Browntail moths cluster lights at the Winthrop Commerce Center. File photo

Warm, humid and dry spring weather helped fuel an explosion of browntail moth caterpillars, a toxic pest that has left Maine residents reeling and officials struggling to manage their soaring numbers.

Browntail moths are most common along Maine’s coast and on Cape Cod, but they have been spotted this year in all of Maine’s 16 counties, said Tom Schmeelk at Maine Forest Service Insect and Disease Lab.

According to Schmeelk, the adult moths are typically out in the second week of July. One key to keeping them away from your property is to turn off your lights at night, he said.

“They are over two weeks early this year and are active through August, so late June to August is the time for blackouts at night,” Schmeelk said. “There is nothing much that can be done to control the outbreak of these moths. We have been suggesting people to turn off their outside lights between 9 p.m. and midnight.”

Browntail moths are like any other forest pests that move in outbreak cycles, Schmeelk said, and these outbreak cycles can last between seven and 10 years.

“This outbreak started in 2015, so we’re in the sixth year of it,” Schmeelk  said. “Usually a fungus named Entomophaga aulicae brings the browntail moth outbreak cycle to an end. This fungus spreads and proliferates in the cool conditions of May and June, and it affects the caterpillars.”


Meanwhile, David S. Page, a chemistry and biochemistry professor at Bowdoin College, who researched on how to deal with browntail moths, said UV light bug-zappers available in the market can help cut down the moth population in small areas. He conducted an experiment on an Oak tree infested with moths near his house.

“I used a 40 watt zapper unit to conduct the experiment set up about 6 feet off the ground,” Page said. “Alongside which I used a two-sided yellow sticky insect paper clipped to a wooden bar next to the zapper to catch attracted, but not zapped moths. The results have been gratifying. Each morning there were many moths either zapped, stuck to both sides of the sticky paper or resting dormant on the oak tree near the zapper.”

According to Page, during the height of the moth season in July, the average nightly haul is around 50 browntail moths. This translates to 10,000 to 20,000 eggs not being laid.

“Over the years, this approach has kept the number of browntail caterpillars in our yard very low,” Page said.

Page mentioned this strategy of moth management is effective for individual yards.

However, Schmeelk said that management of the adult moths is not really effective.


“It is mostly males that are drawn directly to the lights with the females hanging out on host foliage outside of the reach of the light,” Schmeelk said.

According to Schmeelk, it’s just not browntail moths that are killed when using UV light bug zappers, but also other parasitic flies and wasps that attack the moths, reducing their impacts to the moth population.

He added that it is the female moths that are crucial in keeping the population levels high so killing just the males won’t really make a dent in the population, especially in heavily impacted areas.

According to the Maine Department of Health and Human Services, after people come in contact with the caterpillar’s hair, they can develop a red and bumpy rash that is similar to a reaction to poison ivy that can linger for a few hours to several weeks.

People are finding the invasive pests everywhere.

“Our son got it from school, but my wife and I are unsure where we got ours,” Adam Daigle, a resident of Lisbon, whose entire family suffered from moth rashes said. “We broke out into rashes almost all over the body. The worst part of the rash is, it’s itchy. The redness and bumps lasts for almost three to four days.”

Meanwhile, a team of researchers at the University of Maine are researching ways that could help prevent future outbreaks of these moths by tricking them with their own sense of smell.

“We are committed to supporting research at the University of Maine,” Schmeelk said. “Moreover, we are also disseminating information to the public to help keep them aware of what is going with moth infestation in the state.”

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