Gypsy Moth Information

In the winters of 2018 and 2019, Wisconsin saw a decrease in the gypsy moth population due to severe cold temperatures which killed egg masses. Populations have decreased by about one-half since 2017.  Gypsy moth egg counts in the City of Monona have not been high enough to qualify for aerial spraying for the last several years. 

From now until spring, people can help reduce the population of caterpillars next year by treating or removing egg masses. They can be found on trees, vehicles, fences, playground equipment, buildings, or any outdoor item. A gypsy moth egg mass is tan, oval or bulb-shaped, and a little bigger than a quarter. It is flat with a velvety texture and can hold 500 to 1,000 eggs. Egg masses can be removed with a putty knife, stiff brush or similar hand tool and placed into a container of warm, soapy water. Let soak for a few days and discard in the trash. Horticultural oil also can be sprayed onto egg masses. Simply crushing the egg masses will not destroy them.  
For more information, call (800) 642-6684, email, or visit

Suppression Program

The City of Monona participates in the State of Wisconsin's gypsy moth suppression program. The program aims to control the population of this pest, which naturally explodes to very high numbers (called outbreaks) about every 10 years. During outbreaks, the caterpillars are a nuisance and can strip trees of their leaves, defoliating entire neighborhoods or forests by late June. Most healthy trees can survive one such defoliation, but trees that are weak or stressed prior to defoliation may die.

Homeowners who are considering insecticide treatments on their properties should contact an arborist or tree service. The Wisconsin Arborist Association has a list of certified arborists available. Additional businesses offering insecticide treatments may be found in the phone book under Tree Service. Homeowners can also purchase insecticides (some applied as a soil drench) at garden centers and large retailers.

Gypsy Moth Life Cycle

gypsy moth life cycle