The head is large with a broad reddish lateral band on each side. The back of the body usually has a reddish or purplish, saddled-shaped patch, but it may be indistinct or absent. Each female lays up to 500 eggs singly on the underside of host leaves. The eggs hatch in about 8 to 10 days. As larvae increase in size, the entire leaf, except for the principle veins, is consumed.
Older larvae strip the leaves except for the petioles.
The larvae molt four times before becoming fully grown in late July or early August. They then crawl down the tree trunk or drop to the ground. Pupation takes place in the litter or rarely, in the upper two inches of soil. Some larvae spin a loose, silken cocoon in which to pupate. Starvation and disease also bring an end to outbreaks.