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{{Short description|Largest living species of lizard in the United States}}
{{For|the song|Gila Monster (song)}}
{{Good article}}
{{Speciesbox
| image = Gila monster2.JPG
| image_caption = In the [[American International Rattlesnake Museum]], [[New Mexico]] 
| status = NT
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=Hammerson, G.A. |author2=Frost, D.R. |author3=Gadsden, H. |date=2007 |title=''Heloderma suspectum'' |volume=2007 |page=e.T9865A13022716 |doi=10.2305/IUCN.UK.2007.RLTS.T9865A13022716.en |access-date=19 November 2021}}</ref>
| status2 = CITES_A2
| status2_system = CITES
| status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>
| genus = Heloderma
| species = suspectum
| authority = [[Edward Drinker Cope|Cope]], 1869
}}
[[File:Gila Monster.webm|thumb|A Gila monster]]

The '''Gila monster''' ('''''Heloderma suspectum''''', {{IPAc-en|ˈ|h|iː|l|ə}} {{respell|HEE|lə}}) is a species of [[venom]]ous [[lizard]] native to the [[Southwestern United States]] and the northwestern [[Mexico|Mexican]] state of [[Sonora]]. It is a heavy, slow-moving reptile, up to {{Convert|56|cm|in}} long, and it is the only venomous lizard native to the United States. Its venomous close relatives, the four [[Mexican beaded lizard|beaded lizards]] (all former subspecies of ''[[Heloderma horridum]]'') inhabit Mexico and [[Guatemala]].<ref name=":0" /><ref name=":6">{{Cite book|author1=Bogert, Charles M. |author2=Rafael Martin del Campo |title=The Gila Monster and its allies: the relationships, habits, and behavior of the lizards of the Family Helodermatidae |publisher=Bulletin of the American Museum of Natural History|year=1956|isbn=|location=New York|pages=}}</ref> The Gila monster is sluggish in nature, so it is not generally dangerous and very rarely poses a real threat to humans. However, it has a fearsome reputation and is sometimes killed despite the species being protected by state law in [[Arizona]].<ref name="iucn status 19 November 2021" /><ref name="ITIS">{{ITIS |id=174113 |taxon=''Heloderma suspectum'' |access-date=19 May 2008}}</ref>

== History ==
[[File:Kladoramm heloderma.jpg|alt=Evolutionary splitting of the genus ''Heloderma'' into species|right|thumb|Evolutionary splitting of the genus ''Heloderma'' into species (Reiserer et al)<ref>{{Cite journal|author1=R. S. Reiserer |author2=G. W. Schuett |author3=D. D. Beck |date=2013 |title=Taxonomic Reassessment and conservation status of the beaded lizard, Heloderma horridum (Squamata Helodermatidae) |journal=Amphibian & Reptile Conservation |volume=7 |pages=74–96}}</ref>
{| class="wikitable"
! colspan="2" |Explanation of the numbers
|-
|1
|Late Eocene (about 35 million years)
|-
|2
|Late Miocene (about 10 million years)
|-
|3
|Pliocene (about 4.4 million years)
|-
|4
|Pliocene (about 3.0 million years)
|}
]]
The name "Gila" refers to the [[Gila River]] Basin in the U.S. states of Arizona and [[New Mexico]], where the Gila monster was once plentiful.<ref>{{cite web |url=http://www.etymonline.com/index.php?search=gila+monster&searchmode=none |title=Online Etymology Dictionary |access-date=2008-06-10 |archive-date=2008-12-11 |archive-url=https://web.archive.org/web/20081211061342/http://www.etymonline.com/index.php?search=gila+monster&searchmode=none |url-status=live }}</ref> ''Heloderma'' means "studded skin", from the [[Ancient Greek]] words {{transliteration|grc|helos}} ({{lang|grc|ἧλος}}), "the head of a nail or stud", and {{transliteration|grc|derma}} ({{lang|grc|δέρμα}}), "skin". The species epithet ''suspectum'' comes from the describer, paleontologist [[Edward Drinker Cope]]. At first, this new specimen of ''Heloderma'' was misidentified and considered to be a northern variation of the beaded lizard already known to live in Mexico. He suspected that the lizard might be venomous due to the grooves in the teeth.<ref name=":7" />
[[File:Erste-krustenechse.jpg|alt=The first drawing of Gila monster from 1857|thumb|The first drawing of a Gila monster by Baird, S. F. (1857)<ref name=":7">{{Cite journal|last=Baird|first=S. F.|date=1859|title=Reptiles of the boundary, with notes by the naturalists on the survey|journal=United States and Mexican Boundary Survey Under the Order of Lieut. Col. W.H. Emory |volume=3 |pages=1–35}}</ref>]]
The Gila monster is the largest extant lizard species native to North America north of the Mexican border. Its [[Snout–vent length|snout-to-vent length]] ranges from {{convert|26|to|36|cm|in|abbr=on}}. The tail is about 20% of the body size, and the largest specimens may reach {{convert|51|to|56|cm|in|abbr=on}} in total length. Body mass is typically in the range of {{convert|550|to|800|g|lb|abbr=on}}. They appear strong in their body structure with a stout snout, massive head, and "little"-appearing eyes, which can be protected by a [[nictitating membrane]].<ref name="Christel et al. 2007">{{cite journal |vauthors=Christel CM, DeNardo DF, Secor SM|date=October 2007 |title=Metabolic and digestive response to food ingestion in a binge-feeding lizard, the Gila monster (''Heloderma suspectum'') |journal=Journal of Experimental Biology|volume=210|issue=19|pages=3430–3439|doi=10.1242/jeb.004820|pmid=17872997|doi-access=free}}</ref><ref>{{cite journal|last1=Davis|first1=Jon R.|last2=DeNardo |first2=Dale F. |year=2010 |title=Seasonal patterns of body condition, hydration state, and activity of Gila monsters (''Heloderma suspectum'') at a Sonoran Desert site |journal=Journal of Herpetology |volume=44 |issue=1 |pages=83–93 |doi=10.1670/08-263.1 |s2cid=6808861}}</ref><ref name=":0">{{cite book |last=Beck |first=D. D. |year=2005 |title=Biology of Gila monsters and beaded lizards |volume=9 |publisher=University of California Press}}</ref>

The Gila monster has four close living relatives, all of which are beaded lizards. There are three species in Mexico: ''[[Heloderma exasperatum]]'', ''[[Heloderma horridum]]'' and ''[[Heloderma alvarezi]]'', as well as another species in Guatemala: ''[[Heloderma charlesbogerti]]''.<ref name=":0" /><ref name=":6" />

The evolutionary history of the Helodermatidae may be traced back to the [[Cretaceous]] period (145 to 166 million years ago), when ''[[Gobiderma|Gobiderma pulchrum]]'' and ''[[Estesia|Estesia mongolensis]]'' were present. The genus ''Heloderma'' has existed since the [[Miocene]], when ''H. texana'' lived. Fragments of [[osteoderm]]s from the Gila monster have been found in Late [[Pleistocene]] (10,000 to 8,000 years ago) deposits near [[Las Vegas|Las Vegas, Nevada]]. Because the helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as [[living fossil]]s. Although the Gila monster appears closely related to the [[monitor lizard]]s (varanids) of Africa, Asia, and Australia, their wide geographical separation and distinct features indicate that ''Heloderma'' is better placed in a separate family.<ref name="mattison">{{cite book |author=Mattison, Chris |title=Lizards of the World |publisher=Blandford |location=London |year=1998 |isbn=0713723572 |url=https://archive.org/details/lizardsofworld00matt }}</ref>

== Skin ==
[[File:Gila monster ncd 2012.jpg|thumb|upright=1.15|A plate from the'' Century Cyclopedia'' that depicts the Gila monster]]
[[File:Gila fg01.jpg|alt=The dorsal skin of a Gila monster|thumb|The dorsal skin of a Gila monster]]
[[File:Totalhäutung einer Gila Krustenechse.jpg|alt=The total molt of a female Gila monster about 2 weeks before egg-laying|thumb|The total molt of a female Gila monster about 2 weeks before egg-laying]]
The scales of the head, back, and tail contain little pearl-shaped bones (osteoderms) similar to those found in the beaded lizards from farther south. The scales of the belly are free from osteoderms. Female Gila monsters go through a total shed lasting about 2 weeks before depositing their eggs. The dorsal part is often shed in one large piece. Adult males normally shed in smaller segments in August. The young seem to be in constant shed. Adults have more or less yellow to pink colors on a black surface. Hatchlings have a uniform, simple, and less colorful pattern. This drastically changes within the first 6 months of their lives.<ref name=":4" /> Hatchlings from the northern area of the species' distribution have a tendency to retain most of their juvenile pattern. It has also been seen that Gila monsters in areas with darker rocks and substrate will have darker colorations.<ref name=":10" />

The heads of males are very often larger and more triangular-shaped than in females. The length of the tail of the two sexes is statistically very similar, so it does not help in differentiation of the sexes.<ref>{{Cite journal|author1=Gienger, C. M. |author2=Beck, Daniel D. |date=2007|title=Heads or tails? Sexual dimorphism in helodermatid lizards|url=|journal=Canadian Journal of Zoology|volume=85|pages=92–95|doi=10.1139/z06-198}}</ref> Individuals with stout tail ends occur in both nature and under human breeding.

== Distribution and habitat ==
[[File:Gila Monster head.jpg|thumb|right|The head of a Gila monster with bead-like scales and strong forelegs and claws suitable for digging]]
The Gila monster is found in the Southwestern United States and Mexico, across a range including Sonora, Arizona, and parts of [[California]], [[Nevada]], [[Utah]], and New Mexico. No records have been given from [[Baja California]].<ref name=":0" /> They inhabit [[scrubland]], succulent desert, and oak woodland, seeking shelter in burrows, thickets, and under rocks in locations with a favorable [[microclimate]] and adequate humidity. Gila monsters rely heavily on the use of shelters and spend much of their time dwelling there.<ref>{{Cite journal |last1=Davis |first1=Jon R. |last2=Denardo |first2=Dale |date=November–December 2009 |title=Water supplementation affects the behavioral and physiological ecology of Gila monsters (Heloderma suspectum) in the Sonoran desert |journal=Physiological and Biochemical Zoology |volume=82 |issue=6 |pages=739–748 |url=http://www.scopus.com/inward/record.url?scp=73449136873&partnerID=8YFLogxK |doi=10.1086/605933 |pmid=19799522 |s2cid=30275597 |issn=1522-2152|url-access=subscription }}</ref> Often times these shelters are in rocky areas in Navajo Sandstone and basaltic lava flows.<ref name=":10">{{Cite journal |last=Beck |first=Daniel D. |date=1990 |title=Ecology and Behavior of the Gila Monster in Southwestern Utah |jstor=1564290 |journal=Journal of Herpetology |volume=24 |issue=1 |pages=54–68 |doi=10.2307/1564290 |issn=0022-1511}}</ref> Gila monsters depend on water resources and can be observed in puddles of water after a summer rain. They avoid living in open areas, such as flats and open grasslands.<ref name=":0" />

== Ecology ==
[[File:Echse auf Handschuh.jpg|thumb|A Gila monster in captivity]]
Gila monsters spend 90% of their lifetime underground in burrows or rocky shelters.<ref name=":0" /> They are active in the morning during the dry season (spring and early summer). The lizards move to different shelters every 4–5 days up to the beginning of the summer season. By doing so, they optimize for a suitable microhabitat.<ref name=":0" /><ref name=":1">{{Cite journal |last1=DeNardo |first1=DF |last2=Moeller |first2=KT |last3=Seward |first3=M |last4=Repp |first4=R |date=2018 |title=Evidence for atypical nest overwintering by hatchling lizards, Heloderma suspectum |journal=Proceedings of the Royal Society |volume=285 |issue=1879 |doi=10.1098/rspb.2018.0632 |pmid=29794051 |pmc=5998102 |doi-access=free}}</ref><ref name=":3">{{Cite journal |last1=Beck |first1=D.D. |first2=R.D. |last2=Jennings|date=2003|title=Habitat use by Gila Monsters. The importance of shelters |journal=Herpetological Monographs |volume=17 |pages=112–130 |doi=10.1655/0733-1347(2003)017[0111:HUBGMT]2.0.CO;2 |s2cid=54904180}}</ref> Later in the summer, they may be active on warm nights or after a [[thunderstorm]]. They maintain a surface body temperature of about {{convert|30|C|F}}.<ref name=":0" /> Close to {{cvt|37|C|F}}, they are able to decrease their body temperature by up to 2&nbsp;°C (3.6&nbsp;°F) by an activated, limited evaporation via the cloaca.<ref name=":2">{{Cite journal |last1=DeNardo |first1=Dale F. |last2=Zubal |first2=Tricia E. |last3=Hoffman |first3=Ty C. M. |date=2004 |title=Cloacal evaporative cooling: a previously undescribed means of increasing evaporative water loss at higher temperatures in a desert ectotherm, the Gila monster Heloderma suspectum |journal=The Journal of Experimental Biology |volume=207 |issue=Pt 6 |pages=945–953 |doi=10.1242/jeb.00861 |pmid=14766953 |doi-access=|s2cid=24183761 }}</ref> One study investigating a population of Gila monsters in southwestern Utah noted that the lizard's activity peaked from late April to mid June. The average distance traveled during their bouts of activity was {{Convert|210|m|ft}}, but on occasion some lizards would travel distances greater than {{Convert|1|km|mi}}. During the Gila monster's active season of approximately 90 days, only ten days were spent active.<ref name=":10"/> Gila monsters are slow sprinters, but they have relatively high endurance and maximal aerobic capacity ([[VO2max|VO<sub>2</sub> max]]) compared to other lizards.<ref name='Becketal1985'>{{cite journal |last1=Beck |first1=D. D. |first2=M. R. |last2=Dohm |first3=T. Jr. |last3=Garland |first4=A. |last4=Ramirez-Bautista |first5=C. H. |last5=Lowe |year=1985 |title=Locomotor performance and activity energetics of helodermatid lizards |journal=Copeia |volume=1995 |issue=3 |pages=577–585 |doi=10.2307/1446755 |jstor=1446755}}</ref> They are preyed upon by [[coyote]]s, [[badger]]s and [[Raptor (bird)|raptor]]s. Hatchlings are preyed on by snakes, such as [[kingsnake]]s (''Lampropeltis'' sp.).

Among adaptations to a dry environment is a slow metabolism, allowing them to use less than half the amount of energy expected for lizards of their size.<ref>[https://bioone.org/journals/copeia/volume-2014/issue-2/CP-13-086/Life-in-the-Lizard-Slow-Lane--Gila-Monsters-Have/10.1643/CP-13-086.short Life in the Lizard Slow Lane: Gila Monsters Have Low Rates of Energy Use and Water Flux]</ref> Gila monsters, and possibly also the [[Mexican beaded lizard]], store water in their [[Bladder#Reptiles|urinary bladder]] and reabsorb it across the bladder epithelium. Their tail is used for energy storage in the form of fat.<ref>{{cite thesis|url=https://digitalcommons.cwu.edu/cgi/viewcontent.cgi?article=1937&context=etd|title=Thermal and Behavioral Ecology of the Mexican Beaded Lizard (Heloderma horridum)|last=Holcomb|first=Terry|type=MSc|year=2017|publisher=Central Washington University}}</ref>

== Diet ==
The Gila monster's diet consists of a variety of food items – small [[mammal]]s (such as young [[rabbit]]s, [[hare]]s, [[Mouse|mice]], [[ground squirrel]]s, and other [[rodent]]s), small [[bird]]s, [[snake]]s, lizards, [[frog]]s, [[insect]]s, other [[invertebrate]]s, [[carrion]], and the [[egg]]s of birds, lizards, snakes, and [[tortoise]]s.<ref>{{Cite web|url=https://a-z-animals.com/animals/gila-monster/|title=Gila Monster|date=10 September 2018 |access-date=2021-05-30|archive-date=2021-06-02|archive-url=https://web.archive.org/web/20210602213557/https://a-z-animals.com/animals/gila-monster/|url-status=live}}</ref><ref>{{Cite web |title=Heloderma suspectum (Gila Monster) |website=[[Animal Diversity Web]] |url=https://animaldiversity.org/accounts/Heloderma_suspectum/ |access-date=2020-12-19 |archive-date=2021-02-12|archive-url=https://web.archive.org/web/20210212233207/https://animaldiversity.org/accounts/Heloderma_suspectum/|url-status=live}}</ref><ref name=":8">{{Cite journal |last1=Zylstra |first1=E.T. |last2=Seward |first2=M.T. |last3=Schuett |first3=G.W. |last4=Repp |first4=R. |last5=DeNardo|first5=D.F.|last6=Beck |first6=D.D. |date=2015 |title=Heloderma suspectum (Gila Monster), Probable Courtship and Mating Behavior |journal=Herpetological Review |volume=46 |pages=258–259 |via=}}</ref><ref>{{Cite web |url=https://www.desertmuseum.org/books/nhsd_gila.php |title=Gila Monster (Heloderma suspectum) |access-date=2021-03-07 |archive-date=2021-03-03 |archive-url=https://web.archive.org/web/20210303181810/https://www.desertmuseum.org/books/nhsd_gila.php|url-status=live}}</ref><ref>{{Cite web |title=Foothills Palo Verde Fact Sheet |url=https://www.desertmuseum.org/kids/oz/long-fact-sheets/Gila%20Monster.php |access-date=2021-03-07 |archive-date=2021-03-21 |archive-url=https://web.archive.org/web/20210321185343/https://www.desertmuseum.org/kids/oz/long-fact-sheets/Gila%20Monster.php |url-status=live}}</ref> Three to four extensive meals in spring are claimed to give them enough energy for a whole season.<ref>{{Cite web |title=Gila monster |url=https://nationalzoo.si.edu/animals/gila-monster |access-date=April 25, 2023 |website=Smithsonian's National Zoo & Conservation Biology Institute}}</ref><ref>{{Cite web |last=Mozdy |first=Michael |date=March 22, 2017 |title=Gila: the Monster, the Myth, the Legend |url=https://nhmu.utah.edu/blog/2017/03/22/gila-monster-myth-legend |access-date=April 25, 2023 |website=Natural History Museum of Utah}}</ref><ref name=":10" /> They can store fat in their tails and therefore do not need to eat often.<ref name=":11">{{Cite web |title=Gila Monster |url=https://www.nationalgeographic.com/animals/reptiles/facts/gila-monster |archive-url=https://web.archive.org/web/20210223194637/https://www.nationalgeographic.com/animals/reptiles/facts/gila-monster |url-status=dead |archive-date=February 23, 2021 |access-date=April 25, 2023 |website=National Geographic}}</ref> Nevertheless, they feed whenever they come across suitable prey. Young Gila monsters can swallow up to 50% of their body weight in a single meal.<ref name=":2" /> Adults may eat up to one third of their body weight in one meal.<ref name="Christel et al. 2007" />

The Gila monster uses its extremely acute sense of smell to locate prey. The strong, two-ended tipped tongue, which is pigmented in black-blue colors,<ref name=":4">{{Cite book |last=Schwandt|first=Hans-Joachim|title=The Gila Monster – Heloderma suspectum |publisher=Edition Chimaira|year=2019 |isbn=978-3-89973-441-6|location=Frankfurt / Main}}</ref> picks up scent molecules to be transferred to the opening of the [[Vomeronasal organ|Jacobson organ]] around the middle of the upper mouth cavern.

Prey may be crushed to death if large, or eaten alive, most of the time head first, and helped down by muscular contractions and neck flexing. After food has been swallowed, the Gila monster may immediately resume tongue flicking and search behavior for identifying more prey such as eggs or young in nests. Gila monsters are able to climb trees, [[cactus|cacti]], and even fairly straight, rough-surfaced walls.<ref name=":0"/><ref>{{Cite journal |last1=Repp |first1=Roger A. |last2=Schuett |first2=Gordon W. |date=2010 |title=Heloderma suspectum (Gila monster). Tree-climbing |journal=Herpetological Review |volume=41 |issue=4 |pages=491–492}}</ref>

== Venom ==
{{quote box
| source = —Dr. Ward, ''Arizona Graphic'', September 23, 1899
| align = right
| width = 33%
| quote="I have never been called to attend a case of Gila monster bite, and I don't want to be. I think a man who is fool enough to get bitten by a Gila monster ought to die. The creature is so sluggish and slow of movement that the victim of its bite is compelled to help largely in order to get bitten."|Dr. Ward, ''Arizona Graphic'', September 23, 1899
}}

=== Pioneer beliefs ===
In the [[American frontier|Old West]], the pioneers believed a number of myths about the Gila monster, including that the lizard had foul or toxic breath and that its bite was fatal.<ref name=lapidus>{{cite web|last=Lapidus|first=Richard|title=The Gila Monster Had a Killer Reputation|url=http://www.historynet.com/the-gila-monster-had-a-killer-reputation.htm|publisher=Wild West Magazine |quote=Although the Gila monster's bite is extremely painful, none has resulted in a verifiable human fatality to a healthy person. |access-date=10 March 2013|date=June 3, 2011|archive-date=22 January 2013|archive-url=https://web.archive.org/web/20130122015744/http://www.historynet.com/the-gila-monster-had-a-killer-reputation.htm|url-status=live}}</ref> ''[[The Tombstone Epitaph]]'' of [[Tombstone, Arizona]], wrote about a Gila monster that a local person caught on May 14, 1881:

{{Blockquote|text=This is a monster, and no baby at that, it being probably the largest specimen ever captured in Arizona. It is 27 inches long and weighs 35 lb. It was caught by H. C. Hiatt on the road between Tombstone and Grand Central Mill, and was purchased by Messrs. Ed Baker and Charles Eastman, who now have it on exhibition at Kelley's Wine House, next door above Grand Hotel, Allen Street. Eastern people who have never seen one of these monsters should not fail to inspect his Aztecship, for they might accidentally stumble upon one some fine day and get badly frightened, except they know what it is.|author=|title=|source=}}

On May 8, 1890, southeast of [[Tucson, Arizona|Tucson]], [[Arizona Territory]], Empire Ranch owner [[Walter Vail]] captured and thought he had killed a Gila monster. He tied it to his saddle and it bit the middle finger of his right hand and would not let go. A ranch hand pried open the lizard's mouth with a pocket knife, cut open his finger to stimulate bleeding, and then tied saddle strings around his finger and wrist. They summoned Dr. John C. Handy of Tucson, who took Vail back to Tucson for treatment, but Vail experienced swollen and bleeding [[lymph nodes|glands]] in his throat for sometime afterward.<ref name=lapidus />

Dr. Handy's friend, Dr. [[George E. Goodfellow|George Goodfellow]] of Tombstone, was among the first to research the actual effects of Gila monster venom. ''[[Scientific American]]'' reported in 1890, "The breath is very fetid, and its odor can be detected at some little distance from the lizard. It is supposed that this is one way in which the monster catches the insects and small animals which form a part of its food supply{{snd}}the foul gas overcoming them." Goodfellow offered to pay local residents $5.00 for Gila monster specimens. He bought several and collected more on his own. In 1891, he purposely provoked one of his captive lizards into biting him on his finger. The bite made him ill and he spent the next five days in bed, but he completely recovered. When ''Scientific American'' ran another ill-founded report on the lizard's ability to kill people, he wrote in reply and described his own studies and personal experience. He wrote that he knew several people who had been bitten by Gila monsters but had not died from the bite.<ref name=lapidus />

=== Venom delivery ===
[[File:Gebiss mit Ersatzzähnen.jpg|alt=Venom Grooves and position of the exchange teeth|thumb|Venom grooves and position of the exchange teeth]]
[[File:Gila-skull-1.jpg|alt=Gila monster Skull showing dentition|thumb|Gila monster skull showing dentition (osteoderms are fused with the forehead), photo by A. Laube]]
The Gila monster produces venom in modified [[salivary glands]] at the end of its lower jaws, unlike snakes, whose venom is produced in glands behind the eyes.<ref>{{Cite journal |last=West |first=G. S. |date=1895 |title=On the Buceal-Glands and Teeth of certain poisonous Snakes |journal=Proceed. Zool. Soc. Of London |volume= |pages=}}</ref> The Gila monster lacks strong musculature in glands above the eyes; instead, in ''Heloderma'', the venom is propelled from the gland via a tubing to the base of the lower teeth and then by capillary forces into two grooves of the tooth and then chewed into the victim.<ref name=":0" /><ref name=":11" /> The teeth are tightly anchored to the jaw ([[pleurodont]]). Broken and regular replacement teeth have to wait every time to go into position in a determinate "wavelike" sequence. They change/replace their teeth during their entire life.<ref>{{Cite journal |last=Odermatt, C. (Buochs) |date=1940 |title=Beiträge zur Kenntnis des Gebisses von Heloderma |journal=Vierteljahresschrift der Naturforschenden Gesellschaft in Zürich |volume=LXXXV}}</ref><ref>{{Cite book |last=Edmund |first=A. G. |title=Biology of the Reptilia |publisher=Academic Press |year=1969 |location=London |pages=117–200}}</ref> The Gila monster's bright colors might be suitable to teach predators not to bother this "painful" creature. Because the Gila monster's prey consists mainly of eggs, small animals, and otherwise "helpless" prey, the Gila monster's venom is thought to have evolved for defensive rather than for hunting use.<ref name=":10"/>

=== Toxicity ===
The venom of a Gila monster is normally not fatal to healthy adult humans.<ref name=lapidus /> One fatality has been confirmed since 1930, on February 16, 2024,<ref>{{cite web | url=https://kdvr.com/news/local/lakewood-man-dies-after-being-bitten-by-pet-gila-monster/?ipid=promo-link-block1 | archive-url=https://web.archive.org/web/20240301210735/https://kdvr.com/news/local/lakewood-man-dies-after-being-bitten-by-pet-gila-monster/?ipid=promo-link-block1 | archive-date=2024-03-01 | title=Lakewood man dies after being bitten by pet Gila monster | date=20 February 2024 }}</ref> and the rare fatalities recorded before 1930 occurred in adults who were intoxicated by alcohol or had mismanaged the treatment of the bite.<ref name="StrimpleTomassoni1997">{{cite journal|last1=Strimple|first1=Peter D.|last2=Tomassoni|first2=Anthony J.|last3=Otten|first3=Edward J.|last4=Bahner|first4=David|title=Report on envenomation by a Gila monster (Heloderma suspectum) with a discussion of venom apparatus, clinical findings, and treatment|journal=Wilderness & Environmental Medicine|volume=8|issue=2|year=1997|pages=111–116|issn=1080-6032|doi=10.1580/1080-6032(1997)008[0111:ROEBAG]2.3.CO;2|pmid=11990142|doi-access=free}}</ref> The Gila monster can bite quickly and may not release the victim without intervention. If bitten, the victim may attempt to fully submerge the lizard in water, pry the jaws open with a knife or stick, or physically yank the lizard free. While pulling the lizard directly increases risk of severe lacerations from the lizard's sharp teeth, it may also mitigate envenomation. Symptoms of the bite include excruciating pain, edema, and weakness associated with a rapid drop in blood pressure.

YouTuber [[Coyote Peterson]] described the bite as "like hot lava coursing through your veins" and claimed it was "the worst pain [he] had ever experienced". It is generally regarded as the most painful venom produced by any vertebrate.<ref>{{Citation|last=Brave Wilderness|title=Gila Monster BITE!|date=2015-12-01|url=https://www.youtube.com/watch?v=swlozUKuvFI|access-date=2018-09-21|archive-date=2019-01-15|archive-url=https://web.archive.org/web/20190115022335/https://www.youtube.com/watch?v=swlozUKuvFI|url-status=live}}</ref>

More than a dozen [[peptide]]s and other substances have been isolated from the Gila monster's venom, including [[hyaluronidase]], [[serotonin]], [[phospholipase]] A<sub>2</sub>, and several [[kallikrein]]-like [[glycoprotein]]s responsible for the pain and edema caused by a bite, without producing a [[compartment syndrome]]. Four potentially lethal toxins have been isolated from the Gila monster's venom, which cause [[hemorrhage]] in internal organs and exophthalmos (bulging of the eyes),<ref>{{Cite web |url=http://www.herpetology.com/helobite.txt |title=Poisindex (R) Toxilogic Managements: Topic: Gila Monster (Heliderma Suspectum) |access-date=2010-08-05 |archive-date=2010-12-03 |archive-url=https://web.archive.org/web/20101203064210/http://herpetology.com/helobite.txt |url-status=live }}</ref> and [[helothermine]], which causes [[lethargy]], partial [[paralysis]] of the limbs, and [[hypothermia]] in [[rat]]s. Some are similar in action of the [[vasoactive intestinal peptide]] (VIP), which relaxes [[smooth muscle]] and regulates water and [[electrolyte]] secretion between the [[small intestine|small]] and [[large intestine]]s. These bioactive peptides are able to bind to VIP receptors in many different human tissues. One of these, helodermin, has been shown to inhibit the growth of [[lung cancer]].<ref>{{cite journal |vauthors=Maruno K, Said SI |title=Small-cell lung carcinoma: inhibition of proliferation by vasoactive intestinal peptide and helodermin and enhancement of inhibition by anti-bombesin antibody |journal=Life Sciences |volume=52 |issue=24 |pages=PL267–271 |year=1993 |pmid=8389407 |doi= 10.1016/0024-3205(93)90640-O}}</ref><ref>{{cite web|last=Clarke|first=Toni|title=Gila Monster Spit May Yield Alzheimer's Drug|url=http://www.jcrows.com/gilamonster.html|access-date=2011-05-29|archive-date=2011-07-18|archive-url=https://web.archive.org/web/20110718033543/http://www.jcrows.com/gilamonster.html|url-status=live}}</ref>
In February 2024, a Colorado man died after sustaining a 4 minute long bite from a pet Gila monster. Autopsy reports determined cause of death to come from the animal bite/venom.<ref>{{Cite news |url= https://www.nytimes.com/2024/03/16/us/gila-monster-bite-death.html|title=Colorado Man Died from Venomous Gila Monster Bite, Autopsy Confirms |work=The New York Times |date=16 March 2024 |last1=Ortiz |first1=Aimee }}</ref>

=== Relationship to GLP-1 agonists ===
{{Main article|GLP-1 agonist}}
The constituents of ''H. suspectum'' venom that have received the most attention from researchers are the bioactive peptides, including helodermin, helospectin, exendin-3, and exendin-4.<ref>{{cite journal|vauthors=Aird SD|date=June 2008|title=Nucleoside composition of Heloderma venoms|journal=Comparative Biochemistry and Physiology B|volume=150|issue=2|pages=183–186 |doi=10.1016/j.cbpb.2008.02.012|pmid=18430599}}</ref> Exendin-4, which is specific for ''H. suspectum'', has formed the basis of a class of medications for the treatment of [[type 2 diabetes]] and [[obesity]]/[[metabolic syndrome]], known as the [[GLP-1 receptor agonist]]s.

In 2005, the U.S. [[Food and Drug Administration]] approved the drug [[exenatide]] (marketed as Byetta) for the management of type 2 diabetes. It is a synthetic modification of the protein exendin-4, that was originally isolated from the Gila monster's venom.<ref name="Baylor">{{cite journal|last=Bond|first=Aaron | title=Exenatide (Byetta) as a novel treatment option for type 2 diabetes mellitus|journal=Baylor University Medical Center Proceedings|volume=19|issue=3 | pages=281–284|date=July 2006|doi=10.1080/08998280.2006.11928181 |pmid=17252050|pmc=1484540}}</ref><ref>{{Cite journal|author1=Chen, Tianbao H.K. |author2=Kwok, C. |author3=Ivanyi, Cristipher Shae|date=2006|title=Isolation and cloning of exendin precursor cDNAs from single samples of venom from the Mexican beaded lizard (Heloderma horridum) and the Gila monster (Heloderma suspectum) |journal=Toxicon|volume=47-3|issue=3|pages=288–295 |doi=10.1016/j.toxicon.2005.11.004|pmid=16386282|bibcode=2006Txcn...47..288C }}</ref> In a 3-year study with people with type 2 diabetes, exenatide showed healthy sustained [[glucose]] levels. The effectiveness is because the lizard protein is 53% identical to [[glucagon-like peptide-1]] analog (GLP-1), a hormone released from the human digestive tract that helps to regulate [[insulin]] and [[glucagon]]. GLP-1 not only increases insulin secretion but increases β-cell proliferation and survival.<ref>{{Cite journal |last=Furman |first=Brian L. |date=2012-03-15 |title=The development of Byetta (exenatide) from the venom of the Gila monster as an anti-diabetic agent |url=https://www.sciencedirect.com/science/article/abs/pii/S0041010110004472?via=ihub |journal=Toxicon |series=From venoms to drugs |volume=59 |issue=4 |pages=464–471 |doi=10.1016/j.toxicon.2010.12.016 |issn=0041-0101|url-access=subscription }}</ref> Using a sophisticated injection formula with sustained release of the drug, the lizard protein remains effective much longer than the human hormone. This helps diabetics keep their blood glucose levels under control for a week by a single injection. Exenatide also slows the emptying of the stomach and causes a decrease in appetite, contributing to weight loss.<ref name="drug">{{cite news|title=Drug Derived From Gila Monster Saliva Helps Diabetics Control Glucose, Lose Weight|publisher=Science Daily|url=https://www.sciencedaily.com/releases/2007/07/070709175815.htm|date=2007-07-12|access-date=2018-02-28|archive-url=https://web.archive.org/web/20180323044354/https://www.sciencedaily.com/releases/2007/07/070709175815.htm |archive-date=2018-03-23|url-status=live}}</ref>

== Life cycle ==
The Gila monster emerges from [[brumation]] in early March. Gila monsters sexually mature at 4–5 years old. It mates in April and May.<ref name=":0" /> The male initiates courtship by flicking his tongue to search for the female's scent. If the female rejects his advances, she will bite him and chase him away. When successful, copulation has been observed in captivity to last from 15 minutes to two and a half hours. There is only a single record of attempted mating outside of a shelter.<ref name=":8" /> The female lays eggs at the end of May into June. A clutch may consist of up to eight (rarely more than six) eggs.<ref name=":0" /><ref name=":4" /> The incubation in captivity lasts about 5 months, depending on the incubation temperature. The hatchlings are about {{cvt|16|cm|in}} long and can bite and inject venom as soon as they are hatched.

The egg development and hatching time of young in the wild has been a subject of ongoing speculation. The first model stated that youngsters hatch in fall and stay underground. The second theory postulated a nearly developed embryo remains inside the egg over winter and hatches in spring. Hatchlings (weight about {{cvt|35|g}}) are observed at the end of April to early June.

Discussions of the exact egg development and hatching cycle of the Gila monster came to an abrupt and unexpected end on October 28, 2016, when a backhoe was digging at the outer walls of a house in a suburb of northern [[Tucson, Arizona|Tucson]]. The backhoe extracted a nest of a female Gila monster with five eggs in the process of hatching. The Gila monster is now known to hatch near the end of October and immediately proceed into hibernation without surfacing.<ref name=":1" /> They then appear on the surface from May through June the following year when prey should be abundant.

In summer, Gila monsters gradually spend less time on the surface to avoid the hottest part of the season; occasionally, they may be active at night. Females that have laid eggs are exhausted and thin, fighting for survival, and have to spend extra effort to "reconstitute". The brumation of Gila monsters begins in October.<ref name=":0" /> Gila monsters can live up to 40 years in captivity, though rarely.

Little is known about the social behavior of Gila monster, but it has been observed engaging in male to male combat, in which the dominant male lies on top of the subordinate one and pins it with its front and hind limbs. While fighting, both lizards arch their bodies, pushing against each other and twisting around in an effort to gain the dominant position. A "wrestling match" ends when the pressure exerts their forces, although bouts may be repeated.<ref name=":10"/> These bouts are typically observed in the mating season. Males with greater strength and endurance are thought to enjoy greater reproductive success.<ref name=":0" /> Although the Gila monster has a low metabolism and one of the lowest lizard sprint speeds, it has one of the highest aerobic scope values (the increase in oxygen consumption from rest to maximum metabolic exertion) among lizards, allowing it to engage in intense aerobic activity for a sustained period of time.

== Conservation status ==
Gila monsters are listed as [[near threatened]] by the [[IUCN]].<ref name="iucn status 19 November 2021" /> They are listed as "Apparently Secure" by [[NatureServe]].<ref>{{cite web |title=NatureServe Explorer 2.0 |url=https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.103164/Heloderma_suspectum |website=explorer.natureserve.org |access-date=4 April 2022}}</ref>

In 1952, the Gila monster became the first venomous animal to be given legal protection.<ref name=":9" /> They are now protected in all states of their distribution. International trade in the species is regulated under Appendix II of [[CITES]].

=== Relocation ===
"Possibly the greatest threat to the continued existence of helodermatids is the man-made destruction of their habitat as the land is developed for construction or to create more cultivable land."<ref>{{Cite journal|last=Repp|first=Roger A.|date=2017|title=A Monstrous Helloween Treat|journal=Bulletin of the Chicago Herpetological Society|volume=52|issue=2|pages=28–35}}</ref> Gila monsters found in these situations and relocated – with best intentions – up to {{cvt|1.2|km}} &nbsp;away, return to where they were found within 2 months and at great effort. This is up to five times the normal energy use than if they had not been removed, which uses up their energy stores unnecessarily. The same is true for animals relocated to appropriate habitats. Besides this, they also become more exposed to predators. Therefore, the process of simple relocation is "naïve" and potentially dangerous for both the relocated animals and existing populations and for the inhabitants of the region where the resettlement is taking place. If relocating the lizards further away, they might be totally disoriented, thus their survival is still very questionable. A more successful strategy would be, for example, if the new "settlers" were offered intensive education about this species (e.g., limited toxicity, lifestyle) with the aim of tolerating the reptile or even being proud of having this unique "roommate" in one's own neighborhood.<ref name=":9">{{Cite journal|author1=Sullivan, Brian K. |author2=Kwiatkowski, Matthew A. |author3=Schuett, Gordon W. |date=2004 |title=Translocation of urban Gila Monsters: a problematic conservation tool |journal=Biological Conservation |volume=117 |issue=3 |pages=235–242 |doi=10.1016/j.biocon.2003.07.002|bibcode=2004BCons.117..235S }}</ref>

In 1963, the [[San Diego Zoo]] became the first zoo to successfully breed Gila monsters in captivity.<ref name="sandiego">{{cite web |url=http://www.sandiegozoo.org/animalbytes/t-gila_monster.html |title=San Diego Zoo's Animal Bytes: Gila Monster |publisher=[[San Diego Zoo]] |access-date=2008-05-19 |archive-date=2008-05-27 |archive-url=https://web.archive.org/web/20080527024604/http://www.sandiegozoo.org/animalbytes/t-gila_monster.html |url-status=live }}</ref> In the last two decades, experienced breeders have shared their knowledge and expertise to give advice to other herpetologists on overcoming the difficulties in ''Heloderma'' reproduction under human care.<ref name=":4" /><ref name="Seward">{{cite book |author=Seward, Mark|title=Dr. Mark Seward's Gila monster Propagation: How To Breed Gila monsters in Captivity |publisher=Natural Selections Publishing|year=2002|isbn=0-9701395-0-0|pages=80}}</ref><ref>{{Cite book |author1=Eidenmüller, B |author2=Reisinger, M. |title=Beaded Lizards and Gila Monsters, Captive Care and Husbandry|publisher=Edition Chimaira|year=2011|isbn=978-3-89973-498-0 |location=Frankfurt am Main|pages=}}</ref>

== Relationship with humans ==
Though the Gila monster is venomous, it poses little threat to humans due to its sluggish nature. Nevertheless, it has a fearsome reputation and is often killed by humans. Myths that have formed about the Gila monster include that the animal's breath is toxic enough to kill humans, that it can spit venom like a [[spitting cobra]], that it can leap several feet in the air to attack,<ref name="sandiego" /> and that the Gila monster did not have an anus and therefore expelled waste from its mouth, the source of its venom and "fetid breath" (perhaps stemming from the fact that its venom in fact has an intense, specific smell).<ref name=":4" /> Among Native American tribes, the Gila monster has a varied reputation. The [[Apache]] believed its breath could kill a man, and the [[Tohono O'Odham]] and the [[Pima people|Pima]] believed it possessed a spiritual power that could cause sickness. In contrast, the [[Seri people|Seri]] and the [[Yaqui people|Yaqui]] believed the Gila monster's hide had healing properties. The Navajo/Dine believe the Gila monster was the first medicine man.

=== In popular culture ===
The Gila monster starred as a monster in the film ''[[The Giant Gila Monster]]'' (though the titular monster was actually portrayed by a Mexican beaded lizard).<ref>{{Cite web|date=2011-12-01|title=Gila Monsters And Beaded Lizards|url=https://www.reptilesmagazine.com/gila-monsters-and-beaded-lizards/|access-date=2021-01-08|website=Reptiles Magazine|language=en-US|archive-date=2020-11-12|archive-url=https://web.archive.org/web/20201112031358/https://www.reptilesmagazine.com/gila-monsters-and-beaded-lizards/|url-status=live}}</ref> It played a minor role in the motion picture ''[[The Treasure of the Sierra Madre (film)|The Treasure of the Sierra Madre]]''. In [[Brock Brower]]'s 1971 novel ''The Late Great Creature'', fictional [[horror movie]] star Simon Moro is presented as famous for playing the [[reptile|reptilian]] [[werewolf]]-like Gila Man. The 2011 animated film ''[[Rango (2011 film)|Rango]]'' featured a Gila monster as an Old West outlaw named Bad Bill, voiced by [[Ray Winstone]].<ref name="coyle">{{cite web |last=Coyle |first=Jake |url=http://www.northjersey.com/arts_entertainment/117402158_Movie_review___Rango_.html?page=all |title=Movie review: 'Rango' |publisher=Associated Press via NorthJersey.com |date=March 4, 2011 |archive-url=https://web.archive.org/web/20121001181724/http://www.northjersey.com/arts_entertainment/117402158_Movie_review___Rango_.html |archive-date=October 1, 2012 |url-status=dead }}</ref>

The Gila monster has also seen usage as a [[mascot]] and [[United States state symbols|state symbol]]. The official mascot of [[Eastern Arizona College]] located in [[Thatcher, Arizona]], is Gila Hank, a gun-toting, cowboy hat-wearing Gila monster.  In 2017, the [[Vegas Golden Knights]] selected a Gila monster named [[List of NHL mascots#Chance the Gila Monster|Chance]] as their official mascot.<ref>{{cite news|title=Vegas Golden Knights reveal Chance as team's mascot|url=https://www.reviewjournal.com/sports/golden-knights-nhl/vegas-golden-knights-reveal-chance-as-teams-mascot/|access-date=1 May 2018|work=Las Vegas Review-Journal|date=October 13, 2017|archive-date=15 October 2017|archive-url=https://web.archive.org/web/20171015045459/https://www.reviewjournal.com/sports/golden-knights-nhl/vegas-golden-knights-reveal-chance-as-teams-mascot/|url-status=live}}</ref> In 2019, the state of Utah made the Gila monster its official [[List of U.S. state reptiles|state reptile]].<ref>{{Cite web|url=https://le.utah.gov/~2019/bills/static/HB0144.html|title=HB0144|website=le.utah.gov|access-date=2019-05-15|archive-date=2019-03-29|archive-url=https://web.archive.org/web/20190329193449/https://le.utah.gov/~2019/bills/static/HB0144.html|url-status=live}}</ref>

In 2023, Australian band [[King Gizzard and the Lizard Wizard]] released a single titled "[[Gila Monster (song)|Gila Monster]]" from their album ''[[PetroDragonic Apocalypse]]'', with the album's artwork featuring a Gila monster on its cover art and heavily within the album's concept narrative.<ref>{{Cite web |last=Cohen |first=Jonathan |date=4 March 2023 |title=King Gizzard And The Lizard Wizard Unleash 'Gila Monster' In Wild New Video |url=https://www.spin.com/2023/05/king-gizzard-gila-monster-video/ |access-date=16 May 2023 |website=[[Spin (magazine)|Spin]]}}</ref>

== Gallery ==
<gallery mode="packed" heights="110">
File:Common Chuckwalla (Sauromalus ater), Giant Horned Lizard (Phrynosoma asio), Gila Monster (Heloderma suspectum).jpg|With a [[Sauromalus ater|common chuckwalla]] and a [[giant horned lizard]], [[Bronx Zoo]]
File:Gila monster - Animaux venimeux et venins, 1922 (18172980816).jpg|Illustration in ''Animaux venimeux et venins'', 1922
File:Terrarien-Gestaltung.jpg|alt=Tank setup with a hiding bowl|Tank setup with hiding bowl
File:Three-female-gila-monsters.jpg|alt=Pattern variations of female Helderma suspectum|Pattern variations of female ''H. suspectum''
File:Gila-monster-6-eggs.jpg|Egg deposit in captivity
File:Schluepfendes-jungtier-OS6.jpg|End of hatching process
File:Pralles-abdomen.jpg|Absorbed yolk in the abdomen
File:Group of young gila monster.jpg|Group of Gila monster hatchlings
File:Gila monster twins hatching.jpg|Gila monster twins hatching
</gallery>

== References ==
{{Reflist|colwidth=30em}}

== Further reading ==
* {{cite book |author=Beck, Daniel D. |title=Biology of Gila Monsters and Beaded Lizards |publisher=University of California Press |location=Berkeley |year=2005 |isbn=0-520-24357-9 }}
* {{cite book |last=Bogert |first=Charles M.|author2=Rafael Martin del Campo|title=The Gila Monster and its allies: the relationships, habits, and behavior of the lizards of the Family Helodermatidae|publisher=Bull. Amer. Mus. Natur. Hist. 109:1–238 |location=New York|year=1956 |pages=238}} [http://hdl.handle.net/2246/1232 Online .pdf]
* {{cite book|last= Capula|first= Massimo|author2= Behler|title= Simon & Schuster's Guide to Reptiles and Amphibians of the World|year= 1989|publisher= [[Simon & Schuster]]|location= [[New York City|New York]]|isbn= 0-671-69098-1|url= https://archive.org/details/simonschustersgu00capu}}
* {{cite book |author1=Carmony, Neil B. |author2=Brown, David |title=Gila Monster: Facts and Folklore of America's Aztec Lizard |publisher=High-Lonesome Books |location=Silver City, NM |year=1991 |isbn=0-944383-18-1 }}
* {{cite book  | last1 = Cogger  | first1 = Harold  | author-link = Harold Cogger  | last2 = Zweifel  | first2 = Richard  | title = Reptiles & Amphibians  | publisher = Weldon Owen  | location = [[Sydney, Australia]]  | year = 1992  | isbn = 0-8317-2786-1  | url = https://archive.org/details/reptilesamphibia00coggrich  }}
* {{cite book  | last =Ditmars  | first =Raymond L  | author-link =Raymond Ditmars  | title = Reptiles of the World: The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres  | publisher =Macmillan  | year =1933  | location =[[New York City|New York]]  | pages =321}}
* {{cite book|last1= Freiberg|first1= Dr. Marcos|last2= Walls|first2= Jerry|title= The World of Venomous Animals|year= 1984|publisher= TFH Publications|location= [[New Jersey]]|isbn= 0-87666-567-9|url= https://archive.org/details/worldofvenomousa00marc}}
* {{cite book |author1=Roever, J. M. |author2=Hiser, Iona Seibert |title=The Gila Monster |publisher=Steck-Vaughn Co |location=Austin, Tex |year=1972 |isbn=0-8114-7739-8 |url=https://archive.org/details/gilamonster00hise }}
* Schwandt, Hans-Joachim (2019). [https://www.heloderma.net/en/ heloderma.net] ''The Gila Monster Heloderma suspectum - Natural History, Husbandry & Propagation'', Edition Chimaira, Frankfurt/Main, {{ISBN|978-3-89973-441-6}}
*{{Cite book|last=Stebbins|first=Robert|title=Western Reptiles and Amphibians|publisher=Houghton Mifflin|year=2003|isbn=0-395-98272-3|location=New York}}
*{{Cite book|author1=Stephan F. K. Schaal |author2=Krister T. Smith |author3=Jörg Habersetzer |title=Messel – An Ancient Greenhouse Ecosystem|publisher=Senckenberg Forschungsinstitut|year=2018|isbn=978-3-510-61411-0|location=Frankfurt am Main}}

==External links==
*{{Wikispecies-inline|Heloderma suspectum}}
*{{Commons-inline}}

{{Varanoidea}}
{{Taxonbar|from=Q207058}}
{{Authority control}}

[[Category:Helodermatidae]]
[[Category:Reptiles described in 1869]]
[[Category:Venomous lizards]]
[[Category:Fauna of the Sonoran Desert]]
[[Category:Reptiles of Mexico]]
[[Category:Reptiles of the United States]]
[[Category:Fauna of the Southwestern United States]]
[[Category:Articles containing video clips]]
[[Category:Taxa named by Edward Drinker Cope]]
[[Category:Symbols of Utah]]
[[Category:Fauna of California]]