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Gypsy Moth

A gypsy moth caterpillar on a half-eaten leaf.
Gypsy moth caterpillar.

European gypsy moths were accidentally introduced into Massachusetts in 1869 by an amateur entomologist. Since then, gypsy moths have defoliated millions of acres of trees in forests and urban areas in at least 20 states and the Washington DC area. Gypsy moth caterpillars feed on more than 300 species of deciduous and evergreen trees.

Gypsy moth populations may have a temporary, large increase (an “outbreak”) in an area about every 10 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 cause skin rashes and other reactions in some people. Management options [exit DNR] 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.

Gypsy moths were first found in Wisconsin in the late 1960s in the eastern part of the state. By 1989, they had settled along Wisconsin's eastern shore from Milwaukee to Green Bay. Moths have since been found in every county. The eastern two-thirds of the state is considered generally infested and is quarantined. The quarantine prohibits the movement of items that could harbor gypsy moth eggs, caterpillars or adults and allow them to be moved to uninfested areas. For information on what items are regulated and how to comply with the law, go to the Wisconsin gypsy moth quarantine page [exit DNR].

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

The effort to slow the establishment of gypsy 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 gypsy moth aerial spray program [exit DNR] page.

More information is available on the Wisconsin gypsy moth portal [exit DNR].

Mass of gypsy moth larvae
Homeowners may see gypsy moth caterpillars resting on tree trunks and buildings in June and July.