The female generally has the veins of the fore wings of a browner tint than in the males.
This butterfly is one of the very local species, though its food plants are everywhere to be found, in more or less abundance.
The following localities, among others, have been recorded as producing it:—Herne Bay, and other parts of the Isle of Thanet, plentifully; near Faversham, Kent; Horsham, Sussex; New Forest; Brington, in Huntingdonshire; near Cardiff, South Wales, plentiful.
The caterpillars are gregarious, feeding under cover of a silken web. The hawthorn and the sloe are its chief food plants in this country, but it is here too rare an insect to do much damage. Not so, however, on the Continent, where it is extremely common, and is classed among noxious insects, committing great devastation among various fruit trees, especially the apple, pear, and cherry.
But even in this country the insect is occasionally met with in great profusion, but only in isolated spots. Mr. Drane, writing from Cardiff to the Zoologist, says, "In the middle of April (1858) I found the larvæ feeding by thousands upon insulated shrubs of Prunus Spinosa (Common Sloe), eating out the centres of the unexpanded buds, or basking in the sun upon their winter webs."
The body of the adult caterpillar is thickly clothed with whitish hairs, is leaden grey on the side and underneath, black on the back, and marked with two longitudinal reddish stripes. Found from the middle of April to the end of May.
The chrysalis, shown at fig. 14, [Plate I]., is greenish white, striped with yellow and spotted with black.
The butterfly appears in June.