The full-grown caterpillar is black, velvety between the rings, covered with golden brown hair on the back and greyer hair on the sides, among which are some black ones; three interrupted whitish lines on the back; some of the hairs along the middle of the back stand erect and form a ridge, looked at from either end. Head lightish brown in colour, lined with black. Feeds in the spring months and up to June chiefly on various kinds of grass. Among many of the plants that it has been known to eat are trefoils, bird's-foot (_Ornithopus_), sea thrift (_Statice_), heather, sallow, hawthorn, sloe, plum, bramble, etc. With regard to the food, it is interesting to note that although one rearer will find that sallow is excellent for the caterpillars, another considers that sallow or hawthorn are but poor { 121} substitutes for kidney-vetch (_Anthyllis vulneraria_) upon which the caterpillars were feeding when found (Plate 57).
The brownish chrysalis is enclosed in a hard but somewhat brittle, brown, oval cocoon, and when spun upon the surface of the ground, protected by an outside covering of loose silk webbing. In August and early September the moths appear. Emergence from the chrysalis usually takes place soon after midday; the males are early on the wing, and when reared in captivity they should be secured as soon as the wings are dry, or they may spoil themselves in their efforts to escape. Reared females are apt to be deformed, but for "assembling" they may probably be as useful as more perfect examples if the rearer happens to be able to exhibit the attraction in a locality for the species. Both sexes have been taken at electric light.
The best known localities for the species in England are, besides those already mentioned, the sand hills on the Cheshire and Lancashire coast. It is, or has been, found also on the coast of Cumberland; Lyndhurst and Ringwood, in Hampshire; Isle of Purbeck, Poole, Swanage, and Bloxworth, in Dorsetshire; Devonport, Bolt Head, and Salcombe, in Devonshire; and Penzance and the Scilly Isles. Its range extends through Central and Southern Europe to Asia Minor and North Africa.
The male is reddish brown, and the female generally greyish brown, but sometimes is of a reddish grey coloration; the fore wings in both sexes are crossed by two pale ochreous lines on the central area (Plate 59).