Forest Health Protection, Southern Region

Importance. - These oakworms occur throughout the eastern United States. They are voracious feeders, and where abundant, quickly strip the trees of their foliage. Since defoliation takes place in late summer to fall, however, forest stands of white and red oak are generally able to survive with only minimal growth loss or crown dieback. The greatest damage is the aesthetic impact and nuisance the caterpillars create in urban areas.

Identifying the Insect. - The larvae of the orangestriped oakworm are black with eight narrow yellow stripes, the pinkstriped oakworm larvae are greenish brown with four pink stripes, and the spiny oakworm larvae are tawny and pinkish with short spines. Larvae are about 2 inches (50 mm) long and have a pair of long, curved "horns". The adult moths are a similar yellowish red, with a single white dot on each of the forewings.

Identifying the Injury. - Young larvae feed in groups, skeltonizing the leaf. Later they consume all but the main veins and usually defoliate one branch before moving onto another. Older larvae are less gregarious and can be found crawling on lawns and the sides of houses.

Biology. - Adult moths appear in June and July and deposit clusters of several hundred eggs on the underside of leaves. The eggs hatch within a week, and the larvae feed during July to September for 5 to 6 weeks. The pupae overwinter in the soil. The orangestriped and spiny oakworms have only one generation per year, while the pinkstriped oakworm has two generations.

Control. - Natural enemies generally prevent widespread defoliation. Chemical control may be needed for high value trees.