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Butterflies of temperate Asia
Silver-studded Blue
Plebejus argus  LINNAEUS, 1758
Family - LYCAENIDAE
subfamily - POLYOMMATINAE
Plebejus argus male, Adrian Hoskins
Introduction
Altogether there are about 70 Plejebus species, distributed variously across North America, Europe and temperate Asia.
The males of most species are metallic blue, while females are generally a dull earthy brown, with small orange submarginal lunules. Most species are small and delicate, and have narrow forewings. The undersides are marked with a distinctive pattern of white-ringed black spots, and the orange submarginal lunules are usually prominent, and often studded with a few reflective blue scales.
The commonest and most widely distributed species is idas which occurs in North America as well as in Europe and Asia. It is very easily confused with argus, and the 2 species can only reliably be distinguished alive by examining the forelegs. In argus these are spined, in idas they are not.
Plebejus argus is found across Europe and temperate Asia to northern China and Japan.
Habitats
This species breeds mainly on humid heathlands and in damp meadows and valleys, but it also occurs on calcareous and silicaceous grasslands.
Lifecycle
At most heathland sites the eggs are laid singly in July at the base of young shoots of cross-leaved heath Erica tetralix, heather Calluna vulgaris, bell heather Erica cinerea or gorse Ulex europaeus. On limestone sites the eggs are laid on the stems of bird's foot trefoil Lotus corniculatus or rockrose Helianthemum chamaecistus, very close to the base of the plants. The eggs are always laid close to nests of the ant Lasius niger.
The larva develops within the egg in the late summer but doesn't hatch until the following March. It feeds by day on the flowers and tender leaf tips of the foodplants. The larva is constantly attended by the ants which milk it to obtain a sugary substance exuded from an eversible gland on its back. In return the larva gains protection because the presence of ants deters predatory wasps, spiders and carnivorous bugs.
When ready to pupate, the larva is driven or carried into the ant's nests. The pupa is attended by the ants until the butterfly is ready to emerge in late June or early July, at which time it crawls out of the nest and makes it's way up a stem where it settles to expand and dry it's wings.
Adult behaviour

The steely blue males are easily seen, as they flutter incessantly over heather or grasses in search of females, stopping occasionally to nectar at bell heather, bird's foot trefoil or rockrose. Females are much harder to find, as they are far more sedentary and duller in colour, being earthy brown with an indistinct series of orange sub-marginal lunules.

When the sexes meet, copulation takes place almost immediately, with no observable pre-nuptial ritual. Mated pairs can sometimes be found basking with wings in the characteristic three-quarters open position. They remain in cop for about an hour.

Overnight or in overcast weather conditions the butterflies roost on cross-leaved heath, heather, or less commonly amongst grasses or on bushes; adopting the typical head-downward posture shown in the above photograph.

On sunny days the butterflies are active until sunset, and at certain sites can sometimes be found basking in groups of 30 or 40, congregating on bushes or heather clumps to soak up the last remnants of sunlight before going to roost or the night. In the morning these same groups bask communally for about half an hour prior to taking flight.

Plebejus argus male, Adrian Hoskins

 

 

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