David Rieck points to a gypsy moth and batches of moth eggs, which he spotted recently in Janesville's Lustig Park.

Janesville resident David Rieck is no bug expert, but he and his wife have noticed a troubling presence in Lustig Park near their home. Over the course of the past few weeks, they have witnessed the prevalence of a pesky insect known as the gypsy moth.


Masses of eggs of gypsy moths, invasive insects that defoliate trees, have been spotted in Lustig Park in Janesville.

The gypsy moth, or the European gypsy moth, is an invasive species that wreaks havoc on forests. Especially damaging are the larvae—caterpillars that devour leaves until they defoliate trees. These winged insects lay eggs in masses on the bark of trees, sides of houses or other protected areas.

Ethan Lee, parks supervisor for Janesville’s Parks Division, said he is currently in contact with both the Wisconsin Department of Natural Resources and state entomologists to explore options to address the issue in the park. He also said it does not seem there are egg-laying gypsy moths in other areas of the city, but Lee said he has instructed his staff to keep an eye out for signs of the moths and their egg masses.

The eggs are typically laid in August, according to UW Extension’s website on the moths, and the larvae develop over the course of about a month in the warmth of late summer. Then, still inside the egg, the larvae enter into diapause—a sort of hibernation that lasts through the winter—and don’t hatch until mid-May. By then, the trees have expanded their leaves and the caterpillars are ready to feast.

The bugs begin an ascent to the tops of trees to feed on foliage for six to eight weeks. While healthy trees can withstand the moths’ munching, more susceptible trees can be exposed to disease or even be killed outright.

In the past, Wisconsin deployed a successful statewide spraying program, which included Janesville. However, the moths come and go in cycles, which leads to sporadic infestations.


Gypsy moths lay their eggs in masses, which then hatch and produce larvae that feed on the foliage of trees.


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