Rather large butterflies. Fore wings subtriangular, rounded at the apex, and lightly excavated on the lower two thirds of the outer margin. Hind wings rounded, somewhat crenulate. Egg nearly spherical (see [Plate C], Fig. f) pitted with large hexagonal cells. The caterpillar in its mature state cylindrical, with the second segment adorned with two prominent club-shaped tubercles, and the fifth, ninth, and tenth segments also having raised tubercles (see [Plate C], Fig. h). They feed upon oaks, birches, willows, and lindens, preferably the two latter. The caterpillars after hatching hibernate in little winter quarters, which they make out of the fragment of a small leaf, which they tie together with silken threads, and also secure to the twig by a few strands. The chrysalis has a projecting boss on the back; the head is either rounded or slightly bifid.
PL. XLIV
There are a number of species in the United States, several of which mimic other butterflies in a singular manner, B. disippus closely resembling Anosia plexippus. The caterpillars do not pupate until summer has come; the butterflies take wing when the lindens bloom.
(1) Basilarchia astyanax (Fabricius), [Plate XLIV], ♀ (The Red-spotted Purple).
Our figure gives a good idea of the upper side of the wings. On the lower side the wings are brown, banded with black on the margins, the inner row of marginal spots being red, with two red spots at the base of the fore wings, and four such spots at the base of the hind wings. Palpi white below; a white stripe along the sides of the abdomen. Expanse 3.00-3.25 inches. The egg and caterpillar are shown on [Plate C]. The caterpillar is found on a variety of plants, but most commonly on lindens, willows, and wild cherry trees.
PL. XLV
Found all over the United States and Canada, as far west as the Rocky Mountains, but not in the very hot lowlands of the Gulf region. Is said to occur on the uplands of Mexico.
Between B. astyanax and the following species, B. arthemis, there is more or less affinity. They represent two lines of evolution from a common ancestry, and there are evidences of atavic reversion to type constantly occurring in both forms. They even occasionally interbreed with each other, and hybrids are not altogether uncommon. The whole genus in fact is in a more or less plastic state, and well deserves the careful attention of biologists.