Spongy Moth

The European spongy moth (Lymantria dispar) was introduced into Massachusetts in 1869. Since then, spongy moths have defoliated millions of acres of trees in forests and urban areas in at least 20 states and the Washington, D.C., area. Spongy moth caterpillars feed on more than 300 species of deciduous and evergreen trees.

Spongy moth populations may have a temporary, large increase (an “outbreak”) in an area about every 10-12 years, lasting 2-3 years. Defoliation of susceptible tree and shrub species may be widespread during outbreaks, although healthy trees and shrubs are likely to survive if they are defoliated. High caterpillar numbers can be a tremendous nuisance. In addition, the caterpillar hairs can cause skin rashes and other reactions in some people.

Management options for reducing high populations include: egg mass oils, barrier and collection bands, physically destroying life stages, drowning egg masses and caterpillars in a can of soapy water, insecticidal soaps and insecticide application to high-value trees or forest stands. The DNR has produced a guide to insecticide options for homeowners.

Spongy moth life stages began to be found in Wisconsin in the late 1960s and a handful of isolated, reproducing populations were found between the mid-1970s and mid-1980s. These were successfully treated to eradicate (eliminate) the pest. These infestations likely originated when infested items were moved from other states. In the late 1980s a low-level reproducing population was found in Door and Kewaunee counties, and adult moths were being caught in pheromone traps as far south as the Milwaukee area. Within a few years reproducing populations were also present in Marinette and Oconto counties as well as in southeast Wisconsin. The pest was too widespread to eradicate (eliminate) and it has continued to spread since then. The first noticeable tree defoliation was seen in Oconto County in 1997.

People living in non-quarantined counties may come across spongy moth. If you do, call 1-800-642-MOTH (6684) or email spongymoth@wisconsin.gov to report it and please take these reasonable precautions to reduce the spread of spongy moth.

The effort to slow the establishment of spongy moth continues in unquarantined counties of western Wisconsin. In these counties, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) monitors for the pest using traps and conducts aerial spray treatments on any isolated populations it finds. Find more information on DATCP's spongy moth aerial spray program page.

More information is available on the DNR’s spongy moth fact sheet [PDF]. For help understanding how to tell if a caterpillar is a spongy moth caterpillar or a look-alike species, reference the Caterpillar Comparison (Common Spring Defoliators) fact sheet.