Large, elegant moth, 1 and a half to 3 inch wingspan. Colored in shades of rich browns, often with pink or purple tints. Patterns variable, varying from all one color to elaborate sripes. Forewings long and held out at an angle; hind wings wide, sticking out from forewings at the sides. Body fat, furred, and curving upwards towards tail. Adults fly in the summer. They do not eat, living only to reproduce.

Caterpillar fat and usually green, sometimes red. Eats leaves of walnuts ("juglandis" means "of walnuts"), alders, hickories, beech, hazelnuts and hop-hornbeams. When disturbed, caterpillar whistles or squeaks, which is believed to startle birds that might eat it.

Found from the Atlantic to tthe Rockies in the US and southern Canada.