HARPSWELL — After months of studying the local browntail moth population, a professor of entomology from the University of Maine said caterpillars treated in the lab are surviving longer than she’d hoped.

Dr. Eleanor Groden gave selectmen an update on the study, which Town Meeting voted to fund last March, at their regular meeting Oct. 4.

The browntail moth is an invasive species that presents both forest and human health concerns. The caterpillars feed on hardwood trees and shrubs, and adverse health reactions in humans can be triggered by the insect’s fine hairs, which can cause a rash and breathing issues. 

As part of the study, researchers brought foliage from trees treated around Harpswell back to the lab and fed it to caterpillars to see if they died.

Groden said because the treatment used includes “biological materials,” they are temperature dependent just like insects’ physiology, which is why researchers wanted to test results in the lab under controlled temperatures.

“We don’t want to jump to conclusions about what happened in the field at this point; we were hoping we would see lower survival of the caterpillars fed in the lab,” she said. “That said, they were taken care of in the lab, so under more stressful conditions maybe they would’ve succumbed to mortality. Once we get all of our data analyzed we’ll be able to say what happened in the field.”


Groden said she and student researchers still have a lot of information and samples to process and she recently hired five undergraduate students to assist.

Voters opted to give just over $9,500 towards the work after Groden presented to selectmen at a workshop last November. She is director of the university’s Browntail Moth Research Project, which is conducted in collaboration with the Maine Forest Service.

Groden and her team will continue to monitor winter webs around Harpswell through February 2019, and give a final presentation when their research is complete.

The college’s project aims to pinpoint the cause of the insect’s spread throughout the state, as well as eco-friendly ways to squelch it.

Groden told the board last week she and her students visited approximately 20 sites around town this spring to sample the infestation and then identified places they would follow up with over the summer.

The options they used to treat the moth habitats are less toxic than traditional insecticides; Harpswell’s pesticide ordinance prohibits spraying within 25 feet of the shoreline. It also bans aerial spraying.


Groden told board members most of what her team works with is certified organic and only lasts about 12 hours after being sprayed. The treatment also breaks down in UV light and generally only impacts insects.

One of the eco-friendly options used was a naturally occurring fungal pathogen in some moth populations which multiplies and kills larvae in the nest when the weather is favorable. Another was a bacteria; Groden said both options used together reduced caterpillar survival more effectively than either method used alone.

In the field, she said she noticed “very little wintering mortality” of the nests at any of the sites that were sampled. In early May the researchers applied treatments on three occasions, depending on the emergence of caterpillars from their winter webs. 

Two weeks later, they came back to see how many of the caterpillars were still alive and continued returning.

In the fall, Groden said they assessed how many small larvae were feeding at each of the sites, as well as how many webs were at each site.

In addition to the treatments made in Harpswell, she said researchers also had two other locations in the Mid-Coast where they administered multiple doses of the treatment.


Groden said she hopes to have more concrete results to share by the end of the year.

She also said she has been in contact with a scientist from New York who is working on a different study involving browntail moths, and she is supplying him with “as many critters as he wants” for his work, which could eventually also help the Harpswell research. 

“It’s a lot of data and samples that we’re still trying to work our way through,” she said. “But hopefully by the end of the year … we’ll get it worked up and we’ll be able to give you more definitive results at that time.”

Elizabeth Clemente can be reached at 781-3661 ext. 100 or eclemente@theforecaster.net. Follow Elizabeth on Twitter @epclemente

Researchers from the University of Maine will continue their research into Harpswell’s browntail moth population this winter after receiving more than $9,500 for the effort from the town. 

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