This YouTube video was posted last year by someone who got a rash from exposure to browntail moth hairs.

Browntail moths, those pesky insects whose hair can cause a range of allergic reactions, is continuing its trek through Maine and leaving a trail of rashes and respiratory troubles in its wake.

Now in its end-stage caterpillar form, the pests are munching on tender leaves of apple, oak and other trees. If you spot them in your yard – they have two telltale red dots on their back ends – stay away. The microscopic hairs they shed can be toxic for up to three years. Reactions to the hair range from mild rashes to something similar to poison ivy to trouble breathing.

“By the time June arrives, the caterpillars are in the last stage of feeding. They have shed their skin four times already and have one more to go,” said Charlene Donahue, a state entomologist who studies the browntail moth.

With each shedding, the density of new hair builds up and with it, their toxicity. The tiny hairs (0.15 millimeters) can become airborne, landing in places where they can potentially come in contact with humans, such as trees, lawns, decks and picnic tables.

The hairs are a double threat: they contain a toxin, which causes a chemical reaction with some people, and the hairs are barbed, which causes physical irritation.

“If someone has a severe allergic reaction, it’s not something to fool around about,” said Donahue. “People should take precautions and seek medical help.”

The hairs are most abundant from May through July when the caterpillars are in a feeding frenzy before they change into moths in August.

RELIEF AND CONTROL

According to the Maine Department of Agriculture, Conservation and Forestry, the moths are continuing to spread from their hub in Sagadahoc County, where they first appeared in 2008. While the risk remains high along the coast from Cumberland to Wiscasset, the moths are now moving into new territory Down East and onto islands east of Rockland and Belfast to Deer Isle.

Donahue said the infestation is worse this year than last based on the numbers of web nests. In addition to heading Down East, it seems some are starting to move inland to places like Monmouth and Turner. Donahue said it’s entirely possible that hairs can be embedded onto vehicles, and then unwittingly distributed to areas where there are no nests.

The nests are easy to spot. Caterpillars build them in the fall on the tips of branches, where they spend the winter. The state offers tips on how and when to prune trees to remove the nests so that the caterpillar never develop into moths, which lay eggs for the next generation. But this late in the year, there’s really nothing to do to control an infestation, said Donahue.

The best advice is to protect yourself from exposure, by limiting time outdoors, especially on windy days when the hairs can be swirling in air currents.

If you do encounter the irritating hairs, there are some over-the-counter medications that can treat a mild to moderate rash. Some people get relief from taking an antihistamine, or using hydrocortisone cream or calamine lotion for the itching and rashes.

Compounding pharmacies in Portland and Augusta make their own versions of browntail moth treatments available with a prescription.

Joe Lorello, registered pharmacist at Coastal Pharmacy and Wellness in Portland, said people often come seeking quick relief from a browntail moth rash. The pharmacy offers a spray and cream version of its formula.

“They frequently decide on the spray form since the rash is often painful to touch,” he said.

Kennebec Pharmacy, which has retail branches in Brunswick and Rockport, also makes its own browntail moth treatment, available by prescription. Last year the pharmacy filled more than 850 prescriptions to treat rashes and swelling from exposure to the browntail moth hairs, according to general manager Joe McVety.

If you are having symptoms related to exposure to browntail moths, the Northern New England Poison Center, at 1-800-222-1222, can help you determine whether you need to see a doctor, pharmacist or go to the emergency room.