Spongy moth (Lymantria dispar) is a non-native pest that is well-established in the eastern two-thirds of Wisconsin. The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) focuses its efforts on the western edge of that area in an attempt to slow the spread of this destructive insect. Spongy moth caterpillars feed on the leaves of about 300 species of trees and shrubs. At high populations they may completely defoliate trees in the spring.
(Photo: Spongy moth caterpillar, forestryimages.org)
Repeated defoliations may weaken trees and leave them susceptible to other insects and diseases. Adult spongy moth do not feed, but the adult females lay thousands of eggs which are easily transported to new areas by humans on firewood, outdoor furniture, camping equipment and vehicles.
Fifty-three of Wisconsin's 72 counties are under quarantine for spongy moth. Pockets of spongy moth infestation flare up periodically within these counties. These outbreaks may range from a single woodlot to thousands of acres. Local communities or individual property owners may choose to spray to suppress these outbreaks, but DATCP generally does not treat in these areas.
DATCP does treat in the counties just west of the quarantined counties and on the western edge of some of the quarantined counties as part of the Slow the Spread Program, a cooperative effort with the U.S. Department of Agriculture Forest Service and 10 states.
Note: If you see webs in a tree, it is not spongy moth. It is either tent caterpillars or webworms. Both are native species that may partially defoliate a tree, but they attack only a few species of trees and have natural predators to control them. There is no state program to monitor or control them. You can compare the species here.
Resources
Aerial spraying
Quarantine and regulations
Trapping and egg mass surveys
Fact sheets
Spongy moth on your property
Identifying spongy moth
Information from Partner Agencies
Wisconsin Department of Natural Resources
University of Wisconsin-Extension