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.

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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When is the greatest risk of getting the rash? +

  • The greatest risk for exposure to the toxic hairs is between April and July.
  • Caterpillars, shed skins, and cocoons all have toxic hairs.
  • The toxin is stable in the environment for one to three years and hairs can become airborne at any time.
  • It is important to take precautions year-round in heavily infested areas.

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When do browntail moth adults fly? +

  • Adults emerge in July and are flying through August. Peak activity around lights at night is between 10 pm and 12 am.

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Do the browntail moths also have toxic hairs like the caterpillar? +

  • There is a possibility of adult moths picking up the toxic hairs from the caterpillar stage as the moths emerge from their cocoons; however, the brown hairs on the abdomen are not the toxic hairs.
  • The caterpillars, pupal cocoons, and shed skins have the toxic hairs that can cause a skin rash.
  • The hairs on the adult moths are not toxic and do not cause a skin rash.

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How can I get rid of browntail moth adults? +

  • A wet/dry vacuum with a HEPA filter and filled with a few inches of soapy water.
  • Keep outdoor lights off at night during the last week of June to the first week in August

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Does killing browntail moth adults (moths) help with management? +

  • Moths found on buildings and in light traps are primarily males. Killing males is unlikely to reduce the next generation of browntail moth.
  • Using a bug-zapper or other device to kill insects attracted to lights is not recommended. It will kill insects that might help control browntail moth and other pests as well as browntail moths. It will also attract more browntail moths to the area. Females attracted to an area by lights tend to hang out in host tree foliage and are not captured in high numbers with these methods.

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All Frequently Asked Questions


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News

Browntail Moth Update #12: August 16, 2024

Browntail caterpillars have emerged from their egg masses

Earlier this month, browntail moth caterpillars hatched from their egg masses and began chewing on their host leaves. At this life stage, the caterpillars are very small; only about a quarter inch in length. Newly hatched caterpillars are pale yellow in color, with a black head and two dark spots near their head (see photo below).

These young caterpillars will feed communally on host plants from now until the end of September or early October, depending on the weather. Damage from these caterpillars during this time of year is generally not a serious health issue for the plants. The browntail caterpillars will also start building their winter web for shelter through the coldest months, so you may start to see the formation of their winter webs.

Young browntail caterpillars hatch from an egg mass in Old Town, ME.
Young browntail caterpillars hatch from an egg mass in Old Town, ME.

Because of the browntail caterpillars' small size, their mouths are not large enough to consume entire leaves. Instead, they graze on the outer surface of the leaf, which causes the leaf to die and turn a bronze or copper color. This damage is called skeletonization. When we perform our aerial browntail moth surveys in the late summer, we look for this copper colored damage in the trees to help identify where browntail moth populations are severe.

Browntail caterpillars skeletonize oak leaves in Dedham, ME. Note the copper color of an older feeding site on the right side of the oak leaf.
Browntail caterpillars skeletonize oak leaves in Dedham, ME. Note the copper color of an older feeding site on the right side of the oak leaf.

Although it is much less common this time of year, exposure to hairs from previous seasons’ caterpillars can still cause skin irritation. These exposures often happen during activities that stir up hairs in the environment during dry conditions such as performing yardwork or closing camp. Caterpillar hair exposure can also happen through contact with old pupal cocoons which are often still attached to host foliage/ sheltered areas, or surfaces on which hairs settled that have not been washed clean. The caterpillars currently feeding on the leaves are unlikely to cause a reaction in most people.

Webs and small caterpillars in August: browntail or fall webworm?

Our native fall webworm (Hyphantria cunea) are often mistaken for browntail moth caterpillars. Both insects are active in August and these caterpillars can be found eating the same host plants, and creating filmy silken webs. So how can you tell the difference?

  1. (Carefully) Check the web!
    • The size of the web - oftentimes, fall webworm webs will be larger than browntail webs during late summer (see photo below).
    • The caterpillars on the web - if there are two dark spots toward the head of the caterpillar, these are likely browntail caterpillars. If these are not present, they are likely fall webworm caterpillars. Young browntail caterpillars also tend to be smaller (about a quarter of an inch) compared to fall webworm (often longer than a quarter of an inch).
  2. Are there silk 'highways'? In late summer, browntail caterpillars will build white silk highways to help them travel in their host trees. In trees with fall webworm, although there is silk, they do not create readily observed trails. Instead, fall webworm caterpillars create large webs that oftentimes take up many leaves and branches on a tree.
Webs created by fall webworm caterpillar, an insect native to Maine. These caterpillars do not cause rash in humans and are not a forest health issue. Fall webworm webs can get quite large, oftentimes taking up many leaves and branches in a tree. Browntail webs will not get this large - web size can be a good factor to determine which caterpillar is making webs on your property. Garland, ME.
Webs created by fall webworm caterpillar, an insect native to Maine. These caterpillars do not cause rash in humans and are not a forest health issue. Fall webworm webs can get quite large, oftentimes taking up many leaves and branches in a tree. Browntail webs will not get this large - web size can be a good factor to determine which caterpillar is making webs on your property. Garland, ME.

It's August and I think I have active browntail caterpillars on my trees. What can I do?

Management of browntail moth in the late summer is limited, as pesticide treatments may not be effective and web removal can be difficult with crawling caterpillars. Instead, monitor your trees for active winter web creation throughout the fall to better understand which trees may need pruning or treatments. If you're not sure if you have browntail moth webs or fall webworm, you can always give us a call or send us photos so we can help determine the insect making the webs.

Pesticide treatment of browntail caterpillars in the summer is not recommended and may not be effective. Treatment of the very young browntail caterpillars can be difficult for a few reasons:

  • Active skeletonizing of leaves from browntail in late summer can be difficult to detect and browntail are not always found on the same trees they defoliated in the spring (although this is possible in areas with high populations). If you can’t tell if there are newly hatched caterpillars in your trees, plan to observe them more closely over the winter and decide whether and how to treat them before spring. Please do not treat trees that do not have current signs of browntail (copper colored leaves from feeding).
  • Caterpillars produce silk and feed under it, therefore, pesticides sprayed on leaves and other non-systemic pesticides may not be as effective.
  • Trees in late summer may be less effective at absorbing and spreading trunk-injected pesticides throughout the tree’s leaves and therefore treatment may not be as effective.

We're looking for browntail caterpillar observations!

Browntail populations appear to be spotty compared to previous years. We are looking for your reports of hatched browntail caterpillars or browntail egg masses from this current season! Your observations will help us understand where browntail moth is most active in the state right now. Please send reports to foresthealth@maine.gov. If you can, attach a photo from your phone and let us know when and where you took the photo. This will make it easier for us to confirm identity and track where populations are being reported.

Have other questions about browntail moth? Check out our extensive FAQ page for additional information and resources!

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2023 Browntail Moth Awareness Month Webinar

Browntail Moth Mitigation Fund

The application period has now closed. The Division of Procurement Services Grant RFP/RFA page will have updates as soon as they are available. Please stay tuned for more updates.

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 2023 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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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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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.