Tiny browntail moth caterpillars are starting to emerge from their winter webs at the tops of oak trees, looking for leaves to feed on and setting the stage for what the Maine Forest Service says may be the worst season yet of scratching and wheezing on the Maine coast.

The caterpillars, now only a quarter of an inch long, are creeping into more parts of the state, exposing greater numbers of people to the poison ivy-like rash and respiratory problems caused by contact with the caterpillars’ hair.

Wolfe’s Neck Woods State Park in Freeport is bracing for another season of browntail moth caterpillars. Park Ranger Michael Frey looks for concentrations of nests at the park, where they continue to be a problem despite the use of a biological spray that’s employed there. Derek Davis/Staff Photographer

In two years, the range of high-risk areas for infestation has expanded from Brunswick, Topsham and Freeport and nearby into Yarmouth, Falmouth, Gardiner, Boothbay Harbor, Auburn, Nobleboro, Richmond and many other towns. The caterpillars haven’t reached Portland in high numbers yet, but every year they slink closer to infesting the city, Scarborough and Westbrook.

The widening problem has also made its way to the State House in Augusta, where Maine lawmakers are considering a bill to combat the growing browntail moth problem with $274,000 in funding for research at the University of Maine, which collaborates with the forest service. Scientists are trying to figure out effective ways to control the population.

For now, the itching season has nearly arrived, and in a week or so the caterpillar hair will start finding the skin of many Mainers. The peak season for getting rashes lasts for about a month.

In some cases the rash may go away quickly, but for others it can persist and make springtime and early summer much less pleasant.

“This rash can hang on for weeks,” said Michael Frey, park ranger at Wolfe’s Neck Woods State Park in Freeport. The park posts signs starting in mid-May warning visitors of the browntail moth hazard. It also stops accepting school field trips around that time to avoid exposing children to the rash.

This season – especially in the Freeport, Brunswick, Yarmouth and Falmouth areas up through Wiscasset and some points inland – is predicted to be among the worst in recent memory for the browntail moth. The high season for the caterpillars that cause the rash is mid-May to mid-June, as the caterpillars turn into moths by early July.

During high season, the nearly microscopic-sized caterpillar hairs that are toxic to human skin get caught up in the wind and can cause health problems to nearly anyone near trees, especially oak trees. While a bad rash that’s similar in intensity to poison ivy is most common, some can suffer respiratory problems as well.

Dr. Bob Ritchie, 88, of Freeport, who lives on the coast and is surrounded by oak trees, says the rash has been impossible for him to avoid during the past several years.

“It’s a real bore. It’s a burning itch, and scratching doesn’t help. It’s really fierce,” said Ritchie, a retired physician. When he gets a particularly bad rash, he can’t sleep at night. None of the lotions and salves marketed by area pharmacies to ease the rash help, at least not for him.

“Nothing works for me, as best I can tell,” he said.

Frey said he can get the rash, too, so he takes precautions, such as when mowing fields at the state park wearing impermeable Tyvek suits that are often used by public health workers during infectious disease outbreaks.

Frey wears wide-brimmed hats during May and June so when the caterpillars fall on him, they are more likely to bounce off his hat than land down the front or back of his shirt.

He says anyone who detects a rash should wash it immediately with cold, soapy water.

“Don’t use hot water, as that opens up the pores and can make the rash worse,” Frey said.

The hairs can still be toxic even years later, so people raking leaves or gardening are at risk, even during the off-season.

Browntail moth infestations are cyclical, driven by weather conditions. Maine’s moth problem has gotten progressively worse during the past five years.

“A lot of these forest pests go through boom and bust cycles,” said Tom Schmeelk, a forest service entomologist. “We are currently in a boom cycle.”

He said it’s difficult to predict when the boom might end. The last major collapse was in 2004 and 2005 after extremely cool and wet springs.

The moth has no natural predators, but a naturally occurring fungus can infect the caterpillars, causing kill-offs after a particularly wet spring, especially if there’s a lot of damp, wet weather in May when the caterpillars emerge.

“If we get a wet April, the caterpillars are still protected very well in their webs,” said Eleanor Groden, an entomology professor at the University of Maine in Orono.

A hot, dry late summer, such as what has occurred in Maine the past two years, are perfect conditions for the moths, helping them survive and reproduce. So Groden said a wet spring may help temporarily reduce numbers, but if it’s followed by a dry summer, the moths can come roaring back.

“They thrive in the dry weather,” she said.

Research on new strategies to reduce the browntail moth population is in its early stages.

“We have a walk-in cooler (at UMaine) filled with caterpillars in their webs,” Groden said. “We are just beginning to understand the winter web integrity, the chemical structure of the webbing, and what makes them so strong.”

Groden said the idea is if a biological treatment can weaken the webs over the winter, the cold, windy days during wintertime could destroy enough webs to reduce the population.

Trimming trees is not practical on a widespread level because the trees are too tall.

A biologic pesticide, called BT (which infects the moths with the bacterium Bacillus thuringiensis) can be effective when sprayed, but widespread use is expensive. There are other biologic pesticides that also help control the problem for one season, but Groden said a more permanent solution hasn’t been found yet.

John Eldridge, Brunswick’s town manager, said the town and school department spray public areas, such as parks, recreation areas and near schools, but just doing that costs about $40,000. He said it’s effective in limited areas, but there needs to be a more comprehensive solution.

It’s unclear how effective aerial sprays would be, Eldridge said, and chemical pesticides are expensive and raise environmental concerns, such as damaging coastal waters and lobster habitat. Aerial spraying was common in coastal Maine in the 1990s, but the practice became increasingly controversial.

Schmeelk, the forest service entomologist, said the browntail moth caused similar problems through much of New England and even near New York City about 100 years ago. The populations collapsed in the 1920s, but the moths re-emerged in Maine in the 1990s and to a much smaller degree in Massachusetts.

Now the infestations are largely confined to Maine.

He said scientists don’t know why the moth has stayed primarily in Maine, but the reason may be related to the state’s unique coastal micro-climate. The combination of the browntail, gypsy and winter moths and dry weather are weakening oak trees along the Maine coast.

“If the oak trees are defoliated, it can really affect the health of the oaks. The oaks along the coast are suffering from numerous problems,” Schmeelk said.

Although it’s not clear yet whether the Legislature will approve the browntail moth research funding, Schmeelk said any efforts to boost research and collaboration among UMaine and the forest service will be welcomed.

“It’s a Maine problem,” he said. “If we don’t study this in Maine, nobody will.”