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 Britain in 1795. In 1979 the species became mostly extinct in Britain but has been successfully reintroduced with new conservation methods. The species is classified as "near threatened" on the IUCN Red List of Threatened Species.
- P. a. buholzeri <small>(Rezbanyai, 1978)</small>
- P. a. eutyphron <small>(Fruhstorfer, 1915)</small> formerly southern Britain
Description
Large blue caterpillars grow to about half an inch (13 millimetres) in length, and spend up to 9 months before they undergo metamorphosis to a 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 , and live only for a few weeks. The wings of the large blue butterfly are speckled with black dots.
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(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
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Description by Seitz
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.
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.
Habitat
thumb|A large blue on [[Thymus praecox]]
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 drucei and the presence of Myrmica sabuleti ants in order to survive. If important biological functions take place at the same times, the population becomes much more susceptible to random unfortunate events such as environmental disasters. Thus traditional farming acts to desynchronize the biological system, and allows for re-colonization of patches that are temporarily untouched.
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. Initially experts were completely baffled by the disappearance of large blues as the sites did not appear to have changed.
Currently the large blue butterfly is classified as critically endangered in Britain as well as being endangered in many areas of Europe. It is a priority species of under the UK Biodiversity Action Plan. 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".
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). 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. 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. 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. 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. 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. It was also thought that certain species of Phengaris were capable of avoiding overcrowding on food plants by detecting high egg loads. 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.
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. Several caterpillar species of Phengaris, such as P. rebeli and 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. 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. 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. By mimicking a queen, larva are fed by the worker ants and are given preferential treatment over the real ant larvae. 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.
Previously it had been thought that only "cuckoo" strategy species used acoustic mimicry.
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. 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.