Adapted from Annual Invasion of Orangestriped Oakworm in Georgia, by Dr. Shimat Joseph, UGA
If you’ve noticed oak trees looking a little bare in late summer, the culprit may be the orangestriped oakworm, Anisota senatoria. These striking black caterpillars with orange-yellow stripes are native to Georgia and show up almost every year in August and September. While they can strip leaves from oak trees surprisingly quickly, healthy mature trees usually recover just fine because they’ve already stored most of the energy they need for the year.
The bigger issue is often the nuisance they create. Large numbers of caterpillars can shower patios, cars, and sidewalks with droppings (called “frass”) and may be seen crawling across lawns and driveways as they search for a place to pupate. Young, newly planted, or already stressed trees can also suffer more serious damage than established oaks.
Adult moths emerge in early summer and lay clusters of eggs on oak leaves. The young caterpillars feed together as a large group, first skeletonizing leaves and later eating everything except the leaf midrib. By late summer, the caterpillars are fully grown and descend from the trees to burrow into the soil, where they spend the winter before emerging as moths the following year.
Orangestriped oakworms mainly feed on oaks but may also be found on hickory and birch. Signs of an infestation include chewed leaves, falling frass, and groups of caterpillars moving down tree trunks.
Because these outbreaks occur so late in the season, control is often unnecessary. Natural enemies such as birds and paper wasps help keep populations in check. On smaller trees, young caterpillars can be managed with products containing Bacillus thuringiensis (Bt) or neem. Homeowners can also knock caterpillars from branches and dispose of them.
While an orangestriped oakworm outbreak can make a healthy oak look alarming, it’s usually more of a temporary eyesore than a long-term threat. Most established trees will leaf out normally again next spring. I say, sit back, relax, and enjoy that your trees are supporting biodiversity in the landscape!
