The Silver-studded Blue (Lycæna Argus = Ægon)
The male of this butterfly (Plate 105) is purplish-blue with a black border on the outer margins, and sometimes black dots on that of the hind wings. The female is sooty-brown, powdered to a greater or lesser extent with blue scales on the basal area; there is generally a series of orange marks forming a more or less complete band on the outer margin of the hind wings, and sometimes on the fore wings also. The under side is bluish-grey in the male, and brownish-grey in the female; the black spots are ringed with white, and on the fore wings there is one at the end of the discal cell and a series of seven beyond; the hind wings have from three to five spots before the discal spot, and a curved series of seven beyond; there is a black-edged orange band on all the wings, and beyond this on the hind wings there is a series of metallic blue centred spots; hence the English name of the butterfly, given to it by Moses Harris, which is certainly more suitable than Petiver’s “Lead Argus.”
In a general way the male is rather larger than the female, but this is not invariably the case. The colour of the male varies in shade, and very occasionally, perhaps, is of a lilac tint; the border varies in width, and is sometimes reduced to a mere line. In the female the orange marks may be of a brownish or yellowish tint, and now and then there may be a series of wedge-shaped blue spots above these marks on the hind wings. On the under side there is a good deal of modification of the black spots as regards size and shape, and occasionally there is at least one extra spot on the fore wings placed between the discal spot and the base of the wing; white markings sometimes appear on the fore wings between the outer series of black spots and the orange band, and with this there is generally a white band in a similar position on the hind wings. Female specimens with splashes of the male colour on one or more of the wings have been obtained, and, more rarely, examples entirely male on one side and female on the other have been recorded.
Frohawk states that the egg both in colour and texture, resembles white porcelain; “all the depths produce a deep purplish-grey shade. The ova are deposited singly, and adhere firmly to the receptacle.”
Caterpillars hatched out from eggs, laid the previous summer, on April 1st to 3rd. They were reared on gorse (Ulex europæus), pupated towards the end of June, and the first butterfly, a male, appeared on July 10th.
The caterpillar figured on Plate 104, when full grown, was reddish-brown, finely dotted with white, and from each dot a tiny hair arose; the stripe on the back and line on the side were black edged with white, head black and shining. This caterpillar was found on the last day of May, crawling on the ground under heather at Oxshott. It was then about half-grown, and was reared on heather, pupated in due course, and produced a female butterfly on July 11th.
The chrysalis, of which two figures are given, had a pale brownish and rather shining head; the body was brown with a darker line on the back; the thorax and wing-cases dull yellowish-green, the former rather glossy. It was placed in an angle formed by a side and the floor of the cage, lying quite flat and secured by silken threads, which, owing to position, I was unable to examine. Some of the caterpillars that Mr. Frohawk reared were pale green with a dark purplish stripe on the back. Another food-plant is bird’s-foot vetch (Ornithopus perpusillus).
The butterfly is on the wing in July and August, and seems to be more often found on sandy heaths than elsewhere. It is especially common, in some years, in the heather-clad districts of Surrey and Hampshire, as well as other counties in England. In Norfolk and Suffolk it is said to be common, but scarce in Gloucestershire and Somersetshire. Its range extends through the greater part of England and Wales, and into Scotland as far as Perthshire. Specimens from the northwest coast of Wales are said to be larger than those from inland localities.
As regards Ireland, there is only Birchall’s record, “The Murrough of Wicklow, and near Rostrevor,” in evidence of the butterfly occurring in that country at all.
Abroad, it appears to range pretty well over the whole of Europe, and through Asia eastward to Siberia, Corea, and Japan.