The moths appear in June and July. The female moths lay clusters of eggs on the under surfaces of oak leaves. When the larvae hatch, they are small and greenish yellow. When small, the caterpillars typically feed in groups and eat all of the leaf except a lacy network of veins. Orangestriped caterpillars mature and reach their full size by early fall.
Older caterpillars are black with yellow or orange stripes running the length of their bodies.
Older caterpillars tend to be solitary eaters. They eat all of the leaf but the main vein. As a result of their feeding, small trees may lose all their leaves by midsummer. While healthy trees can tolerate feeding by oakworms, young trees may be weakened if they lose all their leaves several years in a row. Mature trees may lose enough leaves to suffer twig dieback as a result of sunscald damage.