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. The chrysalis, which is figured on Plate 116 (after Frohawk), is ochreous when first formed, but becomes darker gradually; the wing-cases, however, remain of the original colour, but their hind margins darken. From a chrysalis found on July 12 the butterfly emerged on July 16. There is some evidence in favour of the supposition that this caterpillar is in some way dependent upon ants for nourishment after the third moult, if not before, but what the exact requirement may be is not known. Probably the circumstances connected with the discovery of the chrysalis in 1905 by Messrs. Frohawk & Rayward may afford a valuable clue to the direction in which their future investigation will have to be conducted. We may hope, therefore, that the mystery that has so long hung over the last stages of the caterpillar will be solved before very long. Lewin (1795) and Donovan (1796) both refer to this as a rare English butterfly. The former states that it is on the wing in July, and is found on high chalky lands in different parts of the kingdom, having been taken on the cliffs in the neighbourhood of Dover, Marlborough Downs, the hills near Bath, and near Clifden in Bucks. Stephens, in 1828, wrote of it as "an insect of great rarity." He mentioned the localities given by the older authors, and added that it had been taken in the Mouse's Pasture, near Bedford, in rocky situations in North Wales, and had been plentiful near Winchester.