| Importance. - These oakworms occur throughout the United States. The first indication of their presence is often fecal pellets on the driveway or sidewalk under an oak tree. 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. As the caterpillars mature, they are often seen crawling along sidewalks and driveways, yards, etc. searching for a place to pupate.
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. Eggs are white, but become pinkish to brownish gray before hatching. 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.
Full-grown orangestriped oakworm caterpillars.
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. -There are 5 instar stages that mature in May or early June. These first generation adalts females moths oviposit eggs clusters in June and July. The deposited egg clusters are of several hundred eggs on the underside of leaves that 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. Second-generation moths occur in October and November when they oviposit eggs that hatch into overwintering larvae. There are 2 to 3 generations year.
Control. - Natural enemies generally prevent widespread defoliation. Chemical control may be needed for high value trees. The best way to treat your plants for worms is with Bacillus Thuringiensis or Bt. ( a biological control agent that only targets and kills the pest ). Also known in garden centers under the brand name Thuricide, Cry-Maxx or Despel. It is an organic product, though use standard application precautions just to be safe. It targets kills caterpillars (worms) and not most beneficial insects.