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Pl. 117.
Large Blue. 1, 5 male; 2, 3, 4, 6 female.
Chalkhill Blue vars. 7 female; 8 do. var. syngrapha.
The Large Blue (Nomiades arion).
The butterfly on Plate [117], Figs. 1-6, is the largest "Blue" found in this country. All the wings on the upper side are deep blue, and their outer margins are bordered with blackish; the discal spot, and a row of spots beyond, are black; the hind wings have a row of black dots on the outer margin, and sometimes, and especially in the female, there is a series of black dots just beyond the central area; the fringes are white. The under side is greyish tinged with blue towards the base of each wing, but covering nearly the whole of the basal third of the hind pair; the spots are black ringed or edged with white; on the fore wings there are two in the discal cell and a row of six beyond; on the hind wings there are four or five before the discal spot, and a series of seven beyond; all the wings have a double marginal series, and some black dots at the ends of the nervules. Sometimes the wings have a purplish tinge, and this is more usually so in Gloucestershire specimens. The chief variation is in the number and the size of the spots; these are occasionally only faintly in evidence, but more rarely perhaps those beyond the discal spot on the fore wings are of large size and bar or wedge-like in shape; the smaller cell-spot is often absent. A dwarf form is stated to occur at times in all localities.
The complete life-history of this species has yet to be ascertained; no one seems to be acquainted with the caterpillar after hibernation. Pretty much all that is known of the early stages has been worked out by Mr. Frohawk, who has published some very interesting accounts of his observations in the Entomologist for 1899 and 1903, and from these the following details have been obtained.
The egg (Plate [116]) is bluish-white in colour, and is laid singly among the buds of wild thyme (Thymus serpyllum).
Caterpillars hatched on July 10 from eggs received the previous day; they were placed upon thyme blossoms and soon commenced to feed, one being observed to eat its way into the base of the calyx so that the forepart of the caterpillar was hidden. In its colouring and downy covering the caterpillar so closely resembles the flower-buds of the thyme that it is very difficult to detect. After the third moult (July 26) the colour is a uniform, dull, ochreous-pink; there are four rows of long curved hairs, each row composed of a single hair on each ring from the fourth to the ninth inclusive; the first three rings have each a set of three subdorsal hairs, those on the first ring curving forwards; the bases of the hairs resemble glass-like pedestals with fluted sides. The head is ochreous with dark brown markings in front. The caterpillar at this stage develops an aversion to thyme or any other plant offered to it, and seems to be anxious to hide itself in the ground.