Browntail Moth - Euproctis chrysorrhoea (L.)

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Frequently Asked Questions

Partners at Maine Forest Service, Maine Board of Pesticides Control, Maine Center for Disease Control, Cooperative Extension and others have put together an extensive list of frequently asked questions. Questions cover topics from biology, to management, to policy to pets.

When will the caterpillars be active? +

  • The caterpillars are active at two times of the year. In mid-April, they emerge from their winter webs and begin feeding and growing until they reach their maximum size in June.
  • The second batch of caterpillars hatch from their eggs in August and are active until early October when they enter their winter webs to hibernate, emerging the following spring.

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What time of year am I most likely to get a rash from the browntail moth caterpillar? +

  • The greatest risk for exposure to the toxic caterpillar hairs is between April and July.
  • Caterpillars, shed skins, and pupal cocoons all have toxic hairs that can cause a skin rash.
  • The toxin is stable in the environment for 1-3 years and hairs can become airborne if disturbed, so one should take precautions year-round in heavily infested areas.

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How can I get rid of caterpillars? +

  • Learn to recognize and avoid skin contact with caterpillars. A key feature is two orange dots on the tail end.
  • Use a wet/dry vacuum with a HEPA filter filled with a few inches of soapy water to remove caterpillars on the side of your house.
  • Pesticides can be used to control caterpillars. The Maine Forest Service recommends contracting with a licensed pesticide applicator to control browntail moth. Products must be labeled for the site of treatment.
  • Pesticide treatments should be done before the end of May. Later treatments will not reduce human exposures to the toxic hairs.
  • Here is a list of contractors willing to do browntail work

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What is the optimal time for tree injections to treat browntail moth caterpillars? +

  • The optimal timing for control of the caterpillars is when they are small.
  • Injections that leave larger dead caterpillars with the associated hairs in your yard, either due to timing of injection or rate of product movement to leaves, are not ideal. In most years, controlling caterpillars before late-May is recommended.
  • Timing of injection may depend upon product used, tree species, mode of pollination, seasonal development, and injection system. The Department of Agriculture Conservation and Forestry recommends working with an experienced and reputable licensed pesticide applicator for management of this pest.
  • In any case, the label directions and other pesticide regulations must be followed. In addition, understanding of details regarding rate of translocation of the product to areas where the caterpillars are feeding and duration of product in leaf tissues and other parts is needed for optimal management.
  • If a homeowner is intending to conduct treatments on their own they should be sure to understand and follow the label and know that information beyond what is on the label may be needed to understand what product best fits their needs.
  • The product manufacturer, University of Maine Cooperative Extension Pest Management Office and Maine Forest Service Forest Health and Monitoring Division can provide additional guidance.
  • Read more on managing browntail moth in tall trees (PDF)

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How do I avoid exposure to the browntail moth toxic hairs? +

  • When working in heavily infested areas, wear proper protective equipment to reduce exposure including:
    • Long sleeves
    • Long pants
    • Goggles
    • Dust mask/respirator
    • Hat
    • Disposable coveralls
  • Avoid heavily infested areas between April and August, don't use leaf blowers or lawnmowers on dry days in these areas
  • Using pre-contact poison ivy wipes can help minimize hairs sticking into exposed skin
  • Do yardwork on wet days, which decreases the likelihood that the hairs will become airborne.
  • Make sure to use a HEPA filter on a wet/dry vacuum to decrease the likelihood that the hairs will become airborne.
  • Do not dry laundry outside in infested areas.

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Will there be additional funding for browntail moth mitigation activities for residents and towns? +

  • Unfortunately, there are no grant opportunities through the state for browntail moth mitigation activities at this time. In 2022, a one-time funding opportunity was created and made available to towns and non-profit organizations with moderate to high levels of browntail moth to help applicants reduce the impacts of browntail through education, mechanical, and chemical control.

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All Frequently Asked Questions


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News

Browntail Moth Update #3: May 16, 2025

Despite the rain and chilly mornings this past week in Maine, browntail caterpillars are still thriving thanks to the functional structure of their webs. These new thread-like expansions are made from silk, which is water repellent and helps keep the caterpillars dry during our rainy spring seasons.

Browntail caterpillars at some monitoring sites are developing faster than those at other sites. The largest caterpillars were at our monitoring site in Brewer, with a body length of about 0.58 inches (14.89 mm), while caterpillars at other sites were roughly 20% smaller. This pattern has happened in previous years and is likely linked to local weather differences between the sites.

Image: Browntail caterpillars continue growing and expanding their winter webs in Old Town. Note the bud damage from caterpillar feeding.
Image: Browntail caterpillars continue growing and expanding their winter webs in Old Town. Note the bud damage from caterpillar feeding.

Some of the larger browntail caterpillars at the Brewer monitoring site had developed broken white stripes down their back, indicative of the caterpillar nearing later instars (life stages). These more mature caterpillars will begin to make excursions from their host trees, leading to more encounters.

Additionally, as caterpillars eat and grow, they need to shed their outer skin, a process called molting. The number of toxic hairs in the environment increases with each caterpillar molt. Please take caution while performing outdoor yardwork near trees that have browntail caterpillars to avoid contracting a rash from the toxic hairs - wear long sleeves, eye protection, and gloves.

Image: Comparison of different browntail moth caterpillar instars. Fourth instar larvae have broken white stripes down their back, whereas third instar and younger do not have these markings.
Image: Comparison of different browntail moth caterpillar instars. Fourth instar larvae have broken white stripes down their back, whereas third instar and younger do not have these markings.

FAQ: Is it too late to remove browntail winter webs from my trees?

Yes, it is too late to remove browntail winter webs. The caterpillars have already emerged and begun eating foliage, so removing their webs now will not remove most of them and instead poses a risk to you contracting a rash and a risk to the tree from pruning stress.

Instead, consider treatments for trees with browntail caterpillars close to your house or in your dooryard to prevent most impacts. If treatment isn't an option, plan ahead to prevent the rash: avoid the areas when possible and cover up if you can't avoid the area.

FAQ: Is it too late to treat my trees for browntail caterpillars?

No, it is not too late, but time is running out - treat trees with browntail caterpillars before the end of May. Treatments after May are not as effective because the caterpillars will already have molted several times and eaten most (or all) of the leaves, both impacts that treatments aim to avoid.


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General Information

Adult browntail moth white with brown abdomenThe 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 capital 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. Learn More: How to Identify Maine’s Main Defoliating Caterpillars (YouTube) / Life Cycle of Browntail Moth (PDF)

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. Learn More: Maine CDC Browntail Moth Information

Management Techniques

Focus management on populations that will directly impact people, pets and livestock or pose a high risk of contributing to spread.

For Smaller Trees & Shrubs +

Browntail web removal: Webs in small trees and shrubs, safely within reach of the ground, and without hazards such as powerlines, can be removed between October and March. Browntail caterpillars emerge from their webs and begin feeding in mid-April, therefore webs removed after this time will not contain caterpillars and not be effective. Destroy webs once removed (burn, soak for an extended period in soapy water, or dispose of in trash). With permission, you can do this on properties you don’t own or manage. If there are hazards, or you need to leave the ground, this is work for a licensed arborist.

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.

Browntail caterpillar treatment: Pesticide applications are most effective for browntail caterpillars when the pesticide product can take effect before late May. Treatments after that time are not recommended and are not part of an effective integrated approach to management (or IPM strategy). Since caterpillars are already wandering to new locations, targeted applications are not possible. Further, pesticide applications at this time of year are more likely to impact other living species in your trees, including pollinators and native insects, without effectively reducing the impacts from browntail. At this time, there are many shed caterpillar skins and toxic hairs that have already built up in the environment. To have more effective control of browntail, plan to target the next generation of caterpillars by scouting out new winter webs this winter to determine which trees you may want to treat next spring

Applications must be consistent with the label directions. Consider hiring a licensed pesticide applicator. In most years, treatment should be effective (caterpillars killed) before late May. Later treatments do little to reduce both hairs in the environment and damage to hosts.

If you are managing browntail moth using pesticides within 250 feet of the mean high tide mark adjacent to coastal waters and extending upriver or upstream to the first bridge, additional rules apply.

If you are unlicensed, do not use this approach on properties that are not yours or are open to the public.

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For Webs in Taller Trees +

Hire professional help to treat webs out of reach or near hazards on the property you own or manage. Line up help during fall or winter.

Licensed Professional Arborists can remove BTM webs in larger trees and shrubs (October to March).

Arborist pruning browntail moth webs.

Unmanned Aerial Vehicle (UAV) Operators with an FAA Remote Pilot License may provide services using UAVs with attachments that physically remove webs.There is no requirement that these operators have knowledge of tree care. As in working with any professional, confirm your prospective contractor is adequately insured and qualified to provide the service.

For large trees, there are very limited insecticidal products (PDF) that are readily available to and applied by unlicensed individuals and that can legally be applied to target trees and life stages of browntail moth.** In trees where the caterpillars' hairs cause a nuisance and where it is not practical to remove the webs, Licensed Pesticide Applicators may be able to use insecticides during the growing season to manage BTM.

**Acecaps are not registered for use in Maine because the label does not meet federal standards for pesticide labeling. It is therefore not legal to use Acecaps. The Maine Board of Pesticides Control has provided support to the manufacturer to explain what needs to be changed to come into compliance and encouraged the manufacturer to work with EPA to bring their label up to standards. If we become aware of a change in status, we will update this message. You can check the current registration status by entering the product name in this database.**

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Where is Browntail Moth in Maine?

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 impacted area. You can get a broad idea of where browntail moth is in Maine from our interactive map, just updated with 2025 winter web surveys. To understand what browntail moth is up to in a specific area, take a look at host plants for webs and signs of caterpillar activity.

Browntail Moth Interactive Map

Citizen Science Survey Protocol

Aerial Detection Survey Maps +

Winter Web Survey Maps +

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For Towns and Organizations

Pruning browntail moth webs.

Focus management on populations that will directly impact people, pets and livestock or pose a high risk of contributing to spread.

Hire professional help to treat webs out of reach or near hazards on the property you own or manage. Line up help during fall or winter.

Social Media Toolkit +

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Got questions about browntail moth? 211 is there to answer them.

Know your enemy and your friends. #KnockOutBTM, not silkmoths.

Image credits: DACF except promethea larva BOMONA user Zelenaks, promethea adult BOMANA user JRTindall

 

Learn how you can #KnockOutBTM and reduce the itch at www.maine.gov/dacf/knockoutbtm.

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Learn how you can  #KnockOutBTM and reduce the itch at www.maine.gov/dacf/knockoutbtm.

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Learn how to safely remove and destroy browntail moth winter webs from the Maine Department of Agriculture, Conservation and Forestry at www.maine.gov/dacf/knockoutbtm  #KnockOutBTM

To avoid encounters with the fuzzy caterpillars, remove and destroy browntail moth webs by April. Learn how from the Maine Department of Agriculture, Conservation and Forestry at www.maine.gov/dacf/knockoutbtm  #KnockOutBTM

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#KnockOutBrowntail Business Challenge +

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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.