Silver-studded blue

L. argus L. ([equals] aegon Schiff., argyrotoxus Bgstr.) (78 c). This and the following species [argyrognomon] have in the anal area of the hindwing beneath on the black submarginal dots situated between the median branches and the submedian vein some metallic glittering scales which are usually not represented in our figures. The upperside is deep dark blue, with a broad black border, argus is very similar to argyrognomon, but differs in quite a number of details, of which in the various individuals sometimes one sometimes another is more conspicuously developed. On the upperside the blue gloss is deeper, darker, duller, with a slight violet tint and not so far extended to the margin, the latter being broader and appearing blacker; the row of dark submarginal dots which occasionally appear on the hindwing above in both species, therefore stands always in the black border in argus. On the underside both sexes of argus have nearly always a strongly glittering blue-green dusting at the base of the wings, which is usually absent from argyrognomon; but we must add that also the inverse occurs, the blue basal dusting being absent from argus in exceptional cases and strongly marked in argyrognomon. As a rule argus L., moreover, is somewhat smaller than argyrognomon, but the size varies considerably according to the altitude of the locality and the various broods.

— ab. valesiana M.-Durr is frequently found among specimens from the Valais (but not exclusively and not constantly); it is distinguished by a yellowish grey underside and very small ocelli. ab. corsica Bell., on the other hand, is a form which flies regularly in the mountains of Corsica and differs in the ocelli of the underside bearing pupils of the ground-colour and having larger borders, which almost form pale rings on a grey-brown ground. This form occurs as an exception everywhere, having been obtained by Standen even in Norway. Females which are nearly as blue above as the males are not very rare in certain localities, especially among the summer-broad, this is ab. coerulescens Peters ([equals] pseudocallarga Neustetter).

— A constant form is hypochiona Rbr. (78 d, ground-colour too dull), from the most southern very sunny districts of Europe (Ionian Islands, Greece, Andalusia); underside rather pale, the black eye-dots small and placed in large pale halos, before the margin a row of bright red spots. Similar individuals are occasionally also found in other districts, e. g. at Digne and according to Jones even in England.

— A very large form is insularis Leech (78 d), from the north-island of Japan; its underside resembles hypochiona in its light pure ground-colour, but bears abundant and prominent black spots. Above the marginal spots of the hindwing are especially very distinct.

— Also bella H.-Sch. (78 d, e) is placed by Staudinger and Rebel as a variety of argus; it is a small form, which resembles hypochiona beneath, but is very dark above, with very thin red-yellow submarginal spots on the upperside of the hindwing, which are unfortunately not visible in our figure 78 d, the hindwing beneath bearing paler marginal spots; from the shores of the Black Sea, Armenia and Persia.

— Perhaps also iburiensis Btlr. [ now full species Plebejus iburiensis (Butler, [1882])]belongs here; it is unknown to me in nature and was described from one specimen from Hokkaido; it appears to be a kind of albino of insularis.

— Very small specimens, as they are found especially in Valais, are alpina Berce; exceptionally large specimens were obtained by Chapman at Bejar in Spain and named by him bejarensis [now subspecies].

— The form micrargus Btlr. [now subspecies] from Tokio, which is quite unknown to me, is said to have the lilac colour of argia, with the black margin dentate and the fringes very bright white; beneath in colour like pylaon, the spots as in argus, but without the metallic scales on the anal spots.

— pseudaegon Btlr. [now full species Plebejus pseudaegon (Butler, [1882])], from the north-island, is smaller than argus, with the black margin narrower, the white fringes thinner, and the black distal marginal spots of the hindwing above smaller, female very feebly dusted with steel-blue at the base, underside more extended green than in true argus and its ocelli smaller. Likewise unknown to me.

— Sometimes there occurs a basal dot on the underside; this is ab. unipuncta Mousley. In ab. coeruleocuneata Ebert there appear blue wedge-shaped submarginal spots on the upperside of the hindwing.

— Larva very variable, usually light green with dark dorsal spots, sometimes however grey or dark brown with pale spots. In June and the autumn on various plants, such as Coronilla, Trifolium, Colutea, and Genista, said to occur also on Erica, Ornithopus, Fragaria, Thymus and other plants. Near or upon the larva there is a guard of ants, usually specimens of Formica cinerea Mayr. The larva as well as the chrysalis are found in the nests of this ant. Pupa elongate, green with red dorsal line; abdomen above yellowish green. The butterflies are on the wing in May and again from July onwards, but are said to have only one brood in the north. They are common everywhere, especially on sandy soil, which also its ant prefers, but is said to noticeably decrease recently in numbers in some districts (e. g. in England). The form alpina I found in large numbers in Valais below Zermatt towards evening in stony localities where they were at rest in small bushes; I counted 38 sleeping specimens in a small thornbush, all having the small size of the form of that neighbourhood.[7]

Figs 3 larva before last moult, 3a larva after last moult, 3b pupa

P. argus is found across the Palearctic.[5] In the United Kingdom, the butterfly experienced a severe decline in population during the nineteenth and twentieth centuries.[1] P. argus is generally considered to be endangered and extinct in the Northern United Kingdom and are primarily found in the Southern and Western portions of the United Kingdom.[1]

P. argus resides in heathland, mossland, and limestone grassland.[5]

Heathlands are able to meet the needs of P. argus due to burning, cutting, and other disruptions of mature heaths.[9][5] With these disruptions, the habitat becomes conducive to habitation by P. argus because of the high cover of E. cinerea and short C. vulgaris that is able to form a landscape with the patches of bare ground. This is characteristic of heathland at an early stage of development.[1][9] This environment is suitable until the point at which the shrubs native to the environment mature and obscure the bare ground and vegetation margins that the butterflies use for oviposition.

Mossland, similar in nature to wet heathland, has soil primarily composed of peat which supports one of the families of host plants of P. argus, Ericaceae. This host plant grows alongside other grasses, sedges, and rushes. While the main disturbance to heathland is quarrying, mossland faces peat digging which contributes to the transient and shifting nature of this particular habitat.[5]

The hostplants of the first two environments, Ericaceae and Leguminosae, are less present in the third environment, limestone grassland.[9] In this environment, the host plants of P. argus are primarily herbaceous Cistaceae as well as Leguminosae.[9] In limestone grassland, the bare ground and vegetation margins instrumental to the life cycle of P. argus are created through grazing by other animals as well as by disruption of the habitat by natural disturbance of the stoney topography of this environment.

P. argus use shrubs for roosting, resting, basking, mate location, and shelter and for this reason, they tend to be found in higher numbers close to locations that are dense in shrubs. Most of the population gathers around these shrubs during weather that is colder, cloudy, and windier.[10] When the weather is warm, sunny, and the breeze is still, P. argus spends less time in shrub dense habitats and more time in flight and finding host plants in areas rich in calcareous heath. These areas tend to be on exposed hillsides. For this reason, it often appears that the habitat of P. argus shifts with weather conditions.[10]

In addition to choice of habitat due to host plants and topography, P. argus density correlates with the densities of nest of the butterflies' mutualist ants, Lasius niger and Lasius alienus.[3]

Adult P. argus tend to be very sedentary, only moving around 20 metres (66 ft) every day.[6] For this reason, the butterflies colonize on discrete territory and patches of land. Some butterflies, though, disperse and move over a kilometer between colonies. This is rare, however, as these butterflies tend to form metapopulations.[6]

• P. a. argus Scandinavia
• P. a. aegon (Denis & Schiffermüller, 1775) Karelia
• P. a. cleomenes (Fruhstorfer, 1910) Carpathians
• P. a. wolgensis (Forster, 1936) southern Europe, Kazakhstan, Tian-Shan, Tarbagatai, Saur, southern Altai
• P. a. bellus (Herrich-Schäffer, 1844) Asia Minor, Kurdistan, Levant, Caucasus, Armenia, Talysh
• P. a. obensis (Forster, 1936) Ural, western Siberia
• P. a. clarasiaticus (Verity, 1931) eastern Altai, Sayan, Transbbaikalia, western Amur
• P. a. pamirus (Forster, 1936) Pamirs-Alai, Tian-Shan
• P. a. coreanus Tutt, 1909 eastern Amur, Ussuri, Korea
• P. a. micrargus (Butler, 1878) Japan, Sakhalin
• P. a. asur Agenjo, 1966 Villasur, Spain
• P. a. bejarensis (Chapman, 1902) Castilla-Leon, Béjar, Spain
• P. a. branuelasensis (Tutt, 1909) Branuelas, Spain
• P. a. casaiacus Chapman, 1907 Casayo, north-western Spain
• P. a. claraobscura (Verity, 1931) Larche, Basses-Alpes, 1700-2000m, France
• P. a. seoki Shirozu & Sibitani, 1943 Saishuto, Korea
• P. a. vigensis Tutt, 1909 Vigo, north-western Spain
• P. a. sultana (Forster, 1936) Asia Minor

When a male detects a female sitting quiescently, he flies towards the female.[15] As he approaches the female, he flutters his wings in broad sweeping movements and she raises her abdomen while vibrating her half-open wings in a mate refusal posture. The female then flies away and is followed by the male. Once she lands, the male flutters around, either in the air before descending or after landing.[15] The female displays a receptive posture by folding her wings after which the male positions himself parallel to the female before bending his abdomen, spreading the valves, and exposing the copulatory apparatus. He proceeds to attach to the copulatory apparatus and the butterflies reorient themselves into the copulatory position. The intermediate aspects of sexual chase depend on the sexual receptiveness of the female to the advances of the male.[15]

P. argus lays eggs near nests of Lasius niger, the ant with which they form a mutualistic relationship.[2][3] This mutualistic relationship benefits the adult butterfly by reducing the need for parental investment. Once the eggs hatch, the ants chaperone the larvae, averting the attacks of predatory organisms like wasps and spiders as well as parasites. In return, the ants receive a saccharine secretion fortified with amino acids from an eversible gland on the larvae's back. As first instar larvae prepare to pupate, the ants carry the larvae into their nests.[3][2] Once the larvae become pupae, the ants continue to provide protection against predation and parasitism. The butterfly leaves the nest when it emerges in June.

• 
  Egg
• 
  Male
• 
  Female
• 
  Female

• List of butterflies of Great Britain