Browntail moth caterpillars declining in Maine

Maine (WABI) - There is good news when it comes to the bothersome browntail moth in Maine.

Recent surveys show a drastic *decrease* in the population.

Joy Hollowell tells us more.

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”This is part of its normal cycle where it booms and busts,” says Dr. Angela Mech, Assistant Professor of Forest Entomology at the University of Maine. “So it does look like we’re in the beginning of the bust.”

Browntail moths typically make an appearance every 10-15 years. 2025 marks a decade for this latest outbreak in Maine.

“There are two pathogens that help to control browntail moth populations,” explains Tom Schmeelk, an entomologist with the Maine Forest Service. “One of them is a fungus and one of them is a virus.”

Evidence of both started showing up back in the fall of 2023.

According to the State of Maine Climate Change Institute, 2023 was the wettest summer on record in Maine since 1917, and the second rainiest growing season (May-September) since 1895.

According to the NWS in Caribou, many major population centers in Northeast Maine recorded the 2023 summer as a top 10 wettest summer on record.

“And that really, really helped the fungus and the virus sort of spread,” says Schmeelk. “Also, the population, when it’s at that high of a level, it’s kind of ripe for an eposidic or fungal/viral outbreak to really spread through and kind of take the population down a few notches.”

Last year, the Maine Forest Service conducted two aerial surveys, measuring the amount of browntail moth caterpillars in our state.

“And with both of those aerial surveys combined, we only picked up a little over 2,000 acres for the whole state,” notes Schmeelk.

Compare that to 49,000 acres in 2023 and around 152,000 acres in 2022.

“It’s directly attributed to that wet weather that we’ve had the past two years, which is absolutely wonderful,” says Schmeelk. “We’ve been sort of hoping and praying since this outbreak sort of started in 2015. This would have been the 10-year full outbreak.”

As for the odds of both a fungus and virus occurring at the same time-

“It’s actually quite common,” says Mech. “It’s Mother Nature’s way of making sure that nothing gets out of control for too long. It’s what we’ve been anxiously crossing our fingers for, for this right recipe that would result in the browntail moth population starting that decline.”

But just because the numbers are going down, that doesn’t mean we’re out of the woods yet.

“It is certainly possible that they could make a rebound,” says Schmeelk, smiling. “We have been very surprised before.”

“Right now we have to remain diligent with looking at those winter web nests,” adds Mech. “Now that the leaves are off the trees, we have all these sunny days. And so it’s really the right time to look for those winter nests and clip them if you do see them.”

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For more information on how to clip winter browntail moth caterpillar nests and dispose of them properly, log onto maine.gov.

Schmeelk notes that while the browntail moth population is decreasing in a majority of of Maine, there are still some areas with elevated levels according to the Maine Forest Service.

Those include north of the Bangor area, Northern Knox County, Belgrade Lakes and some areas outside of Lewiston and Auburn.