MADISON, Wis. — The number of invasive insects in Wisconsin is on the rise. One of them, called a spongy moth, is prompting many cities and the entire state to take action.

What You Need To Know

  • One invasive species that is on the rise in Wisconsin is called the spongy moth

  • Little brown patches indicate spongy moths are targeting a tree. The insects grow from brown eggs, then transform into caterpillars, then moths

  • They eat all the leaves and can kill trees

  • It’s important to not just leave the brown egg masses on the ground, or try to crush them, as they can still survive. Instead, you’re urged to soak them in soapy water for two days before throwing them in the trash

Little brown patches indicate spongy moths are targeting a tree. The insects grow from brown eggs, then transform into caterpillars, then moths. They eat all the leaves and can kill trees. They’re known for spreading fast and being hard to get rid of.

Madison City Forester Ian Brown is trying to stop them.

“They typically go in about 10-to-15-year population cycles, and this year just happens to be one of those years that is their peak cycle,” Brown said.

He said rain is crucial in stopping the spread of spongy moths. It doesn’t help that Madison is experiencing a severe summer drought.

“We had a dry spring and summer, so that’s hard on the natural pathogens that would take out or reduce the populations of spongy moth caterpillars,” Brown said.

Workers with the Wisconsin Department of Natural Resources are also out tackling the problem. Forest Health Specialist Michael Hillstrom is focusing on Devil’s Lake State Park, among many other state-owned lands throughout Wisconsin.

“There are areas where we’re already seeing some tree mortality,” he said.

(Spectrum News 1/Natalie Sopyla)

To prevent more trees from falling victim, the DNR is treating some trees with a fluid that kills spongy moths.

“We did what’s called a systemic insecticide injection,” Hillstrom said. “What that means is that the insecticide is either injected into the soil or into the tree itself.”

Part of Hillstrom’s job is showing people what they can do themselves to protect trees on their property. It starts with thoroughly checking them.

“We’re really going to be encouraging people to think about either scraping egg masses off of trees or using an oil product applied on those egg masses to smother them basically,” Hillstrom said.

University of Wisconsin-Madison experts said it’s important to not just leave the brown egg masses on the ground, or try to crush them, as they can still survive. Instead, you’re urged to soak them in soapy water for two days before throwing them in the trash.

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