TURNER — Looking for an excuse to shirk mowing the lawn or raking those fall leaves still scattered about the yard?

The pesky browntail moth caterpillar will provide that excuse, especially if one is sensitive to its toxic, microscopic hairs.

They can cause a blistery, oozy rash or respiratory distress in people who come in contact with them, Maine Forest Service entomologist Charlene Donahue said Wednesday.

“You don’t even have to come in contact with the caterpillar itself, because the caterpillars molt five times as they grow bigger,” she said.

The hairs will break off the shed skins and blow in the wind.

“So, just being outside can be enough to give you a rash, which is pretty nasty when we’re trying to get people to be outside more,” she said.

The browntail moth is an invasive species that arrived in the U.S. in the 1910 nursery stock from Europe, Donahue said. It moved through Massachusetts, Maine, New Hampshire and Nova Scotia before the population collapsed. Now, it’s only found in Maine and Cape Cod.

On Tuesday, the Forest Service issued an alert, warning of a spike in infestations. Winter web surveys revealed “extremely high levels of browntail moth caterpillar over-wintering webs in the tops of oak trees” in the Brunswick area.

This year, the noxious caterpillar has doubled its population in Brunswick, Bath, West Bath, Topsham and Bowdoinham. It’s also being found in Turner, Lewiston and Augusta.

“It may be in other places and we haven’t found it yet,” Donahue said. “The public needs to be aware of it.”

In Lewiston, webs have been found in only a few trees; but in Turner, she found an 8-mile stretch of trees containing scattered webs.

“If you’re in an area where there’s an infestation, you don’t want to rake your leaves and you don’t want to mow your lawn when it’s dry, because you can stir up more hairs,” Donahue said.

“The toxin is very stable,” she said. “It can last for multiple years, so, if you’re sensitive to it and you mow the lawn next summer, you can still come down with the rash. It’s like poison ivy. If you cover up, that can really protect you.”

In the fall, browntail moth caterpillars build nests in trees from one leaf tightly wrapped with large amounts of white silk, according to a Forest Service bulletin.

A colony consists of 25 to 400 larvae, which over-winter in web nests that are 2 to 4 inches long and situated on branch tips.

They attack hardwood trees, preferably red oak, apple, crab apple, cherry, poplar, birch and elm, Donahue said.

The larvae become active in April, crawling out of the nests to eat foliage as fast as it develops, and they continue to feed on trees through June.

The activity stresses the tree, forcing it to expend more energy to grow out more leaves and it can eventually kill a tree over a number of years, she said.

So what’s sparking the outbreak and what precautions can be taken?

“That’s the $64 question,” Donahue said of the cause. “There’s so much we don’t know about insects.”

Browntail moth caterpillar populations fluctuate, but why they stay up and as high as they are right now is anyone’s guess, she said.

There are parasites and predators that will work on populations, and diseases if weather conditions are right. Webs in small trees like crab apple and cherry can be pruned out now and soaked in a bucket of soapy water or burned, Donahue said.

For webs in the tops of oak trees, the only control is chemical treatment applied by licensed pesticide applicators who have the equipment and offer the service, Donahue said.

She’s assembling such a list now and will make it available by calling her at 287-3244 or email Charlene.donahue@maine.gov.

Pesticide treatment should be done in May, she said.

“This is nothing that a homeowner can control on their own,” she said. “It’s best to work with your neighbors, so you can get rid of browntail moths in a larger area.”

tkarkos@sunjournal.com