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 should I clip overwintering webs? +

  • The Maine Forest Service recommends clipping webs between October and mid-April before caterpillars emerge from winter webs and begin feeding on new leaves.
  • This task is more easily accomplished after the leaves have fallen from the trees as the webs are more visible.

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How do I determine if I have a high browntail moth population and what should I do? +

  • Conduct a population assessment to determine how many webs are in the trees on your property. This should happen as early as possible in the dormant season beginning in October; however, it is often difficult to spot webs in oaks until December. A guide to surveying for webs is available online here www.maine.gov/dacf/mfs/forest_health/documents/browntail_moth_citizen_science_survey.pdf
  • Contractors (licensed pesticide applicators or arborists) should be lined up as soon as a decision is made to contract for help.
  • Web clipping should happen during the dormant season, generally October through Mid-April
  • Caterpillar treatments should happen in early spring, generally before the end of May.
  • The best time to manage browntail moth is when its populations are low.

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All Frequently Asked Questions


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News

Browntail Moth Update #13: September 4, 2024

What insect is eating my trees?

In late summer, there are many insects defoliating leaves of their host trees. Fortunately, there are clues we can look for to help us differentiate the insects causing minor damage in our trees. Here’s another look at how to tell the difference between late-summer webs of the harmless fall webworm and the notorious browntail moth.

Browntail moth webs vs. fall webworm webs

Browntail moth caterpillars skeletonize leaves and begin creating a web using silk on the leaf remains. A strong silk holdfast will tie the webbed leaves to the twig, Bangor, ME (left). Fall webworm caterpillars chew on leaves and continue expanding their web with silk, Old Town, ME (right). Note the size difference between the two webs.
Browntail moth caterpillars skeletonize leaves and begin creating a web using silk on the leaf remains. A strong silk holdfast will tie the webbed leaves to the twig, Bangor, ME (left). Fall webworm caterpillars chew on leaves and continue expanding their web with silk, Old Town, ME (right). Note the size difference between the two webs.

In early September, browntail moth caterpillars will continue skeletonizing leaves, causing the leaves to die and turn bronze. The silk on browntail webs is very minimal at this time, with fine, gauzy silk covering some leaves and thicker, thread-like trails along the twigs and connecting leaves to twigs.

As we approach autumn, browntail caterpillars will continue covering skeletonized leaves with ever-thicker white silk, building their winter hibernacula. When the weather gets colder, the caterpillars will become dormant and remain inside their webs throughout the winter. These webs are easiest to spot in the winter once the rest of the leaves fall because they will look like leaves left on the trees. Silk wrappings shining in the sun will give away their true nature.

Fall webworm webs are much larger than browntail webs in early September, with more obvious silk webbing that spans a few branches and multiple leaves. Dead leaves can be seen inside of fall webworm webs. Once the fall webworm caterpillars mature, they will leave their webs and make their way into the soil beneath their host trees where they will pupate. Since they overwinter in the soil and not their web, they do not use their web anymore and the web will break down naturally.

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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.