Gypsy Moth

Wisconsin Gypsy Moth Slow the Spread Program

Through the Slow the Spread (STS) program, the Wisconsin Department of Agriculture, Trade and Consumer Protection works to delay the spread and establishment of gypsy moth in western Wisconsin.  In its caterpillar stage, the gypsy moth feeds on the leaves of more than 300 different species of trees and shrubs. It is especially fond of oak leaves. In high populations, the caterpillars may completely strip, or defoliate, trees. Healthy trees can usually withstand about two years of defoliation before they are permanently damaged or die.

The department conducts aerial spraying, trapping surveys and egg mass surveys for gypsy moth. The department also deals with quarantine issues and regulations for nurseries, paper and lumber mills, and moving companies to help prevent accidental spread of gypsy moth. To date, 50 of Wisconsin's 72 counties have been quarantined for gypsy moth.
In central and eastern Wisconsin, where gypsy moth is established and outbreaks threaten to cause damage to our forests, the Wisconsin Department of Natural Resources operates a separate program called the Gypsy Moth Suppression program to suppress high populations of gypsy moth by aerial spraying. 

Aerial spraying
Fact sheets about gypsy moths, treatments and regulations
Trapping and egg mass surveys
Quarantine and regulations
DNR gypsy moth suppression program
University of Wisconsin-Extension information
Other resources 

Management zones in Wisconsin

There are three defined zones in a spreading infestation. One is the infested zone, in which the gypsy moth population is well established and colonies overlap. The second zone is the transition zone, in which isolated pest populations have developed, but are not generally overlapping. The third zone is the uninfested zone, in which small populations have developed ahead of the transition zone. 
See diagram below. 
GM chart

Three programs aimed at managing the gypsy moth are in force in Wisconsin. The programs mirror the three zones defined in a spreading infestation.

The Slow the Spread Program (transition zone), which is overseen by DATCP, focuses on monitoring, detecting and reducing isolated populations to slow the gypsy moth's movement across the state.
The Eradication Program (uninfested zone), also overseen by DATCP, focuses on monitoring and detecting any populations that may have jumped out ahead of the transition zone. Treatments are designed to eradicate isolated populations.
The Suppression Program (infested zone) is in areas where the gypsy moth is well established and treatments are performed at the voluntary request of the landowners. The Suppression Program is overseen by the Department of Natural Resources.

What is the Gypsy Moth?

The gypsy moth (Lymantria dispar) does not belong in Wisconsin or anywhere in North America. It is an invasive leaf-eating insect from Europe that has established in parts of Canada, the northeastern states and the upper Midwest, including the central and eastern parts of Wisconsin. Today, the gypsy moth continues to creep westward into the backyards and forests of the state. Go to the University of Wisconsin-Extension Gypsy Moth website to learn how to identify the insect.

GM Caterpillar

What is the Concern?

The gypsy moth is an unusual species. Its population goes through cycles of abundance—from typically low numbers to short-lived explosions in what is called an outbreak. During outbreaks, the hordes of gypsy moth caterpillars strip entire forests of leaves. Trees that were healthy typically can survive a single defoliation, but weak or stressed trees can be killed. Outbreaks can be localized to a single woodlot or stretch over thousands of acres. During outbreaks, the leaves of most types of trees will be eaten because the gypsy moth caterpillar is not a fussy eater. It will feed on both broad-leaved trees and evergreens. The tree species it favors such as oak, birch and aspen will be the worst defoliated. However, most trees in Wisconsin forests will be affected to some degree during outbreaks.

Tree Defoliated

What If I Find Gypsy Moth?

If you find gypsy moth west of the quarantined area, report your find to DATCP by calling the toll-free gypsy moth information hotline at 1-800-642-6684 or e-mailing This information could be used by the STS Program.

If you find gypsy moth within the quarantined area, there may be no need for immediate concern. In most years, gypsy moth will be at low levels and pose no threat. If populations are increasing to damaging levels, however, you may want to take action. Go to for directions on monitoring gypsy moth using predictive surveys and options for managing the pest for yards and woodlots.

History of the Gypsy Moth

In 1869, French lithographer and amateur entomologist Etienne Leopold Trouvelot imported gypsy moths from Europe to Medford, Mass. Trouvelot hoped to breed them with silkworms to produce a hardier species. Unfortunately, a few gypsy moths escaped and had since spread westward throughout the northeastern states, portions of Canada and into the upper Midwest. It was first found in Wisconsin in 1971. Gypsy moth is usually spread unintentionally on campers, nursery stock and even patio furniture infested with egg masses.