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Browntail Moth

Euproctis chrysorrhoea[11]

The browntail moth is an invasive moth whose caterpillars and cocoons carry toxic hairs that cause skin rashes and, if breathed in, breathing problems. The National Park Service calls it a pest of both human and forest health; Maine has had outbreaks for about a decade.[2][1][9]

Group
Insect
Order
Lepidoptera
Family
Erebidae
US records
3 states
Sources
11 cited
Updated
2026-11-11
Browntail moth caterpillar, dark and hairy with rows of orange markings, on a leaf
Browntail moth caterpillar, dark and hairy with rows of orange markings, on a leaf. (c) Drepanostoma, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Where it lives
  9. Where sources disagree
  10. Other stinging caterpillars
  11. Common questions
  12. Sources

How to identify it

  • Grown caterpillars are about 1.5 inches long, dark brown with white stripes and covered in barbed hairs. Two bright red-orange spots near the rear tell them apart from similar caterpillars.[2]
  • Winter webs are 2 to 4 inches long, a tightly wrapped leaf bound in bright white silk at the tip of a branch, often on apple or red oak. Each holds 25 to 400 young caterpillars.[1]
  • Females lay eggs in masses of 200 to 400 on the undersides of leaves and cover them with hairs from their bodies.[1]

Look-alikes

Look-alikeHow to tell them apart
Fall webwormFall webworm webs start around a few leaves and grow to envelop whole branches, filling with leaf bits, shed skins and droppings, and the caterpillars feed inside. Browntail winter webs are small, single tightly wrapped leaves in white silk at branch tips.[3][1]

Where it lives

Brought from Europe and discovered in the eastern U.S. in 1897, it spread across New England, then collapsed to relict coastal populations on outer Cape Cod and Maine's Casco Bay islands. It resurged in Maine in 1989 and has been at outbreak levels there since 2015 or 2016, depending on the source.[5][4][2]

US map: public records from 3 states since 1990 (GBIF).

Biology and life cycle

Eggs hatch around August and September. The young caterpillars feed briefly, then build winter webs at branch tips and spend the winter inside in groups.[1]

As leaves open in spring, usually by April, the caterpillars leave their webs to feed. They are full grown around June and spin cocoons, which are also full of the irritating hairs.[1]

Adult moths emerge in July. UMass says the adults do not typically cause skin rashes.[1]

Wet springs help a fungus disease, Entomophaga aulicae, sweep through populations; warm late summers and falls let more caterpillars survive the winter. Fall temperatures have been rising in Maine since the moth's resurgence.[4][2]

Hosts include oak, apple, cherry, beach plum, rugosa rose and shadbush, and in Acadia National Park also birch, serviceberry and alder.[1][2]

Damage and signs

  • Caterpillars defoliate many deciduous trees and shrubs, but UMass says that may be secondary to the public health concern.[1]
  • Researchers in Maine describe outbreaks over the past several years on a scale not seen in the northeastern U.S. in over 100 years, leaving homeowners and land managers with very low tolerance for the pest.[7][4]

Health risk

Contact with the hairs causes caterpillar dermatitis, an itchy rash, and MedlinePlus lists eye irritation, breathing trouble if hairs are inhaled and, rarely, severe allergic reactions among the effects of caterpillar hairs. Remove hairs from skin with sticky tape, wash with soap and water, flush eyes with plenty of water and get medical help, and call Poison Help at 1-800-222-1222 with questions.[9][8]

Control

Prevention

Avoid places infested with the caterpillars, especially from April through July when exposure risk is greatest. Wear gloves, long sleeves, long pants and closed-toed shoes when working near any caterpillar or cocoon, and wash exposed skin and clothing afterward.[2][1]

Traps and physical control

Clip winter webs from branch tips in fall or winter, before leaves open and the caterpillars start feeding, then drop them in soapy water or destroy them. Winter is when exposure risk is lowest, which is why Acadia National Park removes its webs then.[1][2]

Biological control

A fungus disease, a virus, tachinid flies including Compsilura concinnata, and parasitic wasps all attack it. That same fly, introduced in 1906 against spongy moth, likely drove browntail moth out of most of its former range.[1][6]

Pesticides

In a Maine field trial on caterpillars coming out of their winter webs, Bacillus thuringiensis kurstaki (Btk), Beauveria bassiana and azadirachtin all reduced caterpillar numbers, but only two applications of Btk, or a Btk plus Beauveria tank mix, cut the number of pupal nests.[7]

UMass lists many other active ingredients for landscape use, and asks that sprays go on after bloom to protect pollinators. In Massachusetts, neonicotinoids have been state restricted-use on trees and shrubs since July 1, 2022.[1]

Where it lives

It was discovered in the eastern U.S. in 1897 and spread until about 1914, covering about 150,000 square kilometers at its peak. By the 1960s it survived only on outer Cape Cod and on islands in Maine's Casco Bay.[5][4]

It resurged in Maine in 1989. In Massachusetts it has recently been confined to parts of Cape Cod and the North Shore, mostly on beach plum.[4][1]

Coastal sites suit it better than inland ones: overwintering death was lower on the coast in Maine and Massachusetts studies.[5]

GBIF's US records since 1990 come from three states, Maine, Massachusetts and New Hampshire, the great majority from Maine.[10]

Where sources disagree

When the Maine outbreak began: Maine researchers date the dramatic increase to 2016, as does UMass (roughly 2016), while the National Park Service says Maine populations have been at outbreak levels since 2015.[4][1][2]

Risk season: the National Park Service says exposure risk is greatest from April to July, while UMass says it rises between May and July but hairs can be a problem at any time of year.[2][1]

Why it vanished from most of New England: one study implicates the parasitic fly Compsilura concinnata, while a later study found cold inland winters affect the moth but cannot explain both its rapid spread and its collapse.[6][5]

Common questions

Do browntail moth adults cause a rash?
Not typically. The caterpillars and cocoons carry the toxic hairs, which cause the rash.[1][9]
How do I tell browntail webs from fall webworm webs?
Browntail winter webs are small, 2 to 4 inches, tightly wrapped single leaves in white silk at branch tips, seen from fall into spring. Fall webworm webs grow to envelop whole branch ends and fill with leaf bits and droppings.[1][3]
What should I do if I get the rash?
Pull hairs off the skin with sticky tape, wash with soap and water, and apply ice wrapped in a cloth. Flush eyes with water and get medical help if hairs got in your eyes or you breathed them in.[8]

Sources

  1. UMass Extension Landscape, Nursery and Urban Forestry Program, “Euproctis chrysorrhoea (Browntail Moth), Insect & Mite Guide.” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/euproctis-chrysorrhoea (accessed 2026-11-11)
  2. U.S. National Park Service, “Browntail Moth in Acadia: 2025 Management Update.” www.nps.gov/articles/000/browntail-moth-in-acadia.htm (accessed 2026-11-11)
  3. UMass Extension Landscape, Nursery and Urban Forestry Program, “Hyphantria cunea (Fall Webworm), Insect & Mite Guide.” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/hyphantria-cunea (accessed 2026-11-11)
  4. Environmental Entomology, via PubMed, “Factors influencing the population fluctuations of Euproctis chrysorrhoea in Maine (Boyd et al. 2021).” pubmed.ncbi.nlm.nih.gov/34175937/ (accessed 2026-11-11)
  5. Environmental Entomology, via PubMed, “Factors influencing larval survival of the invasive browntail moth in relict North American populations (Elkinton et al. 2008).” pubmed.ncbi.nlm.nih.gov/19161686/ (accessed 2026-11-11)
  6. Ecology, via PubMed, “Implicating an introduced generalist parasitoid in the invasive browntail moth's enigmatic demise (Elkinton et al. 2006).” pubmed.ncbi.nlm.nih.gov/17089674/ (accessed 2026-11-11)
  7. Journal of Economic Entomology, via PubMed, “Evaluation of biorational insecticides for management of Euproctis chrysorrhoea (Groden et al. 2022).” pubmed.ncbi.nlm.nih.gov/36201287/ (accessed 2026-11-11)
  8. MedlinePlus, U.S. National Library of Medicine, “Caterpillars (Medical Encyclopedia).” medlineplus.gov/ency/article/002860.htm (accessed 2026-11-11)
  9. Dermatologica, via PubMed, “Dermatitis caused by the larva of the brown-tail moth, Euproctis chrysorrhoea L. (de Jong 1977).” pubmed.ncbi.nlm.nih.gov/863075/ (accessed 2026-11-11)
  10. Global Biodiversity Information Facility (GBIF), “Euproctis chrysorrhoea: US occurrence records since 1990 by state (GBIF occurrence search API).” api.gbif.org/v1/occurrence/search?taxonKey=1821856&country=US&hasGeospatialIssue=false&occurrenceStatus=PRESENT&year=1990%2C2026&facet=stateProvince&facetLimit=400&limit=0 (accessed 2026-11-11)
  11. iNaturalist, “Euproctis chrysorrhoea taxon page (order and family).” www.inaturalist.org/taxa/337520 (accessed 2026-11-11)

Updated 2026-11-11. Built from sourced records. Spot an error? Tell us.