There is no considerable variation in this species, but the spots on the under side are subject to slight modification in the matters of size and shape; the borders also vary in width, and in the female the blue area is thus sometimes much restricted. A gynandrous specimen has been recorded, in which the right side is male. The egg (Plate 112) is described as whitish or bluish-green in colour. The full-grown caterpillar has a blackish head, the body is bright yellowish-green with paler lines; eight rings from and including the second are crested with two ridges of humps, between which lies the sunk dorsal space; the whole skin of the body is velvety, with its surface thickly covered with yellowish warty granules, each bearing a minute bristly white hair. Sometimes the humps and the middle of the back are marked with rose-pink. The chrysalis is pale brownish-ochreous with a thin blackish-brown line on the back of the brown freckled thorax; the body is marked with rather blotchy arrow-head dashes, and some larger dark brown blotches; the wing-cases are pale greyish freckled and outlined with brown, their surface is smooth and rather more glistening than the other parts, which are thickly studded with fine, short, brownish bristles. (Adapted from Buckler.) The following is a brief summary of a paper by Mr. R. Adkin (_Proc. S. Lond. Ent. and Nat. Hist. Soc._ for 1896), in which he gives a most interesting account of the earlier stages of the second brood of this species. At the time when the butterflies of the second brood are on the wing, the flower-buds of the ivy (_Hedera helix_) are still young, and form compact heads. The butterfly, having selected one of these heads, settles upon its top, closes her wings over her back, and bending her abdomen down and round underneath the buds, affixes an egg to the under side of one of the slender single bud-stalks. In about a week the eggs hatch. The young larva which in colour matches the buds very closely, rests on the bud-stalk with its anterior segments, which completely cover its head, pressed closely against the bud, and looks so exactly like a slight swelling of the upper part of the stalk as to make detection a matter of great difficulty, even with the aid of a fairly powerful lens. The larva is very sluggish in its habits, seldom leaving the head of the buds on which it is hatched, so long as sufficient food remains for its nourishment, or occasionally when about to change its skin. It appears to feed only at night, and its manner of feeding, which is the same throughout its life, is to eat a round hole through the outer shell of a bud, and pressing its head forward through it to clear out the soft inside of the bud. In from four to six weeks it is full-fed; it then quits the buds, and attaches itself by slender threads to a leaf, and in a few days becomes a pupa, in which state it passes the winter.