The "White Admirable Butterfly," as it was called by some of the older English entomologists, needs only to be seen to be at once recognized (Plate [33]). The white markings on its blackish wings are somewhat similar to those of the Purple Emperor. As in that butterfly, so, too, in this, the most beautiful ornamentation is found on the under side. The shape of the wing is, however, very different in the two butterflies, and there is no probability of confusing one with the other. A somewhat uncommon form is shown on Plate [31] (also kindly loaned by Mr. Sabine); this is var. nigrina. Intermediates also occur, but these, too, are also rather rare. The eggs, which I have not seen, are stated to hatch in about fourteen days, and are laid in July. They have been described as pale green in colour, and of the shape of an orange, but flatter at the base and top.
The caterpillar (Plate [30]) when full grown is dark green on the back and lighter on the sides, roughened with yellow dots, and with a yellow-marked white line above the feet. The bristly spines are reddish with pinkish tips, and those on the second, third, fifth, tenth, and eleventh rings are longer than the others. The first ring seems to be without spines, but the brownish head is set with short ones, two on the crown being rather longer and blacker than the others, and are inclined backwards.
In the autumn, when still quite tiny, it constructs a winter retreat (hibernaculum) (Plate [30]) by fastening a growing leaf of sallow to a twig with silken threads, and then, using more silk, it draws the edges of the leaf together, and so forms a secure chamber wherein it can rest until the following spring, when it quits the domicile and sets to work on the tender foliage around it. At this time the caterpillar is brownish in colour. The chrysalis is of the remarkable shape shown on the plate. It is brownish, with purplish or olive tinge; behind the rounded hump there is a patch of bright green, and above the wing-cases a beautiful golden sheen. There are also other metallic spots and dots on various parts. Altogether, it is one of the prettiest of British butterfly chrysalids.
I am tempted here to quote Buckler's excellent description of the pupation of this species, as it will serve to show the remarkable method by which caterpillars are able to perform a seemingly impossible feat; that is, to get absolutely free of the old skin whilst hanging head downwards from the silken pad or button to which they attach themselves by the anal claspers when preparing to pupate.
Pl. 28.
Purple Emperor.
Egg enlarged; young and full-grown caterpillars; chrysalis.