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 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? +

Browntail Moth adults do not have toxic hairs like the caterpillars do. However, they may have residual caterpillar hairs on their bodies. Pupal packets (cocoons) are full of toxic hairs. When the moths wiggle out of their cocoons, they may pick up some of the caterpillar hairs left behind from their previous life stage.

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How can I get rid of browntail moth adults? +

Put a HEPA filter into a wet/dry vacuum and fill the base of the vacuum with a few inches of soapy water. Vacuum the moths off the side of your house, porch, garage, or other surfaces. Leave them in the soapy water for a few days before disposing of the vacuum contents.

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Should I treat the small caterpillars that hatched in August? +

  • Using foliar or injectable pesticides to target the young caterpillars in late summer is very difficult and general not recommended by Maine Forest Service:
    • The skeletonizing of the leaves from the young caterpillars can be hard to see. When applying pesticides, label directions will instruct you to confirm the presence of the pest before application. Do not treat uninfested trees.
    • Browntail caterpillars produce silk and feed underneath it, therefore, pesticides sprayed on leaves or other non-systemic pesticides may not be as effective.
    • Trees in late summer may be less effective at absorbing and spreading injected pesticides throughout the tree's leaves and therefore may not be as effective.

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Is the state doing anything to help landowners/towns who have BTM? +

  • Currently, the state is:
    • supporting and conducting research,
    • tracking infestations,
    • supporting public nuisance declarations and
    • providing education to individuals, municipalities, businesses and others on response options.
  • LD 1929 from the 130 legislative session was signed on May 3, 2022. It allocates one-time funding of $150,000 to be distributed to government or non profit organizations for browntail moth response. Maine Forest Service is currently working with the approved organizations for this Browntail Moth Mitigation Fund. The Division of Procurement Services Grant RFP/RFA page will have updates as soon as they are available.

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All Frequently Asked Questions

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News

Browntail Moth Update #15: August 15, 2023

Browntail moth (BTM) egg masses across the state began hatching the week of August 7. 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 the beginning of October, depending on the weather. Damage this time of year is generally not a serious health issue for the plants. The BTM caterpillars will also start building their winter web for shelter through the coldest months.

Browntail moth caterpillars have emerged from their egg mass to construct silk webs and skeletonize leaves of their host tree. Old Town, ME.
Browntail moth caterpillars have emerged from their egg mass to construct silk webs and skeletonize leaves of their host tree. Old Town, ME.

As the young caterpillars feed, they graze on the outer surface of the leaf without consuming the entire leaf. This damage is called skeletonization and causes the leaf to die and turn a copper color. When we perform our aerial BTM surveys in the late summer, we use this damage to help identify where BTM populations are severe. We are starting to see some skeletonization damage visible from the ground, notably on I-95 in a stretch from Orono to Bangor and in Hampden and Etna. In these trees, leaves on the outer tips of the branches are a copper hue.

BTM caterpillar skeletonization damage; note the small caterpillars in the upper center of the photo.
BTM caterpillar skeletonization damage; note the small caterpillars in the upper center of the photo.

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 now feeding on the leaves are unlikely to cause a reaction in most people.

Summer treatment of the very young browntail caterpillars can be difficult for a few reasons:

  • The leaf skeletonization damage from the younger caterpillars can be difficult to detect.
  • Caterpillars in late summer are not necessarily 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 uninfested trees.
  • Caterpillars produce silk and feed under it, therefore, pesticides sprayed on leaves or other non-systemic pesticides may not be as effective.
  • Trees in late summer may be less effective at absorbing and spreading injected pesticides throughout the tree’s leaves and therefore treatment may not be as effective.

Small caterpillars in August: Browntail or Fall Webworm?

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

  1. (Carefully) Check the web! Oftentimes, fall webworm webs will be larger than browntail webs during late summer.
  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.
  3. Look at the caterpillars! If you can safely reach the area where the caterpillars are, check for two dark spots toward the head of the caterpillar, if present, these are browntail caterpillars. If not present, they are 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).

Browntail Moth Videos


If you are still struggling to identify the caterpillars, you can wait until later this fall, when the small winter webs of the browntail moth are formed. At that time, the silk highways engineered by browntail caterpillars (see photo below) are well developed and the caterpillars will wrap one or more leaves together to create their recognizable winter web. Webs of fall webworm will break down through fall and winter, as they are no longer in use by their creators.

In late fall, browntail caterpillars create silk 'highways' that let them travel in their host trees. Webs of fall webworm will break down through fall and winter and will not be as visible as browntail silk structures.
In late fall, browntail caterpillars create silk 'highways' that let them travel in their host trees. Webs of fall webworm will break down through fall and winter and will not be as visible as browntail silk structures.

Exposure to these young browntail caterpillars are unlikely to cause a reaction in most people, however, personal protection is still recommended. The toxic hairs from the previous seasons' caterpillars are still stable in the environment, therefore, caution should be taken to avoid stirring up the hairs that have settled in areas near past infestations.

Will you have Browntail Moths flying in your area?

Adult browntail moths emerge in July and are flying through August. 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 general idea of where browntail moth is in Maine from our interactive map, updated with 2023 winter web surveys. To understand what browntail moth is up to near you in August, take a look at host plants for fuzzy egg masses, emergence of small browntail caterpillars and skeletonization of leaves.

Browntail Moth Interactive Map

Browntail FAQ Page

What else is chewing my trees?

Examples of caterpillars that are similar to browntail moth. They are Eastern Tent, Forest Test and Spongy Moth.

Eastern tent caterpillars are native to Maine and are abundant throughout the state. To identify these insects, look for a solid white stripe down the center of their back and blue spots that resemble the "eye" in peacock feathers. The good news is this is not a forest pest. It is often considered an aesthetic pest or a concern for plants where fruit production is a goal. This caterpillar feeds on Rosaceae hosts (apples, pears, cherries, serviceberries, hawthorns, and others) and creates a silken tent after hatching from eggs in the spring.

We have received reports and observed defoliation caused by forest tent caterpillars in northern Maine. These caterpillars are native to Maine and can be recognized by the off-white "keyhole" or "footprint" shaped markings on their back. Aspen tends to be the target host in northern Maine; however, these caterpillars can feed on many hardwood species. Most recently, this insect contributed to the death of a mature oak stand in Blue Hill, ME.

Spongy moth caterpillars are an invasive species and have been spotted in many counties of Maine. These hairy caterpillars have prominent knobs on each side of their head, and older caterpillars will have five pairs of blue spots, followed by six pairs of red spots on their back. Like browntail, it has two orange glands toward the rear of the caterpillar, however, spongy moth caterpillars do not have the toxic hairs that browntail have. Because the state experiences different climates, spongy moth caterpillars in some areas are still young and have not yet developed their characteristic blue and red spots yet. These caterpillars develop later in the season and are generally smaller than others (browntail, forest tent, eastern tent) at this time of year. Spongy moth and browntail moth are vulnerable to the similar fungal and viral diseases. We hope the rainy weather will contribute to fungal disease activity especially in spongy moth caterpillars since they are still early in their development. 

The not-so-hairy winter moth caterpillars are wrapping up feeding in coastal Maine and have denuded hardwood trees in many areas where they are found. These invasive caterpillars are typically pale green with a faint white stripe running down both sides of its back. Around this time of year, you may find them dangling out of their host trees (oak, maple, ash, apple and other fruit trees) using a silk thread to find additional food or move into the soil below to pupate into moths. Pupae remain in the soil through late fall and can be moved with soil from infested areas. It appears this is a primary way this pest is spread to new areas. 

Finally, we have received numerous reports of leaf damage. Frost has hit many tree species quite hard in some portions of the state. This type of damage appears as a wilt symptom to many, but some mistake it for insect feeding.

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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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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.