The expansion of the wings is from 3¾ to 4¼ inches. Above, all the wings are rich orange-brown bordered with black, the veins are also black. There are two rows of small white spots round the margins of all the wings, and several orange-brown spots near the apex of the fore-wings. Beneath, the markings are similar, except that the white spots are larger, and the hind-wings are very pale yellowish-brown. The male has a black chitinous spot on vein 2 of the hind-wings which is wanting in the female; the wing-veins in the male are also slightly narrower.
The larva of this insect feeds on most of the different kinds of milkweed (_Asclepias_), and also upon dogbane (_Apocynum_). A single caterpillar, fully grown, which was found in a building in the centre of the town of Wellington, formed the subject from which the figures of the metamorphosis of this insect were taken, but this specimen did not afford sufficient material for an exhaustive investigation of the life-history. The following account, taken from Professor Riley's 'Third Annual Report of the Noxious, Beneficial, and other Insects of the State of Missouri,' is therefore inserted:--
"The egg is invariably deposited on the under side of a leaf, and is conical and delicately reticulate with longitudinal ribs, and fine transverse striæ. It is yellowish when first deposited, but becomes grey as the embryo within develops.
"In about five days after laying the egg hatches, and the young larva as soon as hatched usually turns round and devours its egg-shell--a custom very prevalent with young caterpillars. At this stage it differs considerably from the mature larva; it is perfectly cylindrical, about 0·12 inch long, and of much the same thickness throughout. The head is jet black and polished; the colour of the body is pale greenish-white, with the anterior and posterior horns showing as mere black conical joints, and with two transverse-oval black warts, nearer together, on the first joint. It is covered with minute black bristles, arising from still more minute warts.
"When the young larva is three or four days old a dusky band appears across the middle of each joint, and by the fifth or sixth day it spins a carpet of silk upon the leaf, and prepares for its first moult. After the first moult the anterior horns are as long as the thoracic legs, the posterior ones being somewhat shorter; the characteristic black stripes show quite distinctly, but the white and yellow stripes more faintly. After this it undergoes but slight change in appearance, except that the colours become brighter, and that at each successive moult the horns become relatively longer. There are but three moults, and the intervals between them are short, as the larvæ frequently acquire their full growth within three weeks from hatching.