In late April, many homeowners have begun to notice the caterpillars of the common oak moth, Phoberia atomaris. This caterpillar has been found feeding primarily on post oaks and other white oaks in the Anderson, Chapin, and Irmo areas, but they could occur throughout the state. At one residence, the caterpillars were found wondering from the host tree on to the porch and into the garage, leaving a trail of rusty colored vomit.
The common oak moth occurs sporadically through the eastern United States, from Massachusetts to Florida and west to Texas and Kansas. There is only one generation (egg, larva, pupa, and adult) per year; the ground-dwelling pupa is the overwintering stage. Early each spring just before buds break, adults emerge from the pupa and mate. Female moths lay eggs and the caterpillars feed on the newly emerging leaves. The caterpillars are variable in color: they are smooth, brown mottled with white, tan, and black; the prolegs on the third abdominal segment are half the size of the prolegs on the fourth abdominal segment, which are smaller then the prolegs of the fifth and sixth abdominal segment. On the seventh abdominal segment there often is a conspicuous white spot above the spiracle.
The tattered foliage or completely defoliated trees, caterpillar frass (waste material), and wondering caterpillars can be a nuisance to homeowners. However, there is no long-term affect for most healthy trees and most trees will put out another flush of leaves. Typically, a tree that is defoliated for many years in a row and are stressed due to other factors may experience some tree decline (such as limb loss) or, in the worst case, tree mortality. Natural enemies usually keep the caterpillar numbers in check. Luckily for homeowners, in the next few weeks the caterpillars will form an underground pupa where they will remain for the winter.