Mainers are reporting large swarms of Browntail moths this summer. Credit: Courtesy of Maine Department of Agriculture, Conservation and Forestry

When adult browntail moths swarm under porch lights and street lights, it can resemble a blizzard in July. But beyond the shock of seeing that many moths, there’s a hidden danger: those moths are laying eggs that can create even larger future infestations.

“I’m getting a lot of calls from people wondering what to do about them,” said James Dill, pest management specialist with University of Maine Cooperative Extension. “I tell people to kill them any way they can.”

One female browntail moth can lay hundreds of eggs, leading to hundreds of new caterpillars emerging the next spring. The Maine Centers for Disease Control and Prevention has categorized the invasive species as a public health nuisance.

The browntail moth isn’t new to Maine. It’s actually been here for more than a century. But the summer infestations of the moths as they emerge from cocoons have been getting worse for the last five years.

What’s more is that the caterpillar form of the moth, which emerges from eggs in the spring, can pose a health hazard to humans.

When coming into contact with human skin, the tiny hairs on the caterpillar stage of the moth can cause a rash similar to that of poison ivy. For some individuals, the rash can become quite serious and last several weeks. If inhaled, the hairs can also cause serious respiratory issues for some people.

The adult browntail moth is all white with a wingspan just under two inches. The body is covered with white hairs and a brown tuft of hair at the end of the abdomen, hence the name. The hairs on the adult’s body are not toxic, but that does not make them any less of a health nuisance, according to Dill.

So it’s understandable why people don’t want them around. Dill said he’s been getting reports of massive swarms of the insect swirling around any light left on after dark and collecting on the sides of buildings during the day.

“When the adult moth emerges from the cocoon the hairs on its abdomen are not toxic but it is possible as it emerged some of the toxic hairs that were on that cocoon got on it,” Dill said. “If someone was to handle that moth they could still get a rash from those stray hairs.”

Once the moth starts flying around those stray hairs will fall off, leading to a different sort of exposure risk.

“Those toxic hairs stay in the environment for two to three years,” Dill said. “So even if you don’t see any caterpillars and feel safe, you could come in from raking leaves or mowing grass and discover you have the rash because you have stirred up those stray hairs that are on the ground.”

Those hairs can and do land just about anywhere — on trees, gardens, lawns or decks. As for the adult moths Mainers are seeing, Dill said they are living out their seven-to 10-day lifespan in search of a mate and laying eggs. The more moths a person kills, the better the odds of preventing a female moth from having the chance to lay those eggs.

As for exactly how to kill the moths, Dill has a few suggestions.

The adult moths like to cling to the sides of buildings during the day and can be easily plucked off one-by-one by hand, brushed off with a broom or hosed off with a powerful stream of water. Once the moths are dislodged, Dill they often won’t fly away so it’s a relatively simple matter to scoop them up. Dumping the moths into a pail of soapy water is enough to kill them off.

“They don’t fly during the day so they are easy to collect,” Dill said. “But remember to wear gloves in case any of those stray hairs are on a moth.”

He does not advocate spraying chemical pesticides on the sides of homes or other buildings.

During the caterpillar stage, the moth feeds on various species of trees including apple, maple and oak. Once they turn into a moth they no longer feed and become more of a pest due to the sheer numbers that can collect and swarm around lights at night.

The best way to keep the moths from collecting in the first place is to turn off any light that could attract them. However, Dill pointed out that luring the moths in with light at night allows people to kill as many as possible during the daytime.

Killing even one adult browntail moth before it can lay eggs means preventing the future hatching of hundreds of new toxic-hair laden caterpillars next year.

“You can look at it as doing your part to eliminate the moths,” Dill said.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.