Forest service warns of browntail moth caterpillar infestation in Mid-Coast

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AUGUSTA — The mild winter and early spring has triggered a large-scale infestation of the browntail moth caterpillar, which the Maine Forest Service expects to be most prevalent in five Mid-Coast communities.

Bath, Brunswick, Topsham, West Bath and Bowdoinham are likely to see the greatest infestation, according to the Forest Service.

Charlene Donahue, an entomologist with the service, said the microscopic hairs of the caterpillar can cause respiratory issues or a significant skin rash similar to poison ivy.

Donahue warned that the caterpillar’s presence is likely to cause effects lasting into this fall and next spring. Town officials and the Maine Center for Disease Control have been alerted to the problem, she said.

“We want local residents to be aware of the browntail moth caterpillar infestation so they can take steps now and in coming months to protect themselves and their families from discomfort,” Donahue explained.

Bath City Arborist Thomas Hoerth said he has seen such an infestation there before.

“They probably started showing up about six years ago,” Hoerth said Tuesday. “It’s kind of like a wave, and the eye of the storm has been moving further and further north, and we’re just getting larger and larger infestations.”

Hoerth said he wasn’t sure whether this is the crest of that wave, or “(whether) we’re still riding up the wave. And a lot of that’s going to depend on this growing season and this summer, and it also depends on overwintering conditions.”

“It will subside over a period of time,” he said.

The browntail moth is an invasive species that entered the U.S. in the 1890s on nursery stock arriving from Europe. Donahue said its presence in North America is now limited to the coast of Maine and Cape Cod.

She said weather conditions last year predicated an issue with the moth, with a dry May and cool June leading to an explosion in the population.

Donahue said this year’s warm early spring caused the caterpillar to emerge early, when there still is not much tree foliage for it to consume.

“They’re outstripping their food source,” he said.

Hoerth said the caterpillars “love oak,” but that while the caterpillars will set the trees back, the trees’ substantial food reserves will allow them to re-leaf.

Donahue said the caterpillars create a fine silk strand that allows them to travel on the wind and land on other trees and bushes or the ground.

“That means they’re crawling up people’s houses, on their decks, across the lawn and on every shrub and bush in the area,” Donahue said. Instead of being concentrated on trees, “they’re everywhere.”

The caterpillar is distinctive due to two patches of bright orange on its end. It has toxic microscopic hairs to keep birds from eating it. While those hairs provide a strong defense system, they can also cause an oozy, blistery rash or respiratory distress for people who encounter them.

After breaking off the caterpillars, the hairs circulate in the air. The caterpillars’ molting process produces dried skin containing the hairs, which can drift and also affect people, Donahue explained. She warned that since the hairs remain toxic for a year or longer, people still can be affected in future seasons.

Donahue said concentrated spraying is likely not possible at this point, since the caterpillars have moved from the trees, and extensive planning is necessary for careful pesticide application. There are also specific regulations for the control of the insect near marine waters to protect lobsters from chemicals.

She noted that responsibility for controlling the insect depends on property owners and local communities, while the state will provide assistance and advice.

People can protect themselves by:

• Doing all yard work during wet or damp conditions.

• Mowing when the grass is wet.

• Using water to wash caterpillars off structures.

• Not sitting on lawns.

• Keeping windows shut, particularly on windy, dry days.

• Wearing appropriate clothing like pants and long-sleeved shirts.

• Being aware of conditions while raking leaves or brush this fall or next spring.

• Contacting a health care provider if symptoms occur.

The Maine Forest Service’s Web site offers additional precautions at More information on the browntail moth is available at, and on pesticides at

Alex Lear can be reached at 373-9060 ext. 113 or

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The Maine Forest Service is warning of browntail moth caterpillar infestation in the Mid-Coast, with effects likely to last into this fall and next spring.

A Maine native and Colby College graduate, Alex has been covering coastal communities since 2001, and currently handles Bath, Topsham, Cumberland, and North Yarmouth. He and his wife, Lauren, live in the Portland area, and Alex recently released his third album of original music.