White frothy egg masses over winter on the mother cocoon, under bark scales, or some other protected place. The eggs hatch during mid June and the caterpillars feed for about five or six weeks. When the larvae mature, they seek a protected place often on the trunk of the tree, spin their cocoons, and pupate. The adults emerge about two weeks later. The female moth is grayish-brown, about half an inch long, and is wingless.
Males are reddish-brown and are active flyers.
After emerging, the females lay from 300 to 700 eggs on their cocoons. Some years there may be two broods with a second appearing in late August or September. Small infestations may be controlled by removing egg masses from the affected trees and any nearby structures. The cocoon that the egg mass is attached to is made up of caterpillar body hairs, so heavy clothing, eye protection, and a dust mask may be necessary to prevent contact with the irritating hairs. The egg masses must be collected and destroyed since any eggs that fall into the grass below will probably hatch.