James Stewart, a lab manager at the University of Maine, and graduate student Emma Irvine collect nests of browntail moth caterpillar pupae from an oak tree on the UMaine campus in Orono on June 26. Gregory Rec/Staff Photographer

ORONO — Wearing white protective suits designed for handling hazardous materials, students at the University of Maine gather nests filled with the pupae of browntail moths from an oak tree on campus.

Students Tucker Wile, Emma Irvine and Ru McClung, and lab manager James Stewart use a clipper attached to a pole to gingerly cut down 60 nests the size of tennis balls on a recent day, carefully sealing them in plastic bags.

Ru McClung, an undergraduate student at the University of Maine, cuts leaves away from a nest of browntail moth caterpillar pupae collected from an oak tree on the UMaine campus on June 26. Gregory Rec/Staff Photographer

Once back in the university’s lab, the students and their professor hope the nests will help them find a way to fight back against the invasive insects that have tormented people across much of the state by shedding microscopic hairs that cause red, itchy rashes.

“These nests are basically a pinata of toxins,” said Angela Mech, an assistant professor of forest entomology at the University of Maine.

Mech’s research is investigating whether it’s possible to disrupt the mating patterns of the browntail moth as a way to curtail populations and limit the range of the forest pests.

So far, Mech’s team has landed $325,000 in grants to test whether dispersing a synthetically made product designed to mimic the sex pheromones of the female browntail moth can confuse enough male moths to drastically reduce their ability to reproduce. The pheromones would either be sprayed or dispersed over large areas.


The goal of the university researchers is to find out how to drive down the browntail moth population in an environmentally friendly way.

Mech sums up the mission in six words: “Save our trees. Save our skin.”

A live browntail moth caterpillar in a sealed plastic specimen cup. Angela Mech, assistant professor of Forest Entomology at the University of Maine, is studying how to disrupt the mating patterns of browntail moths, which if successful, could help to control populations and infestations of the invasive pests. Gregory Rec/Staff Photographer

Every spring, microscopic hairs from the caterpillars drift through the air and land on thousands of Maine people, causing red, itchy rashes and, in some cases, breathing problems.

This image from a scanning electron microscope shows a single hair of a browntail moth caterpillar magnified 1,000 times. The hairs are hollow and contain a toxin that is released when it punctures a person’s skin. Courtesy of Sadia Crosby/UMaine

The state is in the eighth year of an outbreak and the impacts have become more acute as the browntail moth’s range expands to cover much of Maine. Scientists suspect climate change is contributing to the proliferation of the moths.

Spikes found on the tiny caterpillar hairs pierce the skin and release toxins that cause the rash.

The caterpillars shed hairs every time they are startled, and also when they molt, which is about six times during their short lifetime in the spring.


In some people, the rash can cause sleep-disrupting itchiness that lasts weeks. Breathing in the hairs also can cause respiratory problems.

For browntail moth researchers, the rash is almost unavoidable.

By late June, almost all of the caterpillars are in pupae and no longer shedding hairs. But touching nests can nevertheless bring on rashes, so the students try to steer clear of the microscopic hairs by avoiding being downwind from the caterpillars and wearing protective gear that includes hazmat suits, goggles and gloves.

“You can’t have any exposed skin, not even the part between the gloves and the sleeves,” said Emma Irvine, a master’s degree student.

The students will clip 750 nests from various oak, crabapple and cherry trees as one of the first steps in the research process.

Once the nests are brought to the lab, researchers deposit the pupae into tiny plastic containers, similar to ketchup containers sometimes used at fast food restaurants.


By mid-July, thousands of moths will emerge from the pupae and the researchers will immediately separate the moths by sex – the females can be identified by their bulkier abdomens – so they can use them for a variety of experiments and educational purposes.

Angela Mech, assistant professor of Forest Entomology at the University of Maine and a team of students are researching browntail moths to see if their mating patterns can be disrupted to reduce infestations, which are expanding across the state. Gregory Rec/Staff Photographer


One experiment – designed by Irvine – will determine how far a female moth can fly. Devin Rowe, a doctoral environmental science and entomology student, built a structure where the moths are attached to a flying treadmill-like device to calculate the flying abilities of female moths compared to males.

“The hypothesis is she doesn’t fly very well. We’ll find out soon,” Mech said.

How far the female moth can fly would help scientists determine how large of an area would need to be treated, assuming the pheromones work as hoped and confuse the males.

“We don’t want the females to be able to simply fly out of the sprayed area,” Mech said.


Mech said the experiments and research will ultimately determine whether the pheromone strategy will work, but they are hopeful because a similar tactic was used to curtail spongy moth populations in the Midwest. The spongy moth is an invasive species that has caused massive defoliation and is found in 20 states, including Maine. It is not a public health nuisance like the browntail moth. The browntail moth also can cause defoliation and harm the health of trees, such as oak and fruit trees, but it is not quite as harmful to trees as the spongy moth.

“The browntail moth and the spongy moth are closely related, so we have reason to believe this will work,” Mech said. “It would be a very targeted biologic pest control, very specific to browntail moths, so it would not harm any other species.”

In North America, the browntail moth is found in large numbers only in Maine and Cape Cod, although there have been reports of the moth in Canada.

In a lab at Deering Hall on the University of Maine campus, Mech’s team set up about 20 large plastic tubs for future experiments. The tubs, equipped with a fan and an exhaust so the air doesn’t stagnate, will each contain a mason jar. Female moths will be in some of the mason jars, as will a lure that looks like a pencil eraser sprayed with the synthetic pheromone to mimic the females.

Devin Rowe, a Ph.D student at the University of Maine, explains how a team of students plans to use the modified storage bins at right to see if a synthesized female browntail moth pheremone might disrupt a male moth’s ability to locate the female. Gregory Rec/Staff Photographer


A single male moth will be placed in each tub and scientists will be looking to see how well the synthetic pheromone confuses the males. If the males in the tubs containing the lures can’t find the females in the mason jars, that means the synthetic pheromone is working.


Female browntail moth specimens are displayed in a box made by Angela Mech, assistant professor of forest entomology at the University of Maine. Gregory Rec/Staff Photographer

“The more we learn about the mating behaviors of the browntail moth, the more we can target our response to be more effective in the field,” Mech said.

The moths only live for roughly 10 days, so many experiments will be concentrated in a short window of time.

If the experiments prove to be effective, the next step would be taking the pheromone product out in the field to test how well it works. Mech said there are promising models from spongy moth spraying done in the Midwest.

“One method is it would be sprayed from airplanes, and it would look like tiny droplets of toothpaste, that stick to leaves and are biodegradable,” Mech said.

Rowe also will be setting up 35 pheromone traps in various Maine locations that will help determine the range and projected hot spots for the browntail moths each year. The Maine Forest Service currently conducts surveys of winter webs, but it’s time-consuming work, and Howe said the traps could eventually be a more efficient way to count moth populations.

Browntail moths recently extended their range from coastal and central Maine to the Orono region, and have only been prevalent on the University of Maine campus the past two years. But they have quickly taken over, infesting about half of the campus’ 800 trees, including many of the towering oaks.

“They have a large buffet of trees to choose from,” Mech said. She pointed to cherry and crabapple trees that have been almost completely defoliated by the caterpillars, while other healthy trees have lush green leaves.

While unsightly, the browntail moth’s presence on campus has made research more convenient, and Rowe said he enjoys exploring new frontiers of study.

“It’s exciting because no one’s really studied this, so it’s like a whole open sea we are researching,” he said.

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