New Wave of Caterpillars Defoliating Oak Trees

By ecoRI News staff

Orange-striped oakworm caterpillar. (Michigan State University)

Orange-striped oakworm caterpillar. (Michigan State University)

The Rhode Island Department of Environmental Management (DEM) recently reported that small concentrations of orange-striped oakworm caterpillars have begun defoliating trees in areas of western Rhode Island.

The caterpillars feed on the foliage of all species of oak trees, and have been detected in forested areas in central Scituate and Coventry and parts of Foster that were previously stressed by gypsy moth and forest tent caterpillars. Other areas in the state may also be affected, according to DEM.

Unlike gypsy moths, the orange-striped oakworm is native to North America and can be found throughout New York and New England. Although outbreaks of orange-striped oakworm occasionally cause widespread defoliations lasting two to four years, insects, diseases and other natural enemies build up over time and reduce the population to tolerable levels, according to DEM. Pockets of defoliation are typically less than 1,000 acres. In 2005, nearly 16,000 acres were affected in central Scituate and Coventry, according to state officials.

Orange-striped oakworm defoliate trees in late summer/early fall and don’t pose a significant harm to trees, because the leaves have finished photosynthesizing and are beginning to harden off for winter.

“We see some amount of defoliation from this native insect every year. It's not generally a problem because defoliation happens so late in the year, and we normally wouldn’t expect to see much additional tree death,” said Heather Faubert of the University of Rhode Island Department of Plant Sciences and Entomology.

However, because oak trees have already been stressed this year by drought and gypsy moth defoliation, measurable tree mortality is expected. If standing dead trees become a safety hazard they should be removed, according to DEM. Homeowners are encouraged to seek the services of a Rhode Island licensed arborist to provide that service.

Standing dead trees, however, can be beneficial, as they provide homes to many cavity-nesting birds and perches for raptors.