When on the wing, this species might easily be mistaken by the inexperienced for the common Cabbage {78} White; and, by virtue of this _incognito_, does in all probability often escape from the terrors of the net, which would speedily entrap him, were his real character known to the young hunter; for this butterfly is one of those called, in entomological slang, "_a good thing_"--a term expressive neither of superior excellence nor beauty, but meaning that the insect can't be met with everywhere, or every day, and when seen is always to be caught. A closer view, however, shows it to be very distinct from all the other "Whites;" its _decided black veinings on a milk-white ground_, in conjunction with its large size, being sufficient for its immediate recognition. The outline of the wings, as well as the play of the veining lines on their surface, is extremely elegant. It will be observed, that instead of the feathered fringe that surrounds the wings of most butterflies, they are bordered in this species by a stout nervure, forming a sharp black outline, and giving a peculiarly chaste finish. The under side differs in no mentionable respect from the upper--a very rare circumstance in this tribe. From being very sparingly coated with scales, the wings are semi-transparent, differing much in this respect from those of the Garden White butterflies. 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. {79} 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.