A browntail moth caterpillar infestation in a chokecherry tree in Brunswick on Wednesday. Shawn Patrick Ouellette/Staff Photographer

BRUNSWICK — The quarter-inch-long browntail moth caterpillars squirmed in their nests this week in a cluster of chokecherry trees in a field across the street from Brunswick Executive Airport.

For now, the caterpillars are still small and emerging from their nests to feed. But they will leave their nests and grow exponentially in the coming weeks, shedding microscopic hairs that become airborne and cause itchy rashes on people in a growing number of areas in the state.

“As the caterpillars get larger, there’s more of those irritating hairs on the caterpillars,” Tom Schmeelk, an entomologist with the Maine Forest Service, said Wednesday as he pointed to a web filled with the tiny caterpillars. “You’ll see them crawling on people’s houses by the end of May.”

How bad infestations will be this season is not yet clear. Populations appear to be down in some parts of southern and central Maine, but the moths are also spreading north and west into new areas.

Cool, wet weather at the end of April through early May could potentially lead to proliferation of a fungus that kills the caterpillars, which would reduce the risk of rashes and other health effects. But Schmeelk said it’s possible the rainy weather came too soon, as the fungus does the most damage to caterpillar populations after rainy weather later in May or June.

The wet weather in early May will help trees survive the infestation, he said. Browntail moth caterpillars tend to populate fruit, oak, birch, elm and poplar trees, and the rain promoted earlier leafing that will help trees survive infestations of leaf-eating caterpillars.


This will be the eighth year of a major browntail moth outbreak that began in 2015 in Maine. Typically, outbreaks last 7-12 years, but the impact of climate change is a wild card and makes it hard to predict when this one will end, Schmeelk said.

Dry, warm weather in May and June is optimal for the browntail moth caterpillars, because it suppresses the fungus and viral pathogens that can knock back moth populations.

“We are trending toward drier springs and longer summers,” Schmeelk said. “Extended summers give the caterpillars more time to feed, so they are going into their winter webs a little healthier and a little fatter.”

Tom Schmeelk, Maine Forest Service entomologist, stands near trees in Brunswick that are infested with browntail moth caterpillar nests. Shawn Patrick Ouellette/Staff Photographer

The range of the browntail moth is extending as well, pushing northward into Penobscot County, as well as inland to Kennebec and Androscoggin counties. The Turner and Leeds areas are expected to see major outbreaks during the next two months, Schmeelk said, as well as Waldo County.

Cumberland County – including frequent hot spots Brunswick, Freeport and Yarmouth – is expected to be less inundated this season compared to last year and 2021, although they will still be present, Schmeelk said. The chokecherry trees in Brunswick had a few nests – also called winter webs – on their branches this week, but Schmeelk said this time last year the winter webs were much more numerous.

Browntail moth cocoon

A late-season population collapse last June in southern and central Maine resulted in the browntail moth creating fewer winter webs in some areas, such as Cumberland, Kennebec and Sagadahoc counties. With fewer webs, caterpillar populations in those areas will be down, Schmeelk said.


The nearly microscopic-sized caterpillar hairs are toxic to human skin, get caught up in the wind and can cause health problems to nearly anyone near infested trees. While a rash similar in intensity to poison ivy is the most common symptom, some people exposed to the hairs breathe them in and suffer respiratory problems as well. The hairs are difficult to see and can also penetrate clothing.


With climate change making Maine more hospitable to the browntail moth, scientists are researching what can be done to keep populations in check.

“We haven’t had this big of a browntail moth outbreak in 100 years ,” said Angela Mech, assistant professor of forest entomology at the University of Maine. “There are still so many questions we don’t know the answers to.”

This summer, Mech will research whether the reproductive cycle of the browntail moth can be disrupted, similar to how scientists discovered a way to disrupt the mating of the spongy moth, another forest pest that has caused massive defoliation.

Mech said the strategy is to identify the chemical composition of the female sex pheromone of the browntail moth and then saturate an area with the pheromone to confuse males and make it more difficult for them to find mates.


The strategy is very targeted – only browntail moths can smell their species’ sex pheromones – and if successful would be an environmentally friendly solution to control the browntail moth population.


While scientists are working on longterm solutions to browntail infestations, property owners can keep populations in check by identifying winter webs and cutting them down from trees. Putting the webs in a bucket of soapy water kills the caterpillars.

When doing yard or landscaping work such as mowing and raking in areas with infestations, wearing long pants, gloves and eye protection, and taking a cool shower afterward can help minimize contact with caterpillar hairs.

Browntail moth caterpillar

Some towns work to control browntail moth populations at the local level.

Scott Couture, tree warden for the town of Yarmouth, said municipal staff go street by street to identify nests, take notes and remove nests in public areas and in the public right-of-way, and also spray trees with pesticides. Couture said they will knock on doors and tell homeowners that they have nests in their backyard and give them information on how to control populations.


But not everyone will take action.

“A lot of people will find out the hard way they are very allergic,” Couture said.

For those who do get the itchy rash, some pharmacies in Maine sell specialized compounds for browntail moth rashes.

Tom Schmeelk, Maine Forest Service entomologist looks over a browntail moth caterpillar infestation in a chokecherry tree in Brunswick on Wednesday. (Staff photo by Shawn Patrick Ouellette/Staff Photographer)

Steve Royer, vice president of pharmacy services for Kennebec Pharmacy and Home Care, said they have been making a “proprietary prescription strength” compound for the browntail moth rash for the past decade, and during the peak of a bad season will sell more than 1,000 prescriptions per week.

He said they have also noticed a shift in where people are coming into contact with the caterpillar hairs. They used to sell much of the compound in Brunswick, but in recent years have sold more in the Rockport and Augusta locations.

Schmeelk said people throughout Maine should be aware of the caterpillars because they are no longer primarily a coastal pest.

“When the browntail moth moved inland and northward, it has taken a lot of people by surprise,” Schmeelk said. “We don’t know how long this outbreak will continue, but we hope to go back to baseline levels at some point, and give people some relief.”

For more information on how to avoid browntail moth caterpillars, go to maine.gov/dacf/knockoutbtm

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