The species is distributed throughout the Palæarctic Region, except the Polar parts.
The Common Blue (Lycæna icarus).
The male is blue, with either a tinge of violet or mauve in its composition. Sometimes, though rarely, it assumes the brighter shade of the Adonis Blue. All the wings are very narrowly edged with black on the outer margins; the veins are generally pale, shining blue, sometimes becoming blackish towards the outer margins, and occasionally continued into the fringes, but not to their tips. The female is most often brown, with some blue scales on the basal area of all the wings; there is a black discal spot on the fore wings, and a series of orange crescents before a row of black spots on the outer margin; the hind wings have an outer marginal row of black spots, edged outwardly with white and inwardly with orange.
On Plate [106,] Fig. [1] represents a typical male, and [Fig. 3] a typical female, whilst the normal under sides of the sexes are shown in Figs. 10 and 11. The size of this butterfly ranges from one inch and a half to three-quarters of an inch. The large specimens at the bottom of the plate are from Scotland.
Scotch and Irish males often have some black spots on the outer margin of the hind wings, as in Fig. [2,] but this is from Ventnor in the Isle of Wight. The female is sometimes of a uniform brown coloration, devoid of blue scales, and, with the exception of slight traces of orange on the outer margin of the hind wings, entirely without marking. On the other hand, this sex is sometimes almost as blue as the male in colour (var. cærulea), but the discal spot, outer marginal borders, and orange markings are present. Occasionally the orange spots give place to yellow ones. The discal spot on the fore wings may be encircled with bluish-white scales, and now and then this spot on all the wings is surrounded very distinctly with bluish-white. I have seen the latter form from Durham and Ireland only, but it probably occurs in other parts of the kingdom.
Quite a number of gynandrous specimens of this species have been recorded, some of them being male on the right side and female on the left, in others the reverse was the case.
On the under side the male is greyish and the female brownish, consequently the white rings around the black spots show up more distinctly in the latter sex. A not uncommon aberration is without spots between the discal spot and the base of the fore wing; this is known as icarinus. Another form that occurs fairly often has the lower basal spot united with the last spot of the outer series, as in Fig. [9,] this is ab. arcua, and a modification, with the junction bar-like instead of arched, has been named melanotoxa. Very rarely the whole of the under side, except the outer margins, is free of spots (Plate [119]). A specimen exhibiting aberration in this direction is shown on Plate [118,] Fig. [6,] whilst Figs. [1] and [3] show modifications of what is known as the streaked form.
I am indebted to Mr. E. Sabine, of Erith, for the loan of all the fine aberrations of the Blues figured on Plate [118.]
On Plate [107] will be found figures of the early stages.