View source for Large blue

{{Short description|Species of butterfly}}
{{hatnote|"Large blue" can also refer to other species of ''[[Phengaris]]'' or the genus ''[[Lepidochrysops]]''.}}
{{Use British English|date=November 2016}}
{{Speciesbox
| status = NT
| status_system = IUCN2.3
| status_ref = <ref name=IUCN>{{Cite iucn | author = Gimenez Dixon, M. | title = ''Phengaris arion'' | volume = 1996 | article-number = e.T12659A3371159 | year = 1996 | doi = 10.2305/IUCN.UK.1996.RLTS.T12659A3371159.en | doi-access = free }}</ref>
| status2 = NT 
| status2_system = IUCN3.1
| status2_ref = <ref>{{cite iucn |author=van Swaay, C. |author2=Ellis, S. |author3=Warren, M. |year=2025 |title=''Phengaris arion'' (Europe assessment) |volume=2025 |article-number=e.T12659A211379800 |doi=10.2305/IUCN.UK.2025-1.RLTS.T12659A211379800.en |access-date=5 October 2025}}</ref>
| image = Maculinea arion Large Blue Upperside SFrance 2009-07-18.jpg
| image_caption = Upperside
| image2 = Maculinea arion Large Blue Underside SFrance 2009-07-18.jpg
| image2_caption = Underside
| genus = Phengaris
| species = arion
| authority = ([[Linnaeus, 1758]])
| synonyms = 
*''Papilio arion'' <small>Linnaeus, 1758</small>
*''Glaucopsyche arion'' <small>(Linnaeus, 1758)</small>
*''Maculinea arion'' <small>(Linnaeus, 1758)</small>
*''Nomiades arion''
| range_map = Maculinea arion distribution.png
| range_map_caption = 
}}

The '''Large blue''' ('''''Phengaris arion''''') is a species of butterfly in the family [[Lycaenidae]]. The species was first defined in 1758 and first recorded in [[Great Britain|Britain]] in 1795.<ref name=":14">{{cite web |last=Eeles |first=Peter |title=Large Blue |url=http://www.ukbutterflies.co.uk/species.php?species=arion |access-date=15 November 2013}}</ref> In 1979 the species became mostly extinct in Britain but has been successfully reintroduced with new conservation methods.<ref>{{cite web |title=Large Blue (''Phengaris'' (''Maculinea'') ''arion'') |url=http://www.ukbms.org/SpeciesFactsheets.aspx?speciesId=73 |access-date=15 November 2013 |archive-date=12 November 2017 |archive-url=https://web.archive.org/web/20171112132317/http://www.ukbms.org/SpeciesFactsheets.aspx?speciesId=73 }}</ref> The species is classified as "near threatened" on the [[IUCN Red List of Threatened Species]].<ref name=IUCN/> Today ''P. arion'' can be found in Europe, the [[Caucasus]], [[Armenia]], western [[Siberia]], Altai, north-western [[Kazakhstan]] and [[Sichuan]].<ref name=IUCN/>

The large blue can be distinguished by its unique speckled black dots on its wings with a blue background.

The large blue butterfly is well known in [[Behavioral ecology|behavioural ecology]] as it is a [[brood parasite]] of a single species of red ant, ''[[Myrmica sabuleti]]''.<ref name=":14"/> The discovery was made by Captain [[Edward Bagwell Purefoy]] along with [[Frederick William Frohawk|F. W. Frohawk]] and others.

== Subspecies ==
* ''P. a. arion'' Mainland Europe, western Siberia, Altai, north-western Kazakhstan 
* ''P. a. delphinatus'' <small>(Fruhstorfer, 1910)</small>
* ''P. a. zara'' <small>(Jachontov, 1935)</small> Caucasus, Armenia<ref>Butterfly Conservation Armenia</ref>
* ''P. a. buholzeri'' <small>(Rezbanyai, 1978)</small>
* {{extinct}} ''P. a. eutyphron'' <small>(Fruhstorfer, 1915)</small> formerly southern Britain

== Description ==
Large blue [[caterpillar]]s grow to about half an inch (13 millimetres) in length, and spend up to 9 months before they undergo [[metamorphosis]] to a [[Pupa#Chrysalis|chrysalis]] to become a [[butterfly]]. Large blue butterflies are one of the largest in the family [[Lycaenidae]], known as the gossamer-winged butterfly, with a wingspan of up to {{convert|2|in|mm|abbr=off}}, and live only for a few weeks. The wings of the large blue butterfly are speckled with black dots.{{citation needed|date=June 2022}}
<gallery mode=packed   heights="140px">
(MHNT) Phengaris arion - Radawa Poland - male dorsal.jpg |''Phengaris arion'' ♂  	
(MHNT) Phengaris arion - Radawa Poland - male ventral.jpg |''Phengaris arion'' ♂  △
Phengaris arion MHNT.CUT.2012.0357 col de Néal Arvieux - Gynadromorphe.jpg|[[Gynandromorph]]
</gallery>

== Description by Seitz ==
{{Main|Adalbert Seitz}}
{{Lepidopteran glossary hatnote}}
L. arion L. (83 c). Larger, above of a lighter and more shining blue [than ''arcas''], with a row of black spots across both wings, the spots being sometimes obsolete only on the hindwing of the male. At once recognized by the large number of ocelli on the underside, especially on the hindwing, and by the bright blue dusting of the base beneath. Europe and Anterior Asia, from North Europe, the Baltic provinces, and England to the Mediterranean (Corsica), and from Spain to Armenia and South Siberia. In ab. ''unicolor'' Hormuz. the upperside is entirely blue, all the black spots with the exception of the discocellular one being absent. ab. ''Arthurus'' Melvill is without ocelli beneath. In ab. ''jasilkowskii'' Hornuz the ocelli are absent beneath in the cell as in ''euphemus'', from which this aberration is at once distinguished by its blue-green basal scaling on the underside. In ab. ''coalescens'' Gillm. the black spots of the upperside are confluent. — Quite a number of local forms have been separated Northern specimens, which are feebly spotted, are named ''alconides'' by Aurivillius. — ''obscura'' Christ. (83 c) is an alpine form in which the whole outer half of the wings above is black or dark brown; it occurs typically in the High Alps, being locally very plentiful, e. g. at Bergun, Zermatt, Stilvio and at many places in the Alpes Maritimes. This darkened form occurs also in the Ural (= ''ruehli'' Krulik.) — In the South two aberrant forms have been found, namely ''ligurica'' Wagn., at the Eiviera between San Remo and Bordighera, with a conspicuous row of white marginal ocelli on the upperside of the hindwing, and ''aldrovandus'' S. L., from the Vesuvius, the underside darkened with brown. — ''cyanecula'' Stgr. [ now species ''[[Phengaris cyanecula]]'' (Eversmann, 1848)] (83 d) is an Asiatic form, from the Caucasus to Mongolia, with the metallic blue green dusting of the hindwing beneath being abundant, bright, and extending almost to the distal edge. — Egg very flat semiglobular, pale bluish white, deposited on ''Thymus'' which just begins to flower. Larva adult pale ochreous, with a pale lilac tinge at the sides; head ochreous, marked with black anteriorly; prothoracic plate black; feeds until the autumn on Thyme, then disappears and is found full grown the next June in the nests of ants. It is therefore suggested that the ants feed it up (Frohawk) and perhaps also protect the pupae. The chrysalis the colour of amber except for the wing-cases, smooth, somewhat elongate, without web. The butterflies occur usually singly, being locally frequent on open ground, on broad roads through shrubby woods, flying about 1 m above the ground. They rest with closed wings, particularly on Thymes and Scabious. On the wing from the end of June into August.<ref>[[Adalbert Seitz]] ''Die Großschmetterlinge der Erde'', Verlag Alfred Kernen, Stuttgart Band 1: Abt. 1, Die Großschmetterlinge des palaearktischen Faunengebietes, Die palaearktischen Tagfalter, 1909, 379 Seiten, mit 89 kolorierten Tafeln (3470 Figuren){{PD-notice}}</ref>

== Distribution ==
The large blue butterfly is found from coast to coast of the [[Palearctic realm]], but is most concentrated in the areas from [[France]] to [[China]].<ref name=":12">{{cite journal |last=Muggleton |first=John |author2=Brian Benham |title=Isolation and the decline of the large blue butterfly (Maculinea arion) in Great Britain |journal=Biological Conservation |year=1975 |volume=7 |issue=2 |pages=119–128 |doi=10.1016/0006-3207(75)90051-8|bibcode=1975BCons...7..119M }}</ref><ref name=":4">{{cite journal |last=Wynhoff |first=Irma |title=The recent distribution of the European Maculinea species |journal=Journal of Insect Conservation |year=1998 |volume=2 |pages=15–27|doi=10.1023/A:1009636605309|s2cid=27089897 }}</ref>

=== Habitat ===
[[File:Pengannel - Large Blue (by).jpg|thumb|A large blue on ''[[Thymus praecox]]'']]
[[File:Phengaris arion (Common Blue) grooming, taking flight.webm|thumb|A large blue on food plant, grooming itself and taking to the air. Underside of wings shown plus partial reveal of upperside.]]

The habitat of the large blue butterfly is largely influenced by location of its food sources. The species requires a combination of abundant amounts of its larval food plant, ''[[Thymus (plant)|Thymus drucei]]'' and the presence of ''[[Myrmica sabuleti]]'' ants in order to survive.<ref name=":12" />

It has also been found that an underlying key factor for the survival of the large blue is site [[heterogeneity]]. The butterfly is most abundant in pastures and abandoned areas of diverse vegetation and shrubbery.<ref name=":5" /> This preference can be explained by examining the result of a uniform landscape. A constant landscape synchronizes many biological activities including flowering of host plants, adult emergence dates, or larval pressures on the ant colonies.<ref name=":5">{{cite journal |last=Spitzer |first=L. |author2=J. Benes |author3=J. Dandova |author4=V. Jaskova |author5=M. Konvicka |title=The Large Blue butterfly, Phengaris [Maculinea] arion, as a conservation umbrella on a landscape scale: The case of the Czech Carpathians |journal=Ecological Indicators |year=2009 |volume=9 |issue=6 |pages=1056–1063 |doi=10.1016/j.ecolind.2008.12.006|bibcode=2009EcInd...9.1056S}}</ref> If important biological functions take place at the same times, the population becomes much more susceptible to random unfortunate events such as environmental disasters.<ref>{{cite book |last=Hanski |first=L. |title=Metapopulation Ecology |year=1999 |publisher=Oxford University Press |location=Oxford}}</ref> Thus traditional farming acts to desynchronize the biological system, and allows for re-colonization of patches that are temporarily untouched.<ref name=":5" /> The presence of differing sites and varied ecological structures provides differing [[microclimates]] that can make a huge impact on the survival of the large blue butterfly.<ref>{{cite journal |last=Davies |first=Z.G. |author2=R.J. Wilson |author3=S. Coles |author4=C.D. Thomas |title=Changing habitat associations of a thermally constrained species, the silver-spotted skipper butterfly, in response to climate warming |journal=Journal of Animal Ecology |year=2006 |volume=75 |issue=1 |pages=247–256 |doi=10.1111/j.1365-2656.2006.01044.x|pmid=16903062 |url=https://kar.kent.ac.uk/28305/1/Davies_et_al._JAE_2006.pdf |doi-access=free |bibcode=2006JAnEc..75..247D }}</ref>

=== Extinction/conservation ===
In the late 1900s, ''[[Phengaris]]'' populations began decreasing drastically throughout Europe with the large blue butterfly being particularly affected. By the 1950s, only an estimated 100,000 adults remained in Britain, and by 1978, 48% of the UK's 91 known large blue populations had been lost.<ref name=":6">{{cite journal |last=Thomas |first=J.A. |title=Why did the large blue become extinct in Britain? |journal=Oryx |year=1980 |volume=15 |issue=3 |pages=243–247 |doi=10.1017/s0030605300024625 |s2cid=86103291 |doi-access=free}}</ref><ref name=":7">{{cite book |last=Thomas |first=J.A. |title=Ecology and Conservation of Butterflies |chapter=The ecology and conservation of Maculinea arion and other European species of large blue butterfly |year=1995 |pages=180–197 |doi=10.1007/978-94-011-1282-6_13 |isbn=978-94-010-4559-9}}</ref> Initially experts were completely baffled by the disappearance of large blues as the sites did not appear to have changed.<ref name=":6" /> Leading hypotheses targeted collectors, [[insecticides]], and air pollution as factors that led to the butterfly extinction.<ref name=":7" /> A large number of projects were conducted to combat these factors, but all were completely unsuccessful.<ref name=":7" /> The species became extinct in the [[Netherlands]] in 1964, in the UK in 1979. In [[Belgium]], it had been considered extinct until 1996, when a recolonized population was discovered in the south of the country.<ref name=":4" /> Severe decreases in population have also occurred in [[Denmark]], [[Germany]], [[France]], and [[Estonia]].<ref name=":4" /> Because of this decline they are being protected. The succession of extinctions and decreases in population has been characterized as a result of unsuccessful conservation efforts that stemmed from a lack of understanding of the behaviour of the butterfly.<ref name=":6" /><ref>{{cite book |last=Thomas |first=J.A. |title=Rare species conservation: case studies of European Butterflies |year=1991 |publisher=Blackwell Scientific Publication |location=Oxford}}</ref>

Currently the large blue butterfly is classified as critically endangered in Britain as well as being endangered in many areas of Europe.<ref>{{cite journal |last=Fox |first=R. |author2=M.S. Warren |author3=T.M. Brereton |author4=D.B. Roy |author5=A. Robinson |title=A new red list of British butterflies |journal=Insect Conservation and Diversity |year=2011 |volume=4 |issue=3 |doi=10.1111/j.1752-4598.2010.00117.x |pages=159–172 |citeseerx=10.1.1.532.6784 |s2cid=86056452}}</ref> It is a priority species of under the [[UK Biodiversity Action Plan]].<ref>{{cite journal |last=Guillem |first=R.M. |title=Corrigendum to "Using chemo-taxonomy of host ants to help conserve the large blue butterfly" |journal=Biol. Conserv. |year=2012 |volume=148 |pages=39–43 |doi=10.1016/j.biocon.2012.01.066}}</ref> However, a long-term conservation project in the UK, led by the Royal Entomological Society, led to a significant increase in numbers in 2022, with the species described as "thriving".<ref>{{cite news |publisher=BBC News |date=26 August 2022 |author=Georgina Rannard |title=Huge recovery for butterfly once extinct in the UK |url=https://www.bbc.co.uk/news/science-environment-62674800 |access-date=26 August 2022}}</ref>

Recent findings have also shown that there is a positive correlation between large blue butterfly conservation success and that of other endangered species. One specific example is the relationship between ''Myrmica'' ants, the large blue butterfly, violet seeds, and the violet-feeding butterfly (''[[Boloria euphrosyne]]'').<ref>{{cite book |last=Randle |first=Z. |title=Studies on the ecology and conservation of butterflies in Europe. Species ecology along a European gradient: Maculinea butterflies as a model |author2=D.J. Simcox |author3=K. Schronrogge |author4=J.C. Wardlaw |author5=J.A. Thomas |publisher=Pensoft |year=2005 |editor-last=Settele |editor-first=J. |volume=2 |chapter=Myrmica ants as keystone species and Maculinea arionas an indicator of rare niches in UK grasslands |editor-last2=Kühn |editor-first2=E. |editor-last3=Thomas |editor-first3=J.A.}}</ref> The ants will bring the violet seeds into the nest. The seeds will often germinate in the nest, and their potential for germination increases as the nest becomes deserted.<ref name=":5" /> Since large blue butterfly predation of ant larvae can lead to desertion of the nest and ''B. euphrosyne'' tend to prefer violets growing on deserted ant nests, the fitness of ''B. euphrosyne'' appears to be indirectly affected by the presence of the large blue.<ref name=":5" />

==Behaviour==
===Brood parasitism===
{{further|Brood parasite}}

Like many members of the genus ''[[Phengaris]]'', large blues are [[brood parasite]]s, relying on another insect to raise their young. In this case, the hosts are species of ''[[Myrmica]]'' ant.<ref>{{cite journal |last=Sielezniew |first=Marcin |author2=Dario Patricelli |author3=Izabela Dziekańska |author4=Francesca Barbero |author5=Simona Bonelli |author6=Luca Pietro Casacci |author7=Magdalena Witek |author8=Emilio Balletto |name-list-style=amp |title=The First Record of Myrmica lonae (Hymenoptera: Formicidae) as a Host of the Socially Parasitic Large Blue Butterfly Phengaris (Maculinea)* arion (Lepidoptera: Lycaenidae) |journal=Sociobiology |year=2010 |volume=56 |pages=465–475}}</ref> By being physically and chemically similar to ''Myrmica'' ants in their larval stage, and possibly by using other forms of mimicry, ''Phengaris'' caterpillars trick the ants into taking them back to the ant nest.<ref name=":0">{{cite journal |last=Thomas |first=Jeremy |author2=Karsten Schönrogge |author3=Simona Bonelli |author4=Francesca Barbero |author5=Emilio Balletto |title=Corruption of ant acoustical signals by mimetic social parasites |journal=Communicative and Integrative Biology |year=2010 |volume=3 |issue=2 |pages=169–171 |doi=10.4161/cib.3.2.10603 |pmid=20585513 |pmc=2889977}}</ref> Once there, the caterpillar will either become a predator of the ant larvae, or beg for food by acting like an ant larva in what is known as a "[[cuckoo]]" strategy.<ref>{{cite journal |last=Pech |first=Pavel |author2=Zdenek Fric |author3=Martin Konvicka |author4=Jan Zrzavy |title=Phylogeny of Maculinea blues (Lepidoptera: Lycaenidae) based on morphological and ecological characters: evolution of parasitic myrmecophily |journal=Cladistics |year=2004 |volume=20 |issue=4 |pages=362–375 |doi=10.1111/j.1096-0031.2004.00031.x |pmid=34892942 |citeseerx=10.1.1.716.2924 |s2cid=55777107}}</ref> The "cuckoo" method is viewed as a more successful strategy, as studies have consistently found more larvae per nest for cuckoo butterfly species than predator butterflies.<ref name=":1">{{cite journal |last=Witek |first=Magdalena |author2=EWA B. ĝLIWIēSKA |author3=PIOTR SKÓRKA |author4=PIOTR NOWICKI |author5=MARTA WANTUCH |author6=VLADIMÍR VRABEC |author7=JOSEF SETTELE |author8=MICHAL WOYCIECHOWSKI |display-authors=3 |title=Host ant specificity of large blue butterflies Phengaris (Maculinea) (Lepidoptera: Lycaenidae) inhabiting humid grasslands in East-central Europe |journal=European Journal of Entomology |year=2008 |volume=105 |issue=5 |pages=871–877 |doi=10.14411/eje.2008.115 |doi-access=free}}</ref><ref name=":3">{{cite journal |last=Sielezniew |first=Marcin |author2=Anna M. Stankiewicz |title=Myrmica sabuleti (Hymenoptera: Formicidae) not necessary for the survival of the population of Phengaris (Maculinea) arion (Lepidoptera: Lycaenidae) in eastern Poland: Lower host-ant specificity or evidence for geographical variation of an endangered social parasite? |journal=European Journal of Entomology |year=2008 |volume=105 |issue=4 |pages=637–641 |doi=10.14411/eje.2008.086 |url=http://www.eje.cz/doi/10.14411/eje.2008.086.pdf |doi-access=free}}</ref><ref>{{cite journal |last=Als |first=Thomas |author2=Roger Vila |author3=Nikolai P. Kandul |author4=David R. Nash |author5=Shen-Horn Yen |author6=Yu-Feng Hsu |author7=André A. Mignault |author8=Jacobus J. Boomsma |author9=Naomi E. Pierce |title=The evolution of alternative parasitic life histories in large blue butterflies |journal=Nature |year=2004 |volume=432 |issue=7015 |pages=386–390 |doi=10.1038/nature03020 |pmid=15549104 |bibcode=2004Natur.432..386A |s2cid=4357717 }}</ref> Through much research, it has been well documented that large blue butterflies act as predators in the host nests.

==== Host species ====
Early ideas of the ''Phengaris-Myrmica'' relationship resulted in the construction of a linear relationship between one predator and one host. It was proposed that each species of ''Phengaris'' had evolutionarily adapted to prey on one specific species of ''Myrmica'' with the large blue focusing on ''M. sabuleti''.<ref name=":1" /> More recent reports indicate that while each ''Phengaris'' species can prey on more than one ''Myrmica'' species, that ability varies between species and each butterfly species still prefers a specific ant species.<ref name=":1" /> The large blue has also been documented to prey on ''[[Myrmica scabrinodis|M. scabrinodis]]''.<ref name=":3" /> Additional studies have also shown that the large blue may exhibit different host preferences depending on location. For example, in Finland, large blue butterflies exclusively fed off ''[[Myrmica lonae|M. lonae]]'' nests<ref name=":3" /> and in Poland they were found in the nests of ''[[Myrmica rugulosa|M. rugulosa]]'', ''[[Myrmica hellenica|M. hellenica]]'', and ''[[Myrmica schencki|M. schencki]]''.<ref name=":3" />

==== Egg laying ====
Since the parasitic-host relationship between the large blue and the ''Myrmica'' is essential for the caterpillar survival, female butterflies must lay eggs in areas where the larvae can be found by ant workers of the correct species. In the past it was unclear if ''Phengaris'' butterflies were capable of identifying areas of specific ''Myrmica'' species. It was believed that the certain species of ''Phengaris'' could detect specific odours to identify ''Myrmica'' species.<ref name=":2">{{cite journal |last=Thomas |first=J.A. |author2=G.W. Elmes |title=Food–plant niche selection rather than the presence of ant nests explains oviposition patterns in the myrmecophilous butterfly genus Maculinea |journal=Proc. R. Soc. Lond. B |year=2001 |volume=268 |issue=1466 |pages=471–477 |doi=10.1098/rspb.2000.1398 |pmid=11296858 |pmc=1088629}}</ref> It was also thought that certain species of ''Phengaris'' were capable of avoiding overcrowding on food plants by detecting high egg loads.<ref name=":2" /> New studies indicate that female egg laying is merely attuned to the ''Myrmica'' species, and that females do not take other factors into consideration.<ref name=":1" /> Female ''Phengaris'' lay eggs on specific plants such as [[Thymus (plant)|thyme]].<ref>{{cite journal |last=Thomas |first=J.A. |author2=D.J. Simcox |author3=J.C. Wardlaw |author4=G.W. Elmes |author5=M.E. Hochberg |author6=R.T. Clarke |year=1997 |title=Effects of latitude, altitude and climate on the habitat and conservation of the endangered butterfly Maculinea arion and its Myrmica ant hosts |journal=Journal of Insect Conservation |volume=2 |pages=39–46 |doi=10.1023/A:1009640706218 |s2cid=23953195}}</ref> Wild thyme is the preferred food plant in the UK and in cooler or more mountainous areas in Europe, marjoram is preferred by populations in warmer areas.{{Citation needed|date=July 2025}}

==== Larva/caterpillar stage ====
After about three weeks, larvae hatch to feed on the seeds and flowers of the plant. The caterpillar will stay in the vicinity of its food plant until its 4th [[instar]], when it will drop to the ground.<ref name=":1" /> From there the caterpillar will adopt various strategies to be found by ''Myrmica'' ants. Large blue caterpillars will sometimes follow ant trails or move away from the food plant during peak-foraging time to expose themselves specifically to ''Myrmica'' and not other ants.<ref>{{cite journal |last=Thomas |first=J. |year=2002 |title=Larval niche selection and evening exposure enhance adoption of a predacious social parasite, Maculinea arion (large blue butterfly), by Myrmica ants |journal=Oecologia |volume=132 |issue=4 |pages=531–537 |bibcode=2002Oecol.132..531T |doi=10.1007/s00442-002-1002-9 |pmid=28547639 |s2cid=20604417}}</ref> Several caterpillar species of ''Phengaris'', such as ''[[Phengaris rebeli|P. rebeli]]'' and ''[[Phengaris alcon|P. alcon]]'', will secrete pheromones that are specific to their respective hosts. The purpose of such behaviour is to mimic the pheromones of ant larvae that will become workers in the future.<ref name="Thomas queen ants">{{cite journal |last=Thomas |first=J.A. |author2=J.C. Wardlaw |title=The effect of queen ants on the survival of Maculinea arion larvae in Myrmica ant nests |journal=Oecologia |year=1990 |volume=85 |issue=1 |pages=87–91 |doi=10.1007/bf00317347 |pmid=28310959 |bibcode=1990Oecol..85...87T |s2cid=32623923}}</ref> By successfully mimicking ant larvae, the caterpillars are taken back to the host nest and fed by the ants. Originally it was thought that the large blue butterfly behaved differently in that some believed it either secreted a poor pheromone mimic, or did not secrete one at all.<ref name="Thomas queen ants" /> This was inferred from the fact that worker ants tended to neglect the caterpillars once in the nest.<ref name="Thomas queen ants" /> Today it has been determined that it still secretes [[semiochemical]]s as a form of [[chemical mimicry]] to gain acceptance into the host ant nest.<ref name=":0" />

==== Behaviour in the host nest ====
===== "Cuckoo" strategy =====
While most ''Phengaris'' caterpillars behave similarly before entering the host ant nest, once adopted into a nest the larvae adopt one of two strategies. The first is the [[brood parasite|"cuckoo" strategy]]. This has been studied extensively in ''[[Phengaris rebeli|P. rebeli]]'', and consists of continued interaction between the caterpillar and the host ants. Once in the nest, the caterpillar uses acoustic [[mimicry]] to hide its identity.<ref>{{cite journal |last=DeVries |first=P.J. |author2=R.B. Cocroft |author3=J.A. Thomas |title=Comparison of acoustical signals in Maculinea butterfly caterpillars and their obligate host Myrmica ants |journal=Biol. J. Linn. Soc. |year=1993 |volume=49 |issue=3 |pages=229–238 |doi=10.1006/bijl.1993.1033 |bibcode=1993BJLS...49..229D}}</ref> The large blue larvae using the cuckoo strategy stay in close quarters with the ants while producing a noise very similar to that of a larval [[queen ant]].<ref>{{cite journal |last=Cobb |first=Matthew |title=Caterpillars make noises like ants |journal=J. Exp. Biol. |year=2009 |volume=212 |issue=12 |page=v |doi=10.1242/jeb.021741 |doi-access=free |bibcode=2009JExpB.212R...5C}}</ref> By mimicking a queen, larva are fed by the worker ants and are given preferential treatment over the real ant larvae.<ref name=":8">{{cite journal |last=Settele |first=Josef |author2=Francesca Barbero |author3=Martin Musche |author4=Jeremy A. Thomas |author5=Karsten Schönrogge |title=Singing the blues: from experimental biology to conservation application |journal=J. Exp. Biol. |year=2011 |volume=214 |issue=9 |pages=1407–1410 |doi=10.1242/jeb.035329 |pmid=21490248 |bibcode=2011JExpB.214.1407S}}</ref> Cuckoo strategy users become such high-status members of the nest that the ants will kill their own larvae to feed the caterpillar and will rescue the caterpillar first in the face of danger.<ref name=":8" />

===== Predator strategy =====
Unlike other members of the genus ''Phengaris'', the large blue becomes a predator once in the ant nest. It feeds on the ant pupae while continuing to pose as a ''Myrmica'' ant. Even with mimicry, mortality for the large blue within the nest is high.<ref name="Thomas queen ants" /> One explanation is that each species of ''Phengaris'' is most suited for a single species of ''Myrmica''. Caterpillars that are adopted by an unfamiliar species of ant are often killed and eaten.{{Citation needed|date=July 2025}} Even if matched with the correct host, many large blue butterflies are unable to survive. If the mimicry is not perfect and the ants become suspicious, death is highly likely.<ref name="Thomas queen ants" /> Further, ants in nests without a consistent supply of food are much more likely to identify the large blue as an intruder.<ref name="Thomas queen ants" /> Large blue caterpillars are most likely to be attacked during the first 10 days after being adopted by the host ants.<ref name="Thomas queen ants" /> This is because in this time the caterpillars become larger than typical ''Myrmica'' ant larvae.<!--eh? Then they'll be even larger later!--><ref name="Thomas queen ants" />

===== Mimicry =====
Even once ''Phengaris'' butterflies have infiltrated the host nest, they continue to hide their identity as caterpillars and will go further in their act of deception. There have been many studies documenting the use of acoustic communication in ants, and it has been found that members of the genus ''Phengaris'' exploit this behaviour. For example, ''P. rebeli'' mimics the unique sound of the queen to elevate its status in the nest. This mimicry is effective enough to cause worker ants to prefer to rescue the ''P. rebeli'' over their own pupae in times of danger.<ref name=":9">{{cite journal |last1=Barbero |first1=F. |last2=Thomas |first2=J. A. |last3=Bonelli |first3=S. |last4=Balletto |first4=E. |last5=Schonrogge |first5=K. |title=Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite |journal=Science |volume=323 |issue=5915 |year=2009 |pages=782–785 |doi=10.1126/science.1163583 |pmid=19197065 |bibcode=2009Sci...323..782B |s2cid=206515276}}</ref>

Previously it had been thought that only "cuckoo" strategy species used acoustic mimicry.<ref name=":0" /> The sound was so similar, that the sounds of the two caterpillars differed more than each did compared to the sound of the queen. Different ''Myrmica'' species utilize distinct semiochemicals to distinguish themselves, but they use very similar acoustic commands once in the nest.<ref name=":0" />

===== Lab studies and applications =====
Laboratory studies have shown that large blue butterfly larvae first consume the largest ant larvae. This evolved tactic maximizes efficiency not only because the largest larvae provide the most substance by volume, but also because it prevents the larvae pupating and becoming inaccessible prey. Further, it allows more newly hatched larvae time to grow bigger. While in the nest, large blue caterpillars acquire 99% of their final biomass, growing from an average of 1.3 mg to 173 mg. Results from laboratories estimate that 230 large larvae and a minimum of 354 ''Myrmica'' workers are needed to ensure the survival of one butterfly; however, such a large nest is very rarely found in the wild. This supports findings that large blue butterflies are extremely capable of withstanding starvation. This becomes extremely beneficial in situations when the ants desert the colony and leave the caterpillar behind. Large blue butterflies have been known to be capable of migrating to new nests once the original is deserted. In many cases, a nearby colony with a fresh brood will populate the nest allowing the surviving large blues to sequentially parasitize multiple ''Myrmica'' colonies.<ref name=":10">{{cite journal |last=Thomas |first=J.A. |title=The capacity of a Myrmica ant nest to support a predacious species of Maculinea butterfly |journal=Oecologia |year=1992 |volume=91 |issue=1 |pages=101–109 |doi=10.1007/BF00317247 |pmid=28313380 |bibcode=1992Oecol..91..101T |s2cid=35810639}}</ref>

===== Cuckoo vs. predatory strategies =====
Scientists remain unsure why there are multiple strategies within the host nest, but studies have been conducted to determine the effectiveness of each. The cuckoo strategy results in six times more butterflies per nest than the predatory strategy.<ref name=":11">{{cite journal |last=Thomas |first=Jeremy |author2=Josef Settele |title=Evolutionary biology: Butterfly mimics of ants |journal=Nature |year=2004 |volume=432 |issue=7015 |pages=283–284 |doi=10.1038/432283a |bibcode=2004Natur.432..283T |pmid=15549080 |s2cid=4379000 |doi-access=free}}</ref> While this seems to indicate a dominance of the cuckoo strategy, there are other factors to consider. Since the cuckoo caterpillars remain in close vicinity of the ants, they must secrete chemicals that are almost identical to the host species in order to survive.<ref name=":11" /> This explains why cuckoo strategy users are more likely to be predated by the host colony when adopted by a non-primary host than predatory strategy users.<ref name=":9" /> Current data seem to support the idea that cuckoo strategy users depend on a specific species of ''Myrmica'' ant while predatory ''Phengaris'' are more versatile overall but still perform better with a specific species.<ref name=":11" />

===== The queen effect =====
It has been found that large blue butterflies are three times less likely to survive in nests that have queen ants present. This discovery has been explained with a theory called the "queen effect". In most ''[[Myrmica]]'' nests, the queen ant will lay two main batches of eggs, and the females that hatch from these eggs will either become workers or [[Queen ant|virgin queens]]. Whether these females become workers or virgin queens is dependent on the status of the queen in the nest. If the queen dies, worker ants have the largest of the female larvae transition into virgin queens. If the queen is present and healthy, she influences the nurse workers to neglect, starve and bite the female larvae which results in restricted growth and aids in the transition to workers.<ref name="Thomas queen ants" /> This indicates that ''Phengaris'' butterflies must maintain a strict balance between mimicking the queen in the presence of workers and appearing to be a worker to avoid the queen.

== See also ==
* [[List of butterflies of Great Britain]]

== References ==
{{Reflist}}

==External links==
{{Commons}}
{{Wikispecies|Phengaris arion}}
* [http://www.zi.ku.dk/personal/drnash/atta/Pages/LargeBl.html Life cycle]
* [http://butterfly-conservation.org/4494/expanding-the-large-blue-landscape-in-the-polden-hills.html Butterfly Conservation - large blue project]
* [https://web.archive.org/web/20160817084031/http://www.cornwallwildlifetrust.org.uk/species/large-blue Cornwall Wildlife Trust - large blue reintroduction]

{{Brood parasite}}
{{Taxonbar|from=Q161528}}

[[Category:Phengaris]]
[[Category:Butterflies of Africa]]
[[Category:Butterflies of Asia]]
[[Category:Butterflies of Europe]]
[[Category:Butterflies of Japan]]
[[Category:Butterflies described in 1758]]
[[Category:Animal taxa named by Carl Linnaeus]]
[[Category:Near threatened animals]]
[[Category:Near threatened biota of Asia]]
[[Category:Articles containing video clips]]
[[Category:Brood parasites]]