR 43098). Using this guidance, we assign each candidate an LPN of 1 to 12, depending on the magnitude of threats, immediacy of threats, and taxonomic status; the lower the LPN, the higher the listing priority (that is, a species with an LPN of 1 would have the highest listing priority)."</ref>

On December 12, 2024, the USFWS published in the Federal Register a proposed rule that would list the monarch butterfly (''Danaus plexippus'') as a threatened species and would designate the butterfly's [[critical habitat]] per the provisions of the Endangered Species Act. The USFWS estimated in the proposed rule that the probability of extinction in the foreseeable future (60 years) is 56-74 percent for the eastern monarch migratory population and 99 percent for the western migratory population. The proposed rule designated seven areas near California's [[West Coast of the United States|Pacific coast]] as "critical habitat units" for monarch butterflies. The USFWS accepted comments on the proposed rule until March 12, 2025.<ref>{{cite journal|author=U.S. Fish and Wildlife Service|date=December 12, 2024|title=Endangered and Threatened Wildlife and Plants; Threatened Species Status With Section 4(D) Rule for Monarch Butterfly and Designation of Critical Habitat|journal=[[Federal Register]]|id=Federal Register Document Number 2024-20855|volume=89|number=239|pages=100662–100716|access-date=January 5, 2025|url=https://www.govinfo.gov/content/pkg/FR-2024-12-12/pdf/2024-28855.pdf|archive-url=https://web.archive.org/web/20241226042937/https://www.govinfo.gov/content/pkg/FR-2024-12-12/pdf/2024-28855.pdf|archive-date=December 26, 2024|url-status=live}}</ref> On March 19, 2025, the USFWS reopened the comment period on the proposed rule until May 19, 2025.<ref>{{cite journal|author=U.S. Fish and Wildlife Service|date=March 19, 2025|title=Endangered and Threatened Wildlife and Plants; Reopening Comment Periods for Three Proposed Rules; Announcement of a Public Hearing for One Proposed Rule|journal=[[Federal Register]]|id=Federal Register Document Number 2025–04443|volume=90|number=52|pages=12694–12695|access-date=May 12, 2025|url=https://www.govinfo.gov/content/pkg/FR-2025-03-19/pdf/2025-04443.pdf|archive-url=https://web.archive.org/web/20250319185128/https://www.govinfo.gov/content/pkg/FR-2025-03-19/pdf/2025-04443.pdf|archive-date=March 19, 2025|url-status=live}}</ref> 

In December 2023, the [[Government of Canada]] listed the monarch as an endangered species under the federal [[Species at Risk Act]]. The listing protects the butterfly on Canadian federal lands by making it illegal to kill, hurt, catch or remove a monarch egg, caterpillar, chrysalis or adult when on land that the Canadian federal government owns and/or administers. These include Canadian [[National parks of Canada|national parks]], [[National Wildlife Area|national wildlife area]]s, [[Canadian Forces base|military base]]s and [[Indian reserve|First Nations reserve]]s. It is also illegal to possess, collect, buy, sell, or trade an individual monarch or any part or derivative of an individual when on that land. The Canadian government must prepare a recovery strategy and one or more action plans for the species to outline the work that can be done to conserve the species. The strategy must identify the critical habitat necessary for the monarch to survive and recover in Canada.<ref>{{cite web|title=Monarch Butterfly: profile of a species at risk|url=https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/factsheets/monarch-butterfly.html|date=February 18, 2025|publisher=[[Environment and Climate Change Canada]], [[Government of Canada]]|access-date=March 14, 2025|archive-url=https://web.archive.org/web/20250310121724/https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/factsheets/monarch-butterfly.html|archive-date=March 10, 2025|url-status=live}}</ref> 
 
In [[Ontario]], Canada, the monarch butterfly is listed as a species of special concern.<ref name="Monarch Butterfly Status in Ontario"/>  In [[Nova Scotia]], the monarch is listed as endangered at the provincial level, {{as of|2017|lc=y}}. This decision (as well as the Ontario decision) is based on a presumption that the overwintering colony declines in Mexico create declines in the breeding range in Canada.<ref>{{Cite web|url=http://akdavis6.wixsite.com/monarchscience/single-post/2019/09/30/Monarchs-now-listed-as-an-endangered-species-in-Nova-Scotia-Canada---a-prelude-for-things-to-come-elsewhere|title=Monarchs now listed as an endangered species in Nova Scotia Canada - a prelude for things to come elsewhere|website=monarchscience |date=September 30, 2019|access-date=December 12, 2019}}</ref> Two recent studies have been conducted examining long-term trends in monarch abundance in Canada, using either butterfly atlas records<ref>{{Cite journal|last1=Crewe|first1=Tara L.|last2=Mitchell|first2=Greg W.|last3=Larrivée|first3=Maxim|date=2019|title=Size of the Canadian Breeding Population of Monarch Butterflies Is Driven by Factors Acting During Spring Migration and Recolonization|journal=Frontiers in Ecology and Evolution |volume=7|article-number=308 |doi=10.3389/fevo.2019.00308|bibcode=2019FrEEv...7..308C |issn=2296-701X|doi-access=free}}</ref> or citizen science butterfly surveys,<ref>{{Cite journal|last1=Flockhart|first1=D. T. Tyler|last2=Larrivée|first2=Maxim|last3=Prudic|first3=Kathleen L.|last4=Norris|first4=D. Ryan|date=June 21, 2019 |title=Estimating the annual distribution of monarch butterflies in Canada over 16 years using citizen science data|journal=FACETS|volume=4|issue=1 |pages=238–253 |doi=10.1139/facets-2018-0011|doi-access=free|bibcode=2019Facet...4..238T |hdl=10150/633480|hdl-access=free}}</ref> and neither shows evidence of a population decline in Canada.

==Conservation efforts==
{{see also|Monarch butterfly conservation in California}}
Although the numbers of breeding monarchs in eastern North America have not decreased, reports of declining numbers of overwintering butterflies have inspired efforts to conserve the species.<ref name="Ries 2015"/><ref name="Inamine 2016"/><ref name="ReferenceA"/>

===Federal actions===
On June 20, 2014, President [[Barack Obama]] issued a presidential memorandum entitled "Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators". The memorandum established a Pollinator Health Task Force, to be co-chaired by the [[United States Secretary of Agriculture|Secretary of Agriculture]] and the [[Administrator of the Environmental Protection Agency]], and stated:

{{blockquote|The number of migrating Monarch butterflies sank to the lowest recorded population level in 2013–14, and there is an imminent risk of failed migration.<ref>{{cite web|last=Obama|first=President Barack|url=https://obamawhitehouse.archives.gov/the-press-office/2014/06/20/presidential-memorandum-creating-federal-strategy-promote-health-honey-b|title=Presidential Memorandum – Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators|date=June 20, 2014 |work=Office of the Press Secretary|location=Washington, D.C.|publisher=[[White House|The White House]]|access-date=May 2, 2018}}</ref>}}

The U.S. [[General Services Administration]] (GSA) publishes sets of landscape performance requirements in its P100 documents, which mandate standards for the GSA's [[General Services Administration#Federal property and buildings|Public Buildings Service]]. Beginning in March 2015, those performance requirements and their updates have included four primary aspects for planting designs that are intended to provide adequate on-site [[foraging]] opportunities for targeted pollinators. The targeted pollinators include bees, butterflies, and other beneficial insects.<ref>Multiple sources:
* {{cite web|url=https://www.gsa.gov/system/files/2015_P100_FacilitiesStandards.pdf|title=PBS-P100 Facilities Standards For The Public Buildings Service|work=[[Whole Building Design Guide|WBDG: Whole Building Design Guide]]|date=March 1, 2015|page=12|location=Washington, D.C.|publisher=[[National Institute of Building Sciences]]|access-date=January 8, 2024|archive-url=https://web.archive.org/web/20240108172838/https://www.gsa.gov/system/files/2015_P100_FacilitiesStandards.pdf|archive-date=January 8, 2024|quote=The P100 is a mandatory standard. It is not a guideline, textbook, handbook, training manual, or substitute for technical competence. The P100 represents the current state of practice in designing facilities to meet GSA's commitments, maximize the efficiency of business processes, and comply with the requirements of law.}}
* {{cite web|url=https://www.gsa.gov/system/files/2015_P100_FacilitiesStandards.pdf|title=PBS-P100: Facilities Standards for the Public Buildings Service|work=Landscape Requirements|date=March 1, 2015|pages=40–47|location=Washington, D.C.|publisher=[[General Services Administration|U.S. General Services Administration]]|access-date=January 8, 2024|archive-url=https://web.archive.org/web/20240108172838/https://www.gsa.gov/system/files/2015_P100_FacilitiesStandards.pdf|archive-date=January 8, 2024}}</ref>

In May 2015, the Pollinator Health Task Force issued a "National Strategy to Promote the Health of Honey Bees and Other Pollinators". The strategy laid out federal actions to achieve three goals, two of which were:

{{blockquote|
* Monarch Butterflies: Increase the Eastern population of the monarch butterfly to 225 million butterflies occupying an area of approximately {{convert|15|acre|ha|abbr=off}} in the overwintering grounds in Mexico, through domestic/international actions and public-private partnerships, by 2020.
* Pollinator Habitat Acreage: Restore or enhance 7 million acres of land for pollinators over the next 5 years through Federal actions and public/private partnerships.<ref name=strategy>{{cite web|author=Pollinator Health Task Force|url=https://obamawhitehouse.archives.gov/sites/default/files/microsites/ostp/Pollinator%20Health%20Strategy%202015.pdf|title=National Strategy to Promote the Health of Honey Bees and Other Pollinators|location=Washington, D.C.|publisher=[[The White House]]|date=May 19, 2015 |access-date=May 2, 2018}}</ref><ref name=Newswire>{{cite news|author=EP News Wire Reports|title=New U.S. pollinator strategy emphasizes science, industry collaboration |url=http://epnewswire.com/stories/510545740-new-u-s-pollinator-strategy-emphasizes-science-industry-collaboration |work=EPNewswire |date=May 19, 2015|access-date=January 5, 2024|archive-url=https://web.archive.org/web/20150930154848/http://epnewswire.com/stories/510545740-new-u-s-pollinator-strategy-emphasizes-science-industry-collaboration|archive-date=September 30, 2015|url-status=live}}</ref>}}

Many of the priority projects that the National Strategy identified focused on the [[Interstate 35|I-35]] corridor, which extends for {{convert|1,500|mi|km}} from Texas to Minnesota. The area through which that highway travels provides spring and summer breeding habitats in the United States' key monarch migration corridor.<ref name=strategy/><ref name=Newswire/>

The Task Force simultaneously issued a "Pollinator Research Action Plan". The Plan outlined five main action areas, covered in ten subject-specific chapters. The action areas were: (1) Setting a Baseline; (2) Assessing Environmental Stressors; (3) Restoring Habitat; (4) Understanding and Supporting Stakeholders; (5) Curating and Sharing Knowledge.<ref name=Newswire/><ref>{{cite web|author=Pollinator Health Task Force|url=https://obamawhitehouse.archives.gov/sites/default/files/microsites/ostp/Pollinator%20Research%20Action%20Plan%202015.pdf|title=Pollinator Research Action Plan|location=Washington, D.C.|pages=1–3|publisher=[[The White House]]|date=May 19, 2015|access-date=January 5, 2024}}</ref>

In May 2015, the [[United States Department of Agriculture|U.S. Department of Agriculture]] (USDA) and the [[United States Department of the Interior|U.S. Department of the Interior]] (USDI) issued a 52-page document entitled "Pollinator-Friendly Best Management Practices for Federal Lands". The document consolidated general information about the practices and procedures to use when considering pollinator needs in project development and management of Federal lands that are managed for native diversity and multiple uses. The document also contained a series of actions to be considered when determining those lands best suited for restoration and rehabilitation of monarch habitat. These included an assurance that native wildflowers are available, diverse, and abundant to provide nectar for monarchs and an assurance that milkweed species that female monarchs prefer for egg laying are available or will be planted. The document identified those milkweed species for each of seven regions within the United States.<ref>{{cite web|url=https://www.fs.usda.gov/wildflowers/pollinators/BMPs/documents/PollinatorFriendlyBMPsFederalLands05152015.pdf|title=Pollinator-Friendly Best Management Practices for Federal Lands|date=May 11, 2015|pages=7 and 35|publisher=[[United States Department of Agriculture|U.S. Department of Agriculture]] and [[United States Department of the Interior|U.S. Department of the Interior]]|access-date=March 8, 2024|archive-url=https://web.archive.org/web/20230602155443/https://www.fs.usda.gov/wildflowers/pollinators/BMPs/documents/PollinatorFriendlyBMPsFederalLands05152015.pdf|archive-date=June 2, 2023|url-status=live|quote=(p. 35) Implementation: To determine those lands best suited for restoration and rehabilitation of monarch habitat, the following actions should be considered: • Ensure that native wildflowers are available, diverse, and abundant to provide nectar for monarchs. • Ensure that milkweed species (preferred by female monarchs for egg laying) are available; if not, implement a planting program for milkweeds: o In the Eastern United States, plant swamp milkweed, butterfly milkweed, and common milkweed. o In the Southern United States, plant butterfly milkweed, swamp milkweed, aquatic milkweed, white milkweed, pinewoods milkweed, and swamp milkweed. o In the Northern Great Plains, plant showy milkweed, common milkweed, plains milkweed, green comet milkweed, and whorled milkweed. o In the Southern Great Plains, plant showy milkweed, butterfly milkweed, whorled milkweed, swamp milkweed, spider milkweed, and green antelopehorn milkweed. o For the California population, plant California milkweed, heartleaf milkweed, woollypod milkweed, Mexican whorled milkweed, also known as narrowleaf milkweed and woolly milkweed. o For the intermountain west and desert southwest plant butterfly milkweed, cor kernel milkweed, spider milkweed and pine needle milkweed. o In the Pacific Northwest, consider using showy milkweed or narrowleaf milkweed.}}{{PD-notice}}</ref>

On December 4, 2015, President Obama signed into law the [[Fixing America's Surface Transportation Act|Fixing America's Surface Transportation (FAST) Act]] (Pub. L. 114-94).<ref>{{cite web|url=https://www.govinfo.gov/content/pkg/PLAW-114publ94/pdf/PLAW-114publ94.pdf|title=Public Law 114–94: 114th Congress (129 Stat. 1312–1801)|publisher=[[United States Government Publishing Office]]|access-date=July 7, 2021|archive-url=https://web.archive.org/web/20210625115613/https://www.govinfo.gov/content/pkg/PLAW-114publ94/pdf/PLAW-114publ94.pdf|archive-date=June 25, 2021|url-status=live}}</ref> The FAST Act placed a new emphasis on efforts to support pollinators. To accomplish this, the FAST Act amended [[Title 23 of the United States Code|Title 23]] (Highways) of the [[United States Code]]. The amendment directed the [[United States Secretary of Transportation]] when carrying out programs under that title in conjunction with willing states, to:

# encourage integrated vegetation management practices on roadsides and other transportation rights-of-way, including reduced mowing; and
# encourage the development of habitat and forage for Monarch butterflies, other native pollinators, and honey bees through plantings of native [[forb]]s and grasses, including noninvasive, native milkweed species that can serve as migratory way stations for butterflies and facilitate migrations of other pollinators.<ref name=Code>Multiple sources:
* {{cite web|url=https://www.govinfo.gov/content/pkg/PLAW-114publ94/pdf/PLAW-114publ94.pdf|title=Sec. 1415. Administrative Provisions To Encourage Pollinator Habitat And Forage On Transportation Rights-Of-Way|work=Public Law 114–94: 114th Congress (129 Stat. 1421)|publisher=[[United States Government Publishing Office]]|access-date=July 7, 2021|archive-url=https://web.archive.org/web/20210625115613/https://www.govinfo.gov/content/pkg/PLAW-114publ94/pdf/PLAW-114publ94.pdf|archive-date=June 25, 2021|url-status=live}}
* {{cite web|url=https://www.law.cornell.edu/uscode/text/23/319|title=23 U.S. Code § 319 - Landscaping and scenic enhancement|location=[[Ithaca, New York]]|publisher=[[Cornell Law School]]: [[Legal Information Institute]]|access-date=July 7, 2021|archive-url=https://web.archive.org/web/20210301035558/https://www.law.cornell.edu/uscode/text/23/319|archive-date=March 1, 2021|url-status=live|quote='''(c) Encouragement of Pollinator Habitat and Forage Development and Protection on Transportation Rights-of-way.—'''In carrying out any program administered by Secretary under this title, the Secretary shall, in conjunction with willing States, as appropriate – '''(1)''' encourage integrated vegetation management practices on roadsides and other transportation rights-of-way, including reduced mowing; and '''(2)''' encourage the development of habitat and forage for Monarch butterflies, other native pollinators, and honey bees through plantings of native forbs and grasses, including noninvasive, native milkweed species that can serve as migratory way stations for butterflies and facilitate migrations of other pollinators.}}
* {{cite web|last=Nadeau|first=Gregory G.|author-link=Gregory G. Nadeau|url=https://www.environment.fhwa.dot.gov/env_topics/ecosystems/pollinators_improving_habitat.aspx|title=Memorandum: Improving Habitat for Pollinators|date=March 25, 2016|location=Washington, D.C.|publisher=[[United States Department of Transportation]]: [[Federal Highway Administration]]|access-date=July 7, 2021|archive-date=July 9, 2021|archive-url=https://web.archive.org/web/20210709185311/https://www.environment.fhwa.dot.gov/env_topics/ecosystems/pollinators_improving_habitat.aspx|url-status=dead}}{{PD-notice}}</ref>

The FAST Act also stated that activities to establish and improve pollinator habitat, forage, and migratory way stations may be eligible for Federal funding if related to transportation projects funded under Title 23.<ref name=Code/>

In February 2016, the Office of the U.S. Secretary of the Interior issued a memorandum containing an attachment entitled "Strategy for Implementing Pollinator-Friendly Landscaping Design and Maintenance at Department of the Interior Sites". The attachment described specific actions that would address the incorporation of pollinator-friendly landscaping design and maintenance into new construction and major renovations, existing sites, contracts, leases and occupancy agreements, and education/outreach programs. The memorandum containing the attachment directed the USDI's bureaus and offices (which include the Fish and Wildlife Service, the [[Bureau of Land Management]], and the [[National Park Service]]) to implement those actions to the extent that they are appropriate for and consistent with, the mission and function of the facility/site.<ref>{{cite web|url=https://www.nps.gov/dscw/upload/PollinatorFriendlyLandscaping_DOIMemo_2-9-16.pdf|title=Attachment 1 - Strategy for Implementing Pollinator-Friendly Landscaping Design and Maintenance at Department of the Interior Sites|work=Memorandum: Increasing and Improving Pollinator Habitat through Landscaping|date=February 9, 2016|location=Washington, D.C.|publisher=Office of the [[United States Secretary of the Interior|Secretary of the Interior]]|access-date=March 8, 2024|archive-url=https://web.archive.org/web/20170212023721/https://www.nps.gov/dscw/upload/PollinatorFriendlyLandscaping_DOIMemo_2-9-16.pdf|archive-date=February 12, 2017}}</ref>

In June 2016, the Pollinator Health Task Force issued a "Pollinator Partnership Action Plan". That Plan provided examples of past, ongoing, and possible future collaborations between the federal government and non-federal institutions to support pollinator health under each of the National Strategy's goals.<ref>{{cite web|author=Pollinator Health Task Force|url=https://obamawhitehouse.archives.gov/sites/whitehouse.gov/files/images/Blog/PPAP_2016.pdf|title=Pollinator Partnership Action Plan|location=Washington, D.C.|publisher=[[The White House]]|date=June 22, 2016 |access-date=January 5, 2024}}</ref>

The USDA's [[Farm Service Agency]] helps increase U.S. populations of the monarch butterfly and other pollinators through its [[Conservation Reserve Program]]'s [[Private landowner assistance program#Agricultural conversion programs|State Acres for Wildlife Enhancement (SAFE) Initiative]]. The SAFE Initiative provides an annual rental payment to farmers who agree to remove environmentally sensitive land from agricultural production and plant species that will improve environmental health and quality. Among other things, the initiative encourages landowners to establish wetlands, grasses, and trees to create habitats for species that the USFWS has designated to be threatened or endangered.<ref>Multiple sources:
* {{cite web|url=https://www.fsa.usda.gov/Assets/USDA-FSA-Public/usdafiles/FactSheets/2019/crp_safe_initiative-fact_sheet.pdf|title=Fact Sheet: The State Acres for Wildlife Enhancement (SAFE) Initiative|work=Farm Service Agency: Conservation Reserve Program|date=December 2019|publisher=[[United States Department of Agriculture]]: [[Farm Service Agency]]|access-date=October 6, 2021|archive-url=https://web.archive.org/web/20210913002601/https://www.fsa.usda.gov/Assets/USDA-FSA-Public/usdafiles/FactSheets/2019/crp_safe_initiative-fact_sheet.pdf|archive-date=September 13, 2021}}
* {{cite web|url=https://www.fsa.usda.gov/resources/programs/conservation-reserve-program|title=Conservation Reserve Program|year=2021|publisher=[[United States Department of Agriculture]]: [[Farm Service Agency]]|access-date=October 6, 2021|archive-url=https://web.archive.org/web/20210917200603/https://www.fsa.usda.gov/programs-and-services/conservation-programs/conservation-reserve-program/index|archive-date=September 17, 2021|url-status=live}}
* {{cite web|url=https://www.fws.gov/midwest/news/SAFEpartners.html|title=Pollinators and monarchs SAFE in Wisconsin|date=December 29, 2016|work=Newsroom|publisher=[[United States Department of the Interior]]: [[Fish and Wildlife Service]]|access-date=October 6, 2021|archive-url=https://web.archive.org/web/20171231113800/https://www.fws.gov/midwest/news/SAFEpartners.html|archive-date=December 31, 2017|url-status=live}}
* {{cite web|url=http://www.namonarchs.org/incentive-programs/conservation-reserve-program-crp/|title=Incentive Programs: Conservation Reserve Program (CRP): United States Department of Agriculture Farm Service Agency (FSA)|work=Monarch Conservation Toolbox|date=May 18, 2017 |location=[[Montreal]], [[Quebec]], Canada|publisher=Commission for Environmental Cooperation|access-date=October 6, 2021|archive-url=https://web.archive.org/web/20200115125341/http://www.namonarchs.org/incentive-programs/conservation-reserve-program-crp/|archive-date=January 15, 2020|url-status=live}}</ref>

As part of its targeted monarch butterfly effort, the USDA's [[Natural Resources Conservation Service]] (NRCS) works with agricultural producers in the midwest and southern [[Great Plains]] to combat the decline of monarch butterflies by planting milkweed and other nectar-rich plants on private lands. The NRCS also provides region-specific guides and plant lists that support populations of monarch butterflies and other pollinators in the Greater Appalachian Mountains Region, the Midwest Region, the Northern and Southern Great Plains, and the Western Coastal Plain.<ref>{{cite web|url=https://www.nrcs.usda.gov/programs-initiatives/monarch-butterflies|title=Monarch Butterflies|date=September 27, 2023 |publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]|access-date=February 2, 2024|archive-url=https://web.archive.org/web/20231217155336/https://www.nrcs.usda.gov/programs-initiatives/monarch-butterflies|archive-date=December 17, 2023|url-status=live}}</ref>

In January 2024, staff of the [[National Capital Planning Commission]] (the federal government's planning agency for the [[Washington metropolitan area|National Capital Region]]) introduced a "Pollinator Best Practices Resource Guide". The Guide summarizes existing federal guidance from the [[Council on Environmental Quality]], the USDA, and the GSA regarding best practices for creating pollinator habitats in both meadow and non-meadow/designed landscapes. When discussing milkweeds, the Guide states that although more than 100 species of such plants are considered native to North America, ''Asclepias syriaca'', or common milkweed, stands out and "is clearly an important species that is critical to the survival of monarch butterflies".<ref>{{cite web|first=Stephanie|last=Free|date=January 4, 2024|title=Information Presentation: Pollinator Best Practices Resource Guide|id=NCPC File Number 8510|location=Washington, D.C.|publisher=[[National Capital Planning Commission]]|url=https://www.ncpc.gov/docs/actions/2024January/8510_Pollinator_Best_Practices_Resource_Guide_Information_Sheet_Jan2024.pdf|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250204063216/https://www.ncpc.gov/docs/actions/2024January/8510_Pollinator_Best_Practices_Resource_Guide_Information_Sheet_Jan2024.pdf|archive-date=February 4, 2025|url-status=live|quote=There are over 100 different species of milkweeds that are considered native to North America7, one of which stands out - Asclepias syriaca, or common milkweed. According to the U.S. Forest Service, Common milkweed is, "...among the most important food plants for Monarch caterpillars," and, "Nature's mega food market for insects. Over 450 insects are known to feed on some portion of the plant. Numerous insects are attracted to the nectar-laden flowers and it is not at all uncommon to see flies, beetles, ants, bees, wasps, and butterflies on the flowers at the same time." The Xerces Society has also identified Common milkweed as a priority species for habitat restoration efforts.8 Common milkweed also quickly spreads through rhizomatous roots and forms colonies which aids in its longevity. Therefore, common milkweed is clearly an important species that is critical to the survival of monarch butterflies.}}</ref>

===Other actions===
Agriculture companies and other organizations are being asked to set aside unsprayed areas to allow monarchs to breed. In addition, national and local initiatives are underway to help establish and maintain pollinator habitats along corridors containing power lines and roadways. The [[Federal Highway Administration]], state governments, and local jurisdictions are encouraging highway departments and others to limit their use of herbicides, to reduce mowing, to help milkweed to grow, and to encourage monarchs to reproduce within their right-of-ways.<ref name="Brennen"/><ref name=Tennessee>Multiple sources:
* {{cite book|last1=Hopwood|first1=Jennifer|last2=Black|first2=Scott|last3=Fleury|first3=Scott|url=https://www.environment.fhwa.dot.gov/env_topics/ecosystems/Pollinators_Roadsides/BMPs_pollinators_roadsides.pdf|title=Pollinators and Roadsides: Best Management Practices for Managers and Decision Makers|date=December 2015|oclc=1252634388|location=Washington, D.C.|publisher=[[United States Department of Transportation]]: [[Federal Highway Administration]]|id=FHWA-HEP-16-020|access-date=July 9, 2021|archive-url=https://web.archive.org/web/20210602010726/https://www.environment.fhwa.dot.gov/env_topics/ecosystems/Pollinators_Roadsides/BMPs_pollinators_roadsides.pdf|archive-date=June 2, 2021|url-status=live}}
* {{cite book|first1=Jennifer|last1=Hopwood|first2=Scott|last2=Black|first3=Scott|last3=Fleury|date=December 2015|url=https://www.environment.fhwa.dot.gov/env_topics/ecosystems/Pollinators_Roadsides/BMPs_pollinators_landscapes_hi-rez.pdf|title=Roadside Best Management Practices that Benefit Pollinators: Handbook for Supporting Pollinators through Roadside Maintenance and Landscape Design|oclc=1252634401|location=Washington, D.C.|publisher=[[United States Department of Transportation]]: [[Federal Highway Administration]]|id=FHWA-HEP-16-059|archive-url=https://web.archive.org/web/20210601210318/https://www.environment.fhwa.dot.gov/env_topics/ecosystems/Pollinators_Roadsides/BMPs_pollinators_landscapes_hi-rez.pdf|archive-date=June 1, 2021|url-status=live}}
* {{cite journal|first1=Deirdre|last1=Remley|first2=Allison|last2=Redmon|date=September 2017|url=https://highways.dot.gov/public-roads/september-2017/save-bees-and-butterflies|title=Save The Bees and Butterflies!|journal=Public Roads|volume=81|number=2|location=Washington, D.C.|publisher=[[United States Department of Transportation]]: [[Federal Highway Administration]]|id=FHWA-HRT-17-006|archive-url=https://web.archive.org/web/20201112003434/https://www.fhwa.dot.gov/publications/publicroads/17sept/01.cfm|archive-date=November 12, 2020}}
* {{cite news|first= Margaret|last=Renkl|date=September 16, 2019|title=Tennessee Makes Way for Monarchs|url=https://www.nytimes.com/2019/09/16/opinion/tennessee-wildflowers-nature.html|newspaper=[[The New York Times]]|access-date=July 7, 2021|archive-url=https://web.archive.org/web/20201125033333/https://www.nytimes.com/2019/09/16/opinion/tennessee-wildflowers-nature.html|archive-date=November 25, 2020}}</ref>

====State and local governments====

A Scientific Collecting Permit (SCP) is required to handle wild monarchs in California including for educational purposes. It is unlawful to collect, remove from the wild and/or captively rear monarchs in that state without an SCP.<ref>Multiple sources:
* {{cite web|title=Do I Need A Permit To Use Monarch Butterflies For Educational Purposes?|date=April 6, 2023|url=https://wildlife.ca.gov/COQA/do-i-need-a-permit-to-use-monarch-butterflies-for-educational-purposes|publisher=[[California Department of Fish and Wildlife]]|quote=Q: Do I need a permit to use monarch butterflies for educational purposes? A: Yes, a Scientific Collecting Permit (SCP) is required to handle wild monarchs in California including for educational purposes. It is unlawful to collect, remove from the wild and/or captively rear monarchs in California without an SCP, per California Code of Regulations (CCR), Title 14, section 650(a)|access-date=September 20, 2025|archive-url=https://web.archive.org/web/20250523155549/https://wildlife.ca.gov/COQA/do-i-need-a-permit-to-use-monarch-butterflies-for-educational-purposes|archive-date=May 23, 2025|url-status=live}}
* {{cite web|title=§ 650. Scientific Collecting Permits: Permits to Take or Possess Wildlife for Scientific, Educational, and/or Propagation Purposes. (a) General Provisions.|work=Scientific Collecting Laws and Regulations|url=https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=161295&inline|publisher=[[California Department of Fish and Wildlife]]|access-date=September 20, 2025|archive-url=https://web.archive.org/web/20250618112350/https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=161295&inline|archive-date=June 18, 2025|url-status=live|quote=(a) General Provisions. Except as otherwise authorized by the Fish and Game Code or regulations adopted pursuant thereto, it shall be unlawful for any person or entity to take and/or possess live or dead wildlife, or parts thereof in any part of the State of California, for scientific, educational, and/or propagation purposes except as authorized by a permit issued by the department pursuant to this Section.}}</ref> 

As of June 2025, at least 14 states (California, Connecticut, Illinois, Kentucky, Maryland, Massachusetts, Minnesota, Missouri, New Jersey, New Mexico, New York, North Carolina, Ohio, Vermont and Washington) had enacted legislation to protect, develop and restore habitat suitable for pollinators.<ref>Multiple sources:
* {{cite web|author=National Conference of State Legislatures|author-link=National Conference of State Legislatures|date=April 19, 2023|title=Pollinator Health|url=https://www.ncsl.org/environment-and-natural-resources/pollinator-health|location=Denver, Colorado, and Washington, D.C.|archive-url=https://web.archive.org/web/20250605063222/https://www.ncsl.org/environment-and-natural-resources/pollinator-health|archive-date=June 5, 2025|url-status=live|access-date=August 31, 2025}}
* {{cite web|last1=Blackledge|first1=Steve|last2=Kelly-Fischer|first2=Patrick|last3=Cummings|first3=Deirdre|date=June 16, 2025|title=A snapshot of state actions to protect pollinators: By limiting bee-killing neonics, conserving habitat and raising awareness, states are key actors in the campaign to protect pollinators|url=https://environmentamerica.org/resources/a-snapshot-of-state-actions-to-protect-pollinators/|publisher=[[Environment America]]|location=Denver, Colorado|url-status=live|archive-url=https://web.archive.org/web/20250625174837/https://environmentamerica.org/resources/a-snapshot-of-state-actions-to-protect-pollinators/|archive-date=June 25, 2025|access-date=August 31, 2025}}</ref> For example, the [[New Jersey General Assembly]] considered legislation in 2014 that was intended to increase the monarch butterfly's migrating population within the state.<ref>{{cite web|first=Dale|last=Gerhard|title=Dwindling monarch butterflies in Cape May County has legislators worried|date=September 14, 2014|url=http://www.pressofatlanticcity.com/communities/upper_capemay/dwindling-monarch-butterflies-in-cape-may-county-has-legislators-worried/article_09d41cec-3c74-11e4-b3bc-439ee8bb143f.html|work=[[The Press of Atlantic City]]|location=[[Linwood, New Jersey]]|archive-url=https://web.archive.org/web/20180526041040/http://www.pressofatlanticcity.com/communities/upper_capemay/dwindling-monarch-butterflies-in-cape-may-county-has-legislators-worried/article_09d41cec-3c74-11e4-b3bc-439ee8bb143f.html|archive-date=May 26, 2018}}</ref> [[Government of New Jersey|New Jersey's government]] subsequently approved legislation in May 2017 that established an "Integrated Roadside Vegetation Management Program". Among other things, the legislation required the [[New Jersey Department of Transportation|state's transportation department]] to develop and adopt a plan for "cost effective maintenance and planting along roadsides, with an emphasis on adaptable vegetation with long life cycles, native vegetation, and wildflowers".<ref>{{cite web|title=Integrated Roadside Vegetation Management Program|id=P.L.2017, Chapter 44|url=https://pub.njleg.gov/Bills/2016/AL17/44_.HTM|date=May 1, 2017|publisher=[[New Jersey Legislature]]|access-date=August 9, 2025|archive-url=https://web.archive.org/web/20241201204707/https://pub.njleg.gov/Bills/2016/AL17/44_.HTM|archive-date=December 1, 2024|url-status=live}}</ref> 

In January 2018, the New Jersey government approved an "Adopt a Monarch Butterfly Waystation Act" and a "Milkweed for Monarchs Act". The latter act required the [[New Jersey Department of Environmental Protection|state's environmental protection department]] to establish criteria for the planting of milkweed in stormwater management basins on state-owned lands and to take related actions.<ref>Multiple sources:
* {{cite web|title=Adopt a Monarch Butterfly Waystation Act|id=P.L.2017, Chapter 250|url=https://pub.njleg.gov/bills/2016/AL17/250_.HTM|date=January 8, 2018|publisher=[[New Jersey Legislature]]|access-date=July 30, 2025|archive-url=https://web.archive.org/web/20250730090720/https://pub.njleg.gov/bills/2016/AL17/250_.HTM|archive-date=July 30, 2025|url-status=live}}
* {{cite web|title=Milkweed for Monarchs Act|id=P.L.2017, Chapter 252|url=https://pub.njleg.gov/bills/2016/AL17/252_.HTM|date=January 8, 2018|publisher=[[New Jersey Legislature]]|access-date=July 30, 2025|archive-url=https://web.archive.org/web/20250730092333/https://pub.njleg.gov/bills/2016/AL17/252_.HTM|archive-date=July 30, 2025|url-status=live}}</ref>

In June 2019, [[Tennessee Department of Transportation|Tennessee's transportation department]] announced a partnership with the state's [[Tennessee Department of Environment and Conservation|environment and conservation]] and [[Tennessee Department of Agriculture|agriculture]] departments to promote pollinator health and awareness in the state's parks. The partners expected to install pollinator meadows and interpretive signage in nine such parks.<ref>{{cite web|title=Three Departments Partner on Pollinator Initiative in Tennessee State Parks: TDOT, TDEC, TDA benefit pollinators, spread awareness|date=June 18, 2019|url=https://www.tn.gov/tdot/news/2019/6/18/three-departments-partner-on-pollinator-initiative-in-tennessee-state-parks.html|location=Nashville, Tennessee|publisher=[[Tennessee Department of Transportation]]|archive-url=https://web.archive.org/web/20250125001656/https://www.tn.gov/tdot/news/2019/6/18/three-departments-partner-on-pollinator-initiative-in-tennessee-state-parks.html|archive-date=January 25, 2025}}</ref> [[Virginia Department of Wildlife Resources|Virginia's wildlife resources department]] encourages plantings of native species that are highly beneficial to pollinators, such as ''[[Asclepias]]'' (milkweeds), ''[[Pycnanthemum]]'' (mountain mints), and plants in the [[Asteraceae]] family, which includes ''[[Coreopsis]]'', ''[[Helianthus]]'' (sunflowers), ''[[Rudbeckia]]'' (coneflowers), ''[[Solidago]]'' (goldenrods),  and ''[[Eutrochium]]'' (Joe-Pye weeds).<ref>Multiple sources:
* {{cite web|first=Carol A.|last=Heiser|title=Celebrate Pollinators!|date=June 24, 2020|url=https://dwr.virginia.gov/blog/celebrate-pollinators/|publisher=[[Virginia Department of Wildlife Resources]]|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250625124359/https://dwr.virginia.gov/blog/celebrate-pollinators/|archive-date=June 25, 2025|url-status=live}}
* {{cite web|first=Bruce|last=Ingram|date=June 9, 2022|title=Help the Bees, Butterflies, Bucks, and Bears: Create a Pollinator Plot|url=https://dwr.virginia.gov/blog/help-the-bees-butterflies-bucks-and-bears-create-a-pollinator-plot/|publisher=[[Virginia Department of Wildlife Resources]]|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250627205902/https://dwr.virginia.gov/blog/help-the-bees-butterflies-bucks-and-bears-create-a-pollinator-plot/|archive-date=June 27, 2025|url-status=live}}
</ref>

In April 2025, the [[Chicago Park District]]'s general superintendent launched "Project Monarch", a citywide initiative to conserve and celebrate monarch butterflies and their habitats.<ref>{{cite web|title=Project Monarch|url=https://www.chicagoparkdistrict.com/project-monarch|year=2025|location=Chicago, Illinois|publisher=[[Chicago Park District]]|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250517080211/https://www.chicagoparkdistrict.com/project-monarch|archive-date=May 17, 2025|url-status=live}}</ref> In addition, many local jurisdictions throughout the United States have made commitments to increase monarch habitat by joining "Monarch City USA" or by taking the [[National Wildlife Federation]]'s "Mayors' Monarch Pledge" and planting native milkweeds and other nectar plants within their boundaries.<ref>Multiple sources:
* {{cite web|title=Monarch City USA Members|url=http://www.monarchcityusa.com/members|publisher=Monarch City USA|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250619040738/http://www.monarchcityusa.com/members|archive-date=June 19, 2025|url-status=live}}
* {{cite web|title=Monarch Butterfly Recovery: City by City|year=2014|url=http://www.monarchcityusa.com|publisher=Monarch City USA|access-date=July 29, 2025|archive-url=https://web.archive.org/web/20250619044632/https://www.monarchcityusa.com/|archive-date=June 19, 2025|url-status=live}}
* {{cite web|title=Ways to help|url=http://www.monarchcityusa.com/get-involved|publisher=Monarch City USA|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250813072528/https://www.monarchcityusa.com/get-involved|archive-date=August 13, 2025|url-status=live}}
* {{cite web|title=Orange City recently named a Monarch City USA|date=25 July 2019|location=[[South Daytona, Florida]]|publisher=Hometown News Volusia|url=https://www.hometownnewsvolusia.com/news/orange-city-recently-named-a-monarch-city-usa/article_81f020d2-ae2e-11e9-b2dc-579a8468aadd.htm|access-date=July 30, 2025|archive-url=https://web.archive.org/web/20250730060529/https://www.hometownnewsvolusia.com/news/orange-city-recently-named-a-monarch-city-usa/article_81f020d2-ae2e-11e9-b2dc-579a8468aadd.htm|archive-date=July 30, 2025|url-status=live}} 
* {{cite web|title=Monarch City|url=https://www.clemsoncity.org/452/Monarch-City|publisher=Government of the [[Clemson, South Carolina|City of Clemson, South Carolina]]|access-date=July 30, 2025|archive-url=https://web.archive.org/web/20250329192400/https://www.clemsoncity.org/452/Monarch-City|archive-date=March 29, 2025|url-status=live}}
* {{cite web|title=Mayors' Monarch Pledge|url=https://www.nwf.org/MayorsMonarchPledge|location=[[Merrifield, Virginia]]|publisher=[[National Wildlife Federation]]|access-date=July 29, 2025|archive-url=https://web.archive.org/web/20250629212626/https://www.nwf.org/mayorsmonarchpledge|archive-date=June 29, 2025|url-status=live}}
* {{cite web|title=Signatories - Mayors' Monarch Pledge|work=Mayors' Monarch Pledge|year=2025|url=https://mayorsmonarchportal.nwf.org/Signatories|location=[[Merrifield, Virginia]]|publisher=[[National Wildlife Federation]]|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250813085332/https://mayorsmonarchportal.nwf.org/Signatories|archive-date=August 13, 2025|url-status=live}}
* {{cite web|title=Mayors' Monarch Pledge Action Items|work=Mayors' Monarch Pledge|url=https://www.nwf.org/~/media/PDFs/Garden-for-Wildlife/Mayors-Monarch-Pledge_Action-Items.pdf|location=[[Merrifield, Virginia]]|publisher=[[National Wildlife Federation]]|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20240224114518/https://www.nwf.org/~/media/PDFs/Garden-for-Wildlife/Mayors-Monarch-Pledge_Action-Items.pdf|archive-date=February 24, 2024|url-status=live}}
* {{cite web|last=Garvey|first=Libby|title=Monarch Pledge Day|url=https://www.arlingtonva.us/Government/Departments/County-Board/Board-Actions/Proclamations/Monarch-Pledge-Day-2016|date=June 21, 2016|publisher=Government of [[Arlington County, Virginia]]|access-date=July 29, 2025|archive-url=https://web.archive.org/web/20241008114516/https://www.arlingtonva.us/Government/Departments/County-Board/Board-Actions/Proclamations/Monarch-Pledge-Day-2016|archive-date=October 8, 2024|url-status=live}}
* {{cite web|first=Ashley|last=Adams|date=August 3, 2023|title=Pennsylvania's Conservation Heroes: 14 Municipalities Unite to Save the Monarch Butterfly: Municipalities across the commonwealth have pledged to create habitats and educate their communities to help save the monarch butterfly, which contributes to the health of the planet as a pollinator.|url=https://keystonenewsroom.com/2023/08/03/pennsylvanias-conservation-heroes-14-municipalities-unite-to-save-the-monarch-butterfly/|work=The Keystone|publisher=[[Courier Newsroom]]|access-date=August 13, 2025|archive-url=https://web.archive.org/web/20250607214318/https://keystonenewsroom.com/2023/08/03/pennsylvanias-conservation-heroes-14-municipalities-unite-to-save-the-monarch-butterfly/|archive-date=June 7, 2025|url-status=live}}
* {{cite web|title=Mesa Mayor Mark Freeman Signs National Wildlife Federation's Monarch Pledge|date=March 19, 2025|work=MesaNow.org|url=https://www.mesanow.org/news/gpublic/article/3458|publisher=Government of the [[Mesa, Arizona|City of Mesa, Arizona]]|access-date=July 30, 2025|archive-url=https://web.archive.org/web/20250519055246/https://www.mesanow.org/news/public/article/3458|archive-date=May 19, 2025|url-status=live}}</ref> Many cities, towns, counties, and communities have joined “[[Xerces Society#Bee City USA|Bee City USA]]” (an initiative of the [[Xerces Society|Xerces Society for Invertebrate Conservation]]) and made commitments to conserve native bees, butterflies and other pollinators by increasing the abundance of native plants, providing nesting sites, and reducing the use of pesticides.<ref>Multiple sources:
* {{cite web|title=Bee City USA|url=https://beecityusa.org/|location=[[Portland, Oregon]]|publisher=[[Xerces Society|Xerces Society for Invertebrate Conservation]]|access-date=November 15, 2025|archive-url= https://web.archive.org/web/20251002233701/https://beecityusa.org/|archive-date=October 2, 2025|url-status=live}}
* {{cite web|title=About Bee City USA & Bee Campus USA|work=Bee City USA|url=https://beecityusa.org/about|location=[[Portland, Oregon]]|publisher=[[Xerces Society|Xerces Society for Invertebrate Conservation]]|access-date=November 15, 2025|archive-url= https://web.archive.org/web/20250921142027/https://beecityusa.org/about/|archive-date=September 21, 2025|url-status=live|quote=In 2018 Bee City USA and Bee Campus USA became initiatives of the [[Xerces Society|Xerces Society for Invertebrate Conservation]] .... The steps that affiliates take to conserve our native bees, including creating safe habitats and hosting community events, will also help other pollinators including butterflies and moths as well as the non-native honey bee.}}
* {{cite web|title=Bee City USA commitments|work=Bee City USA|url=https://beecityusa.org/bee-city-usa-commitments/|location=[[Portland, Oregon]]|publisher=[[Xerces Society|Xerces Society for Invertebrate Conservation]]|access-date=September 6, 2024|archive-url=https://web.archive.org/web/20250921142027/https://beecityusa.org/bee-city-usa-commitments/|archive-date=September 21, 2025|url-status=live}}
* {{cite web|title=Bee City USA affiliates|work=Bee City USA|url=https://beecityusa.org/current-bee-city-usa-affiliates/|location=[[Portland, Oregon]]|publisher=[[Xerces Society|Xerces Society for Invertebrate Conservation]]|access-date=November 15, 2025|archive-url= https://web.archive.org/web/20250921142027/https://beecityusa.org/current-bee-city-usa-affiliates/|archive-date=September 21, 2025|url-status=live}}
* {{cite web|title=Bee City USA|work=City of Bellingham |url=https://cob.org/services/environment/bee-city-usa|publisher=[[Bellingham, Washington#Government|City of Bellingham, Washington, government]]|access-date=November 16, 2025|archive-url=https://web.archive.org/web/20250531213136/https://cob.org/services/environment/bee-city-usa|archive-date=May 31, 2025|url-status=live}}
* {{cite web|title=Fauquier County-Bee City USA|url=https://www.fauquiercounty.gov/government/departments-h-z/parks-and-recreation/bee-city-usa|publisher=[[Fauquier County, Virginia#Government|Fauquier County, Virginia, government]]|access-date=November 16, 2025|archive-url= https://web.archive.org/web/20250907120226/http://www.fauquiercounty.gov/government/departments-h-z/parks-and-recreation/bee-city-usa|archive-date=September 7, 2025|url-status=live}}
* {{cite web|title=Bee City USA|url=https://www.matthewsnc.gov/pview.aspx?id=20875&catid=0|publisher=[[Matthews, North Carolina|Town of Matthews, North Carolina, government]]|access-date=November 16, 2025|archive-url= https://web.archive.org/web/20240629131433/https://www.matthewsnc.gov/pview.aspx?id=20875&catid=0|archive-date=June 29, 2024|url-status=live}}</ref>

====National Cooperative Highway Research Program report====
In 2020, the [[National Cooperative Highway Research Program]] (NCHRP) of the [[Transportation Research Board]] issued a 208-page report that described a project that had examined the potential for roadway corridors to provide habitat for monarch butterflies. A part of the project developed tools for roadside managers to optimize potential habitats for monarch butterflies in their road rights-of-way.<ref>Multiple sources:
* {{cite book |url=http://www.trb.org/Publications/Blurbs/180186.aspx|title=Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies|year=2020|lccn=2020935714|isbn=978-0-309-48132-8|oclc=1229163481|doi=10.17226/25693|location=Washington, D.C.|publisher=[[National Academies Press]]|s2cid=218854539|id=[[National Cooperative Highway Research Program|National Cooperative Highway Research Program (NCHRP)]] Research Report 942|access-date=July 8, 2021|archive-url=https://web.archive.org/web/20200729123529/http://www.trb.org/Publications/Blurbs/180186.aspx|archive-date=July 29, 2020|url-status=live|last1=Cariveau |first1=Alison B. |last2=Caldwell |first2=Wendy |last3=Lonsdorf |first3=Eric |last4=Nootenboom |first4=Chris |last5=Tuerk |first5=Karen |last6=Snell-Rood |first6=Emilie |last7=Anderson |first7=Eric |last8=Baum |first8=Kristen A. |last9=Hopwood |first9=Jennifer |last10=Oberhauser |first10=Karen |bibcode=2020nap..book25693N }}
* {{cite web|first1=A.B.|last1=Cariveau|first2=W.|last2=Caldwell|first3=E.|last3=Lonsdorf|first4=C.|last4=Nootenboom|first5=K.|last5=Tuerk|first6=E.|last6=Snell-Rood|first7=E.|last7=Anderson|first8=K. A.|last8=Baum|first9=J.|last9=Hopwood|first10=K.|last10=Oberhauser|year=2019|url=https://files.library.northwestern.edu/transportation/online/unrestricted/repository/2020/25693.pdf|title=Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies|oclc=1152199695|location=Washington, D.C.|publisher=[[Transportation Research Board]]|id=Pre-publication draft of NCHRP Research Report 942|access-date=July 8, 2021|via=[[Northwestern University Library]]|archive-url=https://web.archive.org/web/20210708191304/https://files.library.northwestern.edu/transportation/online/unrestricted/repository/2020/25693.pdf|archive-date=July 8, 2021|url-status=live}}</ref>

Such efforts are controversial because the risk of butterfly mortality near roads is high. Several studies have shown that motor vehicles kill millions of monarchs and other butterflies annually.<ref name="monarchscience"/> Also, some evidence indicates that monarch larvae living near roads experience physiological stress conditions, as evidenced by elevations in their heart rate.<ref>{{Cite journal|last1=Davis|first1=Andrew K.|last2=Schroeder|first2=Hayley|last3=Yeager|first3=Ian|last4=Pearce|first4=Jana|date=May 31, 2018 |title=Effects of simulated highway noise on heart rates of larval monarch butterflies, ''Danaus plexippus'': implications for roadside habitat suitability|journal=[[Biology Letters]] |volume=14 |issue=5 |article-number=20180018 |doi=10.1098/rsbl.2018.0018 |pmc=6012697 |pmid=29743264}}</ref>

The NCHRP report acknowledged that, among other hazards, roads present a danger of traffic collisions for monarchs, stating that these effects appear to be more concentrated in particular funnel areas during migration.<ref name=NCHRP3>{{cite web |first1=A. B. |last1=Cariveau |first2=W.|last2=Caldwell|first3=E.|last3=Lonsdorf|first4=C.|last4=Nootenboom|first5=K.|last5=Tuerk|first6=E.|last6=Snell-Rood|first7=E.|last7=Anderson|first8=K. A.|last8=Baum|first9=J.|last9=Hopwood|first10=K.|last10=Oberhauser|year=2019|url=https://files.library.northwestern.edu/transportation/online/unrestricted/repository/2020/25693.pdf|title=Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies|pages=2–3|oclc=1152199695|location=Washington, D.C.|publisher=[[Transportation Research Board]]|id=Pre-publication draft of NCHRP Research Report 942|access-date=July 8, 2021|via=[[Northwestern University Library]]|archive-url=https://web.archive.org/web/20210708191304/https://files.library.northwestern.edu/transportation/online/unrestricted/repository/2020/25693.pdf|archive-date=July 8, 2021|url-status=live}}</ref> Nevertheless, the report concluded:

{{blockquote|In summary, threats along roadway corridors exist for monarchs and other pollinators, but in the context of the amount of habitat needed for recovery of sustainable populations, roadsides are of vital importance.<ref name=NCHRP3/>}}

===Butterfly gardening and monarch waystations===
{{further|Butterfly gardening}}
[[File:Monarch Butterfly waystation sign.jpg|thumb|A monarch waystation near the town of [[Berwyn Heights, Maryland|Berwyn Heights]] in [[Prince George's County, Maryland]] (June 2017)]]
The practice of butterfly gardening and creating "monarch waystations" is commonly thought to increase the populations of butterflies.<ref>Multiple sources:
* {{cite book|last=Glassberg|first=J.|year=1995|url=https://books.google.com/books?id=gwhxPwAACAAJ|title=Enjoying Butterflies More: Attract Butterflies to Your Backyard|location=[[Marietta, Ohio]]|publisher=Bird Watcher's Digest Press|isbn=1-880241-08-0|lccn=96202681|oclc=35808599|access-date=March 9, 2020|via=[[Google Books]]}}
* {{cite web|archive-url=https://web.archive.org/web/20200202135410/https://monarchwatch.org/garden/|archive-date=February 2, 2020|url-status=live|url=https://monarchwatch.org/garden/|title=Butterfly Gardening: Introduction|location=[[University of Kansas]]|publisher=[[Monarch Watch]]|access-date=March 9, 2020}}
* {{cite web|archive-url=https://web.archive.org/web/20200309145328/https://www.pollinator.org/pollinator.org/assets/generalFiles/MonarchGardenPlants.pdf|archive-date=March 9, 2020|url=https://www.pollinator.org/pollinator.org/assets/generalFiles/MonarchGardenPlants.pdf| title=Monarch Garden Plants|location=[[San Francisco]], [[California]]|publisher=[[Pollinator Partnership]]|access-date=March 9, 2020}}
* {{cite web|url=http://www.monarchwatch.org/waystations/|archive-url=https://web.archive.org/web/20170602220343/http://monarchwatch.org/waystations/|archive-date=June 2, 2017|url-status=live|access-date=June 5, 2017|title=Monarch Waystation Program|location=[[University of Kansas]]|publisher=[[Monarch Watch]]}}
* {{cite web|last=Abugattas|first=Alonzo|url=http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|title=Monarch Way Stations|date=January 3, 2017|access-date=June 5, 2017|via=[[Blogger (service)|Blogger]]|archive-url=https://web.archive.org/web/20170605221624/http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|archive-date=June 5, 2017|url-status=live}}
* {{cite web|url=https://www.monarchwatch.org/garden/plant-list-monarchwatch.pdf|title=Plants for Butterfly and Pollinator Gardens: Native and Non-native Plants Suitable for Gardens in the Northeastern United States|publisher=[[Monarch Watch]]|access-date=October 18, 2020|archive-url=https://web.archive.org/web/20200809145951/https://www.monarchwatch.org/garden/plant-list-monarchwatch.pdf|archive-date=August 9, 2020|url-status=live}}</ref> Efforts to restore falling monarch populations by establishing [[Butterfly gardening|butterfly garden]]s and monarch waystations require particular attention to the butterfly's food preferences and population cycles, as well to the conditions needed to propagate and maintain milkweed.<ref>Multiple sources:
* {{cite web|last1=Borders|first1=Brianna|last2=Lee–Mäder|first2=Eric|year=2014|url=https://www.fws.gov/southwest/es/Documents/R2ES/Pollinators/8-Milkweeds_Handbook_XerSoc_June2014.pdf|title=Milkweed Propagation and Seed Production|work=Milkweeds: A Conservation Practitioner's Guide: Plant Ecology, Seed Production Methods, and Habitat Restoration Opportunities|pages=21–95|location=[[Portland, Oregon]]|publisher=[[Xerces Society|The Xerces Society for Invertebrate Conservation]]|access-date=July 12, 2021|archive-url=https://web.archive.org/web/20210704050023/https://www.fws.gov/southwest/es/Documents/R2ES/Pollinators/8-Milkweeds_Handbook_XerSoc_June2014.pdf|archive-date=July 4, 2021|url-status=live}}
* {{cite journal|first1=Thomas D.|last1=Landis|first2=R. Kasten|last2=Dumroese|url=https://www.fs.usda.gov/rm/pubs_journals/2015/rmrs_2015_landis_t001.pdf|title=Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat: Propagating Native Milkweeds: Seed Propagation|journal=International Plant Propagators' Society, Combined Proceedings (2014)|year=2015|volume=64|page=302|access-date=July 27, 2025|archive-url=https://web.archive.org/web/20250224032937/https://www.fs.usda.gov/rm/pubs_journals/2015/rmrs_2015_landis_t001.pdf|archive-date=February 24, 2025|url-status=live|via=[[United States Department of Agriculture]]: [[United States Forest Service]]|quote=Any of the standard seed propagation methods (Landis et al., 1999) are effective with milkweed. Direct sowing of non-stratified seeds during the fall followed by exposure to ambient winter conditions can be effective, but the seeds must be mulched and protected. Cover sown seeds with a thin mulch; research has found that common milkweed seeds germinate better when planted 1 to 2 cm (0.4 to 0.8 in.) deep than when at the soil surface (Jeffery and Robison, 1971).}}</ref>

For example, in the [[Washington, D.C.]], area and elsewhere in the northeastern and midwestern United States, common milkweed (''Asclepias syriaca'') is among the most important food plants for monarch caterpillars.<ref name=Taylor1/><ref>{{cite web|last=Taylor|first=David|title=Common Milkweed (''Asclepias syriaca'' L.)|work=Plant of the Week|url=https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_syriaca.shtml|access-date=December 24, 2023|archive-url=https://web.archive.org/web/20230122001337/https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_syriaca.shtml|archive-date=January 22, 2023|url-status=live|publisher=[[United States Department of Agriculture]], [[United States Forest Service]]}}</ref> Within its range it can be found in a broad array of habitats from croplands to pastures, roadsides, ditches and old fields.<ref name=syriaca>{{cite web|url=https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-syriaca/|title=''Asclepias syriaca'', (Common Milkweed)|work=Bring Back The Monarchs|publisher=[[Monarch Watch]]|access-date=March 10, 2024|archive-url=https://web.archive.org/web/20231208065758/https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-syriaca/|archive-date=December 8, 2023|url-status=live}}</ref> The plant typically grows to a height of 3-5 feet (0.9-1.5 m), but can reach 8 feet (2.4 m) in ditches and gardens.<ref name=syriaca/> A USDA conservation planting guide for [[Maryland]] recommends that, for optimum wildlife and pollinator habitat in [[Mesic habitat|mesic]] sites, a seed mix containing 30 seeds for each square foot of planting area should have 17.0% ''A. syriaca'' by weight and 6.0% by seed.<ref>{{cite web|author=United States Department of Agriculture|date=January 2017|url=https://efotg.sc.egov.usda.gov/references/Delete/2017-1-21/MD_Cons_Planting_Guide_1_13_17_2-sided-print.pdf|title=Maryland Conservation Planting Guide|work=Mix 16: High Diversity Native Grass/Forb Mix for [[Mesic habitat|Mesic]] Sites|page=25|access-date=August 2, 2025|archive-url=https://web.archive.org/web/20250208174022/https://efotg.sc.egov.usda.gov/references/Delete/2017-1-21/MD_Cons_Planting_Guide_1_13_17_2-sided-print.pdf|archive-date=February 8, 2025|url-status=live|quote=This mix has a predominant wildflower component for optimum wildlife and pollinator habitat.}}</ref>

However, monarchs prefer to lay eggs on ''A. syriaca'' when its foliage is soft and fresh. Because monarch reproduction peaks in those areas during the late summer when milkweed foliage is old and tough, ''A. syriaca'' needs to be mowed or cut back in June through August to ensure that it will be regrowing rapidly when monarch reproduction reaches its peak. Similar conditions exist for showy milkweed (''A. speciosa'') in Michigan and for green antelope horn milkweed (''A. viridis''), where it grows in the [[Great Plains#Southern Great Plains|Southern Great Plains]] and the [[Western United States]].<ref name="Monarch Joint Venture"/><ref>Multiple sources:
*  {{cite book |url=http://www.trb.org/Publications/Blurbs/180186.aspx|title=Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies|year=2020|lccn=2020935714|isbn=978-0-309-48132-8|oclc=1229163481|doi=10.17226/25693|pages=79–80|location=Washington, D.C.|publisher=[[National Academies Press]]|s2cid=218854539|id=[[National Cooperative Highway Research Program|National Cooperative Highway Research Program (NCHRP)]] Research Report 942|access-date=July 8, 2021|archive-url=https://web.archive.org/web/20200729123529/http://www.trb.org/Publications/Blurbs/180186.aspx|archive-date=July 29, 2020|url-status=live|quote='''''Could roadside mowing stimulate milkweed growth and support monarch breeding?''''' Limited research in eastern North America has shown that spring or summer mowing can promote new growth and extend the availability of milkweed plants for monarch breeding. Mowing may stimulate the growth of some milkweed species, particularly those that spread through rhizomes like common milkweed (''A. syriaca'') and showy milkweed (''A. speciosa''). Summer (June or July) mowing in Michigan resulted in more monarch eggs on regenerated stems than on unmowed stems. Summer (July) mowing and burning can increase green antelopehorn milkweed (''A. viridis'') availability in the late summer and early fall in the Southern Great Plains, whereas in areas without mowing, the milkweed has [[Senescence|senesced]] by August. In the West, showy milkweed will regrow after summer mowing and continue to support monarch breeding (Stephanie McKnight, personal observation). However, more research is needed in other areas to determine the optimal timing and frequency of mowing that promotes not only milkweed but also nectar plants. It is also unknown if the benefit of additional milkweed availability in the fall outweighs the costs of the larval mortality caused by summer mowing. The benefits are likely greater in areas that primarily have breeding monarchs in the spring and fall and where the dominant species of milkweed spread by rhizomes. ''Sources: Alcock et al. 2016; Baum and Mueller, 2015; Bhowick 1994; Haan and Landis 2019; Fischer et al. 2015''|last1=Cariveau |first1=Alison B. |last2=Caldwell |first2=Wendy |last3=Lonsdorf |first3=Eric |last4=Nootenboom |first4=Chris |last5=Tuerk |first5=Karen |last6=Snell-Rood |first6=Emilie |last7=Anderson |first7=Eric |last8=Baum |first8=Kristen A. |last9=Hopwood |first9=Jennifer |last10=Oberhauser |first10=Karen |bibcode=2020nap..book25693N }}
* {{cite news|first=Adrian|last=Higgins|url=http://www.washingtonpost.com/lifestyle/home/creating-a-rest-stop-for-the-monarch/2015/05/26/cd81a75c-ffcb-11e4-805c-c3f407e5a9e9_story.html|title=A gardener's guide to saving the monarch|department=Home & Garden|newspaper=The Washington Post|access-date=October 17, 2020|date=May 27, 2015|archive-url=https://web.archive.org/web/20150531181342/http://www.washingtonpost.com/lifestyle/home/creating-a-rest-stop-for-the-monarch/2015/05/26/cd81a75c-ffcb-11e4-805c-c3f407e5a9e9_story.html|archive-date=May 31, 2015 |url-status=live|quote='The monarch doesn't care where the milkweed grows, and putting it in residential neighborhoods makes perfect sense,' said Doug Tallamy, an entomologist at the University of Delaware, author and expert on wildlife habitat gardens.{{nbsp}}... The [[Smithsonian Gardens#Gardens and landscapes|Smithsonian Institution's Butterfly Habitat Garden]]{{nbsp}}... and the Ripley Garden{{nbsp}}... are both good places to see milkweed integrated into a garden setting. At the butterfly garden, you can see the common milkweed{{nbsp}}... now looking pretty good in fresh, unblemished clumps. By late summer, it looks tall, tired, and tough. Tallamy says if you grow it, you should cut it back at least by half in June to produce soft foliage in late summer that will be more munchable for the caterpillars. If you do that, make sure there are no larvae on the plant before you chop it.}}
* {{cite web|last=Abugattas|first=Alonzo|url=http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|access-date=July 5, 2021|title=Monarch Way Stations|work=Capital Naturalist|date=January 3, 2017|archive-url=https://web.archive.org/web/20210308084527/http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|archive-date=March 8, 2021|url-status=live|via=[[Blogger (service)|Blogger]]|quote=Virginia is blessed for instance with 13 native ''Asclepias'' species plus 4 climbing vines that Monarch caterpillars can feed on. For the best results, cut some of the stems back in late summer after they've bloomed. Fall is when we get the most Monarchs laying eggs on our milkweeds. Since the mother butterflies prefer young, more tender growth, you can provide this by timing your pruning so there are new leaves by September or so for the arriving Monarchs. Just make sure to leave a few to produce pods for seeds. The local monarch favorite is Common Milkweed (''A. syriaca'')}}
* {{cite web|first=Tony|last=Gomez|url=https://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-syriaca/|title=''Asclepias syriaca'': Common Milkweed for Monarch Caterpillars|work=Monarch Butterfly Garden|publisher=MonarchButterflyGarden.net|access-date=October 17, 2010|archive-url=https://web.archive.org/web/20150316044421/http://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-syriaca/|archive-date=March 16, 2015|url-status=live|quote=Cut- At midseason after the blooms have faded, cut some common plants back by about a third. This promotes fresh plant growth and could get you an extra generation of monarchs on the fresh new leaves. Leave some plants uncut if you want to harvest milkweed seeds in fall.}}
* {{cite web|first=Michelle|last=Stevens|url=https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf|title=Plant guide for common milkweed (''Asclepias syriaca'')|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]: National Plant Data Center|access-date=July 5, 2021|archive-url=https://web.archive.org/web/20210705151637/https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf|archive-date=July 5, 2021|url-status=live}}</ref> Further, the seeds of ''A. syriaca'' and some other milkweeds need periods of cold treatment ([[Stratification (seeds)#Cold stratification|cold stratification]]) before they will germinate.<ref>Multiple sources:
* {{cite web|last1=Borders|first1=Brianna|last2=Lee–Mäder|first2=Eric|year=2014|url=https://www.fws.gov/southwest/es/Documents/R2ES/Pollinators/8-Milkweeds_Handbook_XerSoc_June2014.pdf|title=Milkweed Propagation and Seed Production: Stratification|work=Milkweeds: A Conservation Practitioner's Guide: Plant Ecology, Seed Production Methods, and Habitat Restoration Opportunities|pages=28–29|location=[[Portland, Oregon]]|publisher=[[Xerces Society|The Xerces Society for Invertebrate Conservation]]|access-date=July 12, 2021|archive-url=https://web.archive.org/web/20210704050023/https://www.fws.gov/southwest/es/Documents/R2ES/Pollinators/8-Milkweeds_Handbook_XerSoc_June2014.pdf|archive-date=July 4, 2021|url-status=live}}
* {{cite journal|first1=Thomas D.|last1=Landis|first2=R. Kasten|last2=Dumroese|url=https://www.fs.usda.gov/rm/pubs_journals/2015/rmrs_2015_landis_t001.pdf|title=Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat: Propagating Native Milkweeds: Seed Propagation|journal=International Plant Propagators' Society, Combined Proceedings (2014)|year=2015|volume=64|page=302|access-date=July 27, 2025|archive-url=https://web.archive.org/web/20250224032937/https://www.fs.usda.gov/rm/pubs_journals/2015/rmrs_2015_landis_t001.pdf|archive-date=February 24, 2025|url-status=live|via=[[United States Department of Agriculture]]: [[United States Forest Service]]|quote=Many sources of milkweed seeds require stratification (cold, moist treatment) before sowing. In a review of stratification requirements for common milkweed, recommendations varied from as short as 7 days to as long as 11 months at 5°C (41°F) (Luna and Dumroese, 2013). Butterfly milkweed (A. tuberosa) germination increased from 29 to 48 to 62% as stratification duration increased from 0 to 30 to 60 days, respectively (Bir, 1986). ..... Any of the standard seed propagation methods (Landis et al., 1999) are effective with milkweed. Direct sowing of non-stratified seeds during the fall followed by exposure to ambient winter conditions can be effective, but the seeds must be mulched and protected. Cover sown seeds with a thin mulch; research has found that common milkweed seeds germinate better when planted 1 to 2 cm (0.4 to 0.8 in.) deep than when at the soil surface (Jeffery and Robison, 1971).}}
* {{cite news|first=Adrian|last=Higgins|url=https://www.washingtonpost.com/lifestyle/home/a-world-of-milkweeds/2015/05/26/43fba7d6-fe6c-11e4-833c-a2de05b6b2a4_story.html|title=7 milkweed varieties and where to find them|department=Home & Garden|newspaper=The Washington Post|date=May 27, 2015|access-date=October 17, 2020|quote=Seed may be stubborn to germinate and may need a period of cold treatment.|archive-url=https://web.archive.org/web/20200926092547/https://www.washingtonpost.com/lifestyle/home/a-world-of-milkweeds/2015/05/26/43fba7d6-fe6c-11e4-833c-a2de05b6b2a4_story.html|archive-date=September 26, 2020|url-status=live}}
* {{cite web|first=Tony|last=Gomez|url=https://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-syriaca/|title=''Asclepias syriaca'': Common Milkweed for Monarch Caterpillars|work=Monarch Butterfly Garden|publisher=MonarchButterflyGarden.net|access-date=October 17, 2010|archive-url=https://web.archive.org/web/20150316044421/http://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-syriaca/|archive-date=March 16, 2015|url-status=live|quote=Start seeds indoors 2 months before final frost- seeds must be cold stratified.}}
* {{cite web|first=Michelle|last=Stevens|url=https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf|title=Plant guide for common milkweed (''Asclepias syriaca'')|publisher=[[United States Department of Agriculture]]: [[Natural Resources Conservation Service]]: National Plant Data Center|access-date=July 5, 2021|archive-url=https://web.archive.org/web/20210705151637/https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf|archive-date=July 5, 2021|url-status=live|quote=If planting in flats or in a greenhouse, common milkweed seeds should be cold-treated for three months.}}
* {{cite web|url=https://sites.google.com/site/gardeningforbutterflies/asclepias-syriaca|title=''Asclepias syriaca''|work=Butterfly gardening & all things milkweed|access-date=July 7, 2015|archive-url=https://web.archive.org/web/20150707205734/https://sites.google.com/site/gardeningforbutterflies/asclepias-syriaca|archive-date=July 7, 2015|quote=germination: seed requires cold moist period.}}</ref>

To protect seeds from washing away during heavy rains and from seed-eating birds, one can cover the seeds with a light fabric or with an {{convert|0.5|in|mm|0|adj=on}} layer of [[Mulch#Straw mulch / field hay / salt hay|straw mulch]].<ref>Multiple sources:
* {{cite book|first1=Eric|last1=Mader|first2=Mathew|last2=Shepherd|first3=Mace|last3=Vaughan|first4=Scott Hoffman|last4=Black|first5=Gretchen|last5=LeBuhn|chapter-url=https://archive.org/details/attractingnative0000unse/page/113/mode/1up|year=2011|chapter=Establishing Pollinator Habitat from Seed: Sowing Seed|title=Attracting Native Pollinators: Protecting North America's Bees and Butterflies: The Xerces Society guide|pages=113–114|isbn=978-1-60342-747-0|oclc=776997073|lccn=2010043054|location=[[North Adams, Massachusetts]]|publisher=[[Workman Publishing Company#Storey Publishing|Storey Publishing]]|via=[[Internet Archive]]|access-date=July 7, 2021}}
* {{cite journal|first1=Thomas D.|last1=Landis|first2=R. Kasten|last2=Dumroese|url=https://www.fs.usda.gov/rm/pubs_journals/2015/rmrs_2015_landis_t001.pdf|title=Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat: Propagating Native Milkweeds: Seed Propagation|journal=International Plant Propagators' Society, Combined Proceedings (2014)|year=2015|volume=64|page=302|access-date=July 27, 2025|archive-url=https://web.archive.org/web/20250224032937/https://www.fs.usda.gov/rm/pubs_journals/2015/rmrs_2015_landis_t001.pdf|archive-date=February 24, 2025|url-status=live|via=[[United States Department of Agriculture]]: [[United States Forest Service]]|quote=Any of the standard seed propagation methods (Landis et al., 1999) are effective with milkweed. Direct sowing of non-stratified seeds during the fall followed by exposure to ambient winter conditions can be effective, but the seeds must be mulched and protected. Cover sown seeds with a thin mulch; research has found that common milkweed seeds germinate better when planted 1 to 2 cm (0.4 to 0.8 in.) deep than when at the soil surface (Jeffery and Robison, 1971).}}</ref> However, [[mulch]] acts as an [[Thermal insulation|insulator]]. Thicker layers of mulch can prevent seeds from germinating if they prevent soil temperatures from rising enough when winter ends. Further, few [[seedling]]s can push through a thick layer of mulch.<ref>{{cite book|first1=James|last1=Bush-Brown|first2=Louise|last2=Bush-Brown|year=1958|chapter-url=https://archive.org/details/americasgardenbo00bush_0/page/767/mode/1up|chapter=Chapter 32: Mulches|url=https://archive.org/details/americasgardenbo00bush/page/n2/mode/1up|title=America's Garden Book|page=[https://archive.org/details/americasgardenbo00bush_0/page/768/mode/1up 768]|oclc=597041748|lccn=58005738|publisher=[[Charles Scribner's Sons]]|location= New York|url-access=registration|via=[[Internet Archive]]}}</ref>

Although monarch caterpillars will feed on butterfly weed (''A. tuberosa'') in butterfly gardens, it is typically not a heavily used host plant for the species.<ref>{{cite web|author=Butterfly Society of Virginia|year=2019|title=Growing Milkweed|url=https://www.butterflysocietyofva.org/Growing-Milkweed|access-date=December 25, 2023|archive-url=https://web.archive.org/web/20190624061425/https://www.butterflysocietyofva.org/Growing-Milkweed|archive-date=June 24, 2019|quote=I've grown butterfly weed, swamp milkweed, Asclepias currassavica (bloodflower), Asclepias syriaca (common milkweed), and Asclepias verticillata (whorled milkweed). I've found that butterfly weed is the least favorite of my Monarch guests in my Virginia Beach garden for laying eggs (perhaps the leaves are tougher?)|url-status=live}}</ref> The plant has rough leaves and a layer of [[trichome]]s, which may inhibit oviposition or decrease a female's ability to sense leaf chemicals.<ref name=Gomez>{{cite web|last=Gomez|first=Tony|url=https://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-tuberosa-butterfly-weed/|title=''Asclepias tuberosa'': Butterfly Weed for Monarchs and More|work=Monarch Butterfly Garden|publisher=MonarchButterflyGarden.net|access-date=17 October 2010|quote=Rough leaves for monarch caterpillars, not typically a heavily used host plant|archive-url=https://web.archive.org/web/20160729233805/http://monarchbutterflygarden.net/milkweed-plant-seed-resources/asclepias-tuberosa-butterfly-weed/|archive-date=July 29, 2016|url-status=live}}.{{self-published inline|date=January 2021}}</ref><ref>{{cite journal|first1=Victoria M.|last1=Pocius|first2=Diane M.|last2=Debinski|first3=John M.|last3=Pleasants|first4=Keith G.|last4=Bidne|first5=Richard L.|last5=Hellmich|date=January 8, 2018|title=Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species|doi=10.1002/ecs2.2064|journal=[[Ecosphere (journal)|Ecosphere]] |volume=9|issue=1|pages=1–13|article-number=e02064 |publisher=[[Ecological Society of America]]|bibcode=2018Ecosp...9E2064P |quote=Additionally, ''A. tuberosa'' has a layer of trichomes, which may inhibit oviposition or decrease a female's ability to sense leaf chemicals.|doi-access=free}}</ref> The plant's low levels of cardenolides may also deter monarchs from laying eggs on the plant.<ref>Multiple sources:
* {{cite journal|first1=Victoria M.|last1=Pocius|first2=Diane M.|last2=Debinski|first3=John M.|last3=Pleasants|first4=Keith G.|last4=Bidne|first5=Richard L.|last5=Hellmich|date=January 8, 2018|title=Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species|doi=10.1002/ecs2.2064|journal=[[Ecosphere (journal)|Ecosphere]] |volume=9|issue=1|pages=1–13|article-number=e02064 |publisher=[[Ecological Society of America]]|bibcode=2018Ecosp...9E2064P |quote=In our study, the least preferred milkweed species ''A. tuberosa'' (no choice; Fig. 2) and ''A. verticillata'' (choice; Fig. 3A) both have low cardenolide levels recorded in the literature (Roeske et al., Agrawal et al., Rasmann and Agrawal)|doi-access=free}}
* {{cite web|last=Abugattas|first=Alonzo|url=http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|access-date=July 5, 2021|title=Monarch Way Stations|work=Capital Naturalist|date=January 3, 2017|archive-url=https://web.archive.org/web/20210308084527/http://capitalnaturalist.blogspot.com/2017/01/monarch-way-stations.html|archive-date=March 8, 2021|url-status=live|via=[[Blogger (service)|Blogger]]|quote=If you have hot, dry conditions, then try Butterflyweed (''A. tuberosa'').{{nbsp}}... It is the least favored by monarch caterpillars though because it has very little toxin (cardiac glycosides) in its leaves.}}</ref> While ''A. tuberosa''{{'s}} colorful flowers provide nectar for many adult butterflies, the plant may be less suitable for use in butterfly gardens and monarch waystations than are other milkweed species.<ref name=Gomez/>

Breeding monarchs prefer to lay eggs on swamp milkweed (''A. incarnata'') in the midwest.<ref>{{cite journal|first1=Victoria M.|last1= Pocius|first2=Diane M.|last2=Debinski|first3=John M.|last3=Pleasants|first4=Keith G.|last4=Bidne|first5=Richard L.|last5=Hellmich|date=January 8, 2018|title=Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species|doi=10.1002/ecs2.2064|journal=[[Ecosphere (journal)|Ecosphere]] |volume=9|issue=1|pages=1–13|article-number= e02064|publisher=[[Ecological Society of America]]|bibcode= 2018Ecosp...9E2064P|quote=In no-choice tests, we saw the highest egg counts on ''Asclepias incarnata'' followed by ''Asclepias sullivantii'' and ''Asclepias syriaca'' (Fig. 2). In preference tests, over half of all eggs laid were on ''A. incarnata'' (Fig. 3).|doi-access=free}}</ref> However, ''A. incarnata'' is an [[Ecological succession|early successional plant]] that usually grows at the margins of wetlands and in seasonally flooded areas. The plant is slow to spread via seeds, does not spread by runners, and tends to disappear as vegetative densities increase and habitats dry out.<ref name=survival>{{cite web|url=https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-incarnata/|title=''Asclepias incarnata''|work=Bring Back The Monarchs|publisher=[[Monarch Watch]]|access-date=July 5, 2021|archive-url=https://web.archive.org/web/20210612021725/https://monarchwatch.org/bring-back-the-monarchs/milkweed/milkweed-profiles/asclepias-incarnata/|archive-date=June 12, 2021|url-status=live|quote='''Life span''': In gardens most plants live two-five years but known to survive up to 20 years.{{nbsp}}... '''Propagation''': Slow to spread via seeds.{{nbsp}}... ''''Overhead Conditions''': Not shade tolerant. An early successional plant that tends to grow at the margins of wetlands and in seasonally flooded areas. It is not a good vegetative competitor and tends to disappear as vegetative density increases and habitats dry out.}}</ref> Although ''A. incarnata'' plants can survive up to 20 years, most live only two to five years in gardens. The species is not shade-tolerant and is not a good vegetative competitor.<ref name=survival/>

== See also ==
* [[Butterfly house (conservatory)|Butterfly house]]
* [[Lepidoptera migration]]
* [[Peninsula Point Light]], Michigan

== References ==
{{Ibid|date=October 2024}}
{{Reflist
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== External links ==
{{Commons category|Danaus plexippus}}
{{Wikispecies|Danaus plexippus}}
{{Wikisource|Mimicry in Butterflies}}
* [http://australianmuseum.net.au/Wanderer-Butterfly/ Australian Museum fact sheet on monarch butterflies]
* [http://www.mission-monarch.org/ Mission Monarch (Canada)]
* [https://www.youtube.com/watch?v=ocWgSgMGxOc Monarch butterfly metamorphosis: time-lapse video (2:42 minutes)]
* [http://entomology.ifas.ufl.edu/creatures/bfly/monarch.htm Monarch butterfly] on the [[University of Florida|UF]] / [[Institute of Food and Agricultural Sciences|IFAS]] Featured Creatures website
* [http://www.monarchjointventure.org Monarch Joint Venture] – Partnering Across the U.S. to Conserve the Monarch Butterfly Migration
* [https://web.archive.org/web/20171206235416/http://learner.org/jnorth/monarchs Monarch migration maps]
* [http://www.monarchwatch.org/ Monarch Watch]
* [https://www.pbs.org/wgbh/nova/butterflies/ PBS ''Nova'' documentary "The Incredible Journey of the Butterflies"]
* [https://web.archive.org/web/20071012001216/http://www.butterfliesandmoths.org/species?l=1892 USGS description of monarch butterfly]
* [http://explorer.natureserve.org/servlet/NatureServe?searchSciOrCommonName=monarch+butterfly&x=0&y=0 Monarch butterfly data at NatureServe Explorer]

{{Taxonbar |from=Q212398}}
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{{DEFAULTSORT:Monarch (Butterfly)}}
[[Category:Danaus (butterfly)]]
[[Category:Animal migration]]
[[Category:Aposematic species]]
[[Category:Articles containing video clips]]
[[Category:Butterflies described in 1758]]
[[Category:Butterflies of Central America]]
[[Category:Butterflies of Europe]]
[[Category:Butterflies of North America]]
[[Category:Butterflies of Oceania]]
[[Category:Butterflies of Cuba]]
[[Category:Endangered fauna of California]]
[[Category:Fauna of the California chaparral and woodlands]]
[[Category:Insects of Hawaii]]
[[Category:Nymphalidae of South America]]
[[Category:Poisonous animals]]
[[Category:Symbols of Alabama]]
[[Category:Symbols of Idaho]]
[[Category:Symbols of Illinois]]
[[Category:Symbols of West Virginia]]
[[Category:Animal taxa named by Carl Linnaeus]]
[[Category:Lepidoptera of the United States]]
[[Category:Lepidoptera of Mexico]]
[[Category:Lepidoptera of New Guinea]]