Browntail Moth
Euproctis chrysorrhoea (L.)

Browntail Moth Update

September 30, 2021

Caterpillar feeding activity seems to be slowing down as the winter webs are basically complete in many areas of Maine where they occur. The pathogen affecting the young caterpillars we noted in the last update is fairly widespread on the state campus here in Augusta with most trees that were inspected having at least some webs with deceased caterpillars on them. If you are seeing similarly deceased caterpillars send us an email. During this visual inspection we also noticed some flies in the family Tachinidae investigating the webs. The larvae of this family of flies are exclusively parasitic on arthropods of all shapes and sizes. There are a few species of tachinid fly that use browntail caterpillars as a host, good news for us and the flies, bad news for browntail. This past season we have been bringing you updates on development as they happen and with a decrease in caterpillar activity, we will likely change from a weekly update to more of a monthly update.

Tachinid fly on browntail moth winter web. Augusta, Maine.

Tachinid fly on browntail moth winter web. Augusta, Maine.

If you are noticing a lot of damage from browntail moth on your property now, it is not too early to plan your response to reduce impacts next year. Plan to remove webs within reach once the trees are dormant. Communicate with your neighbors in case they are not aware of the problem. If you have a lot of webs out of reach from the ground, you may want to contract with a licensed pesticide applicator for treatment or a licensed arborist (PDF) for web removal and destruction. Consider working with your neighbors to manage this pest. 

What do we know about 2022 browntail populations?

We have scant details about 2022 browntail populations, but we do have an idea of what to expect. Generally speaking, we expect conditions to be as bad or worse than last year in terms of potential encounters with browntail moth and their hairs. Browntail moth populations in Maine have been in an outbreak phase since 2015, and populations continued to increase in 2021, with more than 180,000 acres of damage mapped in early summer aerial surveys. Also, the second consecutive dry spring in 2021 limited disease in the caterpillar stage, allowing a bumper crop of moths to disperse in July 2021. We will know more about the 2022 outlook after late-summer aerial surveys and 2021-2022 winter web surveys.

What are areas of Maine that are most at risk for 2022?

Most areas of Maine, especially along the coast and inland, that have significant host tree populations are at risk. In 2021 overwintering browntail moth webs were found in every county in Maine except York. The highest populations in 2021 were found in Androscoggin, Cumberland, Kennebec, Knox, Lincoln, Sagadahoc, and Waldo Counties, with some pockets of high populations in adjacent counties. Aerial surveys for 2021 will wrap up in September, and data on mapped spring and late-summer damage will be made available to help gauge risk for the coming year.

What are the most precise ways for people to know the browntail moth situation in their area?

Consulting the most current survey map will give people a general idea of what the BTM population looks like in their area. However, there is no substitute for inspecting the host trees and shrubs around places they frequent.

  • Late-fall through early spring: on sunny days, examine hosts for winter webs on the tips of host branches
  • Spring-early summer: look for the distinctive caterpillars. The white stripes characteristic of older larvae usually develop in late May. The two orange dots towards the rear are present throughout this stage.
  • Early summer through leaf fall, watch for and avoid cocoons and their remnants.
  • Late-summer watch for distinctive feeding and developing silk created by young caterpillars before overwintering

Since toxic hairs haven’t been produced since the end of June in 2021, do I still need to be concerned about exposure?

In areas with low browntail moth populations and individuals who are not highly sensitive to the toxins in the browntail caterpillar hairs, the risk of a reaction is reduced. This is in part because the risk of encounters with the hairs is reduced with ample rainfall after spring-feeding caterpillar activity has stopped. Consistent rain has been seen over much of the infested areas from July and into September; this will help incorporate hairs into the soil and reduce their chance of becoming airborne in drier conditions. However, sensitive individuals and people in areas with moderate to high populations in spring 2021 or prior should continue to use caution in conducting work that might stir up the hairs or otherwise lead to encounters with them. Activities such as sweeping, raking, mowing, using leaf blowers, gardening, handling firewood or other material where hairs may have settled or caterpillars may have pupated are examples of conditions that may lead to encounters with the hairs long after the caterpillars are gone. 

Where is the best resource to find how to protect oneself from and manage browntail moth?

More Frequently Asked Questions

  • Close up of overwintering webs of browntail moth in northern red oak (Maine Forest Service Photo, April 2018)

    Close up of overwintering webs of browntail moth in northern red oak.

  • Close up of overwintering webs of browntail moth in ornamental crabapple (Maine Forest Service Photo, February 2017)

    Close up of overwintering webs of browntail moth in ornamental crabapple

  • Caterpillar of browntail moth (Maine Forest Service Photo, May 26, 2016)

    Caterpillar of browntail moth

  • Communal cocoon of browntail moth in an ornamental crabapple (Maine Forest Service Photo, June 20, 2016)

    Communal cocoon of browntail moth in an ornamental crabapple

  • Communal cocoons of browntail moth (Maine Forest Service Photos)

    Communal cocoons of browntail moth

  • Adult browntail moths (Maine Forest Service Photos, July 15, 2016)

    Adult browntail moths

  • Browntail moth eggs and adult (Bath Forestry Division Photo, July 17, 2017)

    Browntail moth eggs and adult

  • Late-summer browntail moth larvae and webs (Maine Forest Service Photos)

    Late-summer browntail moth larvae and webs

  • Browntail moth overwintering webs (Maine Forest Service Photos)

    Browntail moth overwintering webs

General Information

The browntail moth is an insect of forest and human health concern which was accidently introduced into Somerville, Massachusetts from Europe in 1897. By 1913, the insect had spread to all of the New England states and New Brunswick and Nova Scotia. Since that time, populations of this pest slowly decreased due to natural controls until the 1960's, when browntail moth was limited to Cape Cod and a few islands off the Maine coast in Casco Bay. Browntail moth populations are again building in Maine and are found in patches along the coast and up to 60 miles inland from the western Maine border to the New Brunswick border, with the greatest concentrations in mid-coastal Maine and the capitol region.

The larval stage (caterpillar) of this insect feeds on the foliage of hardwood trees and shrubs including: oak, shadbush, apple, cherry, beach plum, and rugosa rose. Larval feeding causes reduction of growth and occasional mortality of valued trees and shrubs.

While feeding damage may cause some concern, the primary impact on humans by browntail moth results from contact with poisonous hairs produced by the caterpillars. Microscopic, toxic hairs break off the caterpillars and can be airborne or settled on surfaces in browntail moth infested areas. Sensitive individuals who encounter the hairs may develop a skin rash similar to poison ivy and/or trouble breathing. Symptoms can last anywhere from a few hours to several weeks and can be severe in some individuals.

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Background Information

Research

Entomologists with the Maine Forest Service in the Department of Agriculture, Conservation and Forestry (DACF) have teamed up with the University of Maine to track the spread and investigate the causes of the outbreak and evaluate management strategies for this daunting pest. Read the report on Browntail Moth Research at the University of Maine.

Survey & Management Resources

Maine Forest Service conducts surveys for browntail moth from small planes and from moving trucks. These are broad-scale surveys that do not completely cover the entirety of the impacted area. To understand what is happening in your neighborhood, and whether you are at risk of exposure to browntail moth, learn to recognize browntail moth then inspect the trees around you. The best time of year to do this is in the winter from mid-December through March. Browntail moth is most recognizable at this stage and management can occur or be lined up ahead of the spring season. 

Browntail Moth Dashboard interactive map

Aerial Detection Survey Maps

Winter Web Survey Maps

Citizen Science Survey Protocol

Businesses that manage browntail moth

Video on Removing Browntail Caterpillar Nests

Use extreme caution if burning webs. Never burn unless the branches have been clipped off. This type of burning requires a burn permit. For more information, please visit www.maineburnpermit.com and check the daily forest fire danger report.

Removing Browntail Caterpillar Nests from Jeff Fischer on Vimeo.
2021 Browntail Moth Winter Web Moth Survey (PDF | 640 KB)