Browntail Moth
Euproctis chrysorrhoea (L.)

Browntail Moth Update

September 10, 2021

Thank you for your reports, we’ve received observations of heavy damage from the young caterpillars from North Yarmouth to Sidney. Feeding damage from the young caterpillars is very apparent in many areas especially in Kennebec county. Let us know where you are seeing damage.

Nearly completed winter web with skeletonization damage in the background, Augusta ME
Nearly completed winter web with skeletonization damage in the background, Augusta ME

These small caterpillars will feed now through the end of the month or longer if it is a warmer, milder fall. As they feed, they graze on the outer surface of the leaf without consuming the entire leaf. This type of damage is called skeletonization and causes the leaf to die and turn a bronzy-copperish color. When we perform surveys for BTM in the late summer/early fall we use this damage to aide us in mapping where BTM populations are high.

Skeletonization damage on oaks, Augusta Maine
Skeletonization damage on oaks, Augusta Maine

There is a small window to treat BTM in the late summer/early fall, however treatment of the very young caterpillars can be difficult for a few reasons:

  • The skeletonization damage from the young caterpillars is sometimes difficult to detect since they are not defoliating the trees like they do when larger caterpillars.
  • Caterpillars are not necessarily found on the same trees that were defoliated previously in the season, although in high populations it is possible.
  • If using injections, the uptake of the pesticide by the tree may not be as effective as spring treatments, especially if using a passive non pressurized system.

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. 


Is summer 2021 expected to be a particularly bad year for browntail moth encounters?

Generally speaking, this year will be as bad or worse than last year in terms of potential encounters with browntail moth. Browntail moth populations in Maine have been in an outbreak phase since 2015, and populations last year continued to increase. In particular, the dry spring of 2020 limited disease in the caterpillar stage allowing a bumper crop of moths to disperse in July.

What areas of Maine are most at risk?

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. Highest populations, as reflected by mapped damage by aerial survey, are found in Androscoggin, Cumberland, Kennebec, Knox, Lincoln, Sagadahoc and Waldo Counties.

What areas are at risk this year that were not heavily infested in the past years?

Our aerial survey data points to increased impacts in parts of Cumberland, Kennebec, Knox and Waldo County, with late-summer damage mapped in areas where early summer defoliation was not seen. Our winter web surveys point to continued spread of the pest up the Penobscot River and I-95 corridors and in southern portions of Oxford, Franklin Somerset and Penobscot Counties. More disjunct sightings occurred in three towns in Aroostook County (Fort Fairfield, Monticello and Smyrna). Other areas where BTM was prevalent last year have spread to varying extents.

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

Consulting this year’s winter web 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 prior to overwintering

Where is the best resource to find how to protect oneself from 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.

  • 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


Maine 211 - Get Connected. Get Answers.For More Information:
Dial: 211 or 866-811-5695
Text Zip Code to 898-211
Email: info@211maine.org


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. 

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)