Warning: browntail moth cocoons are full of the caterpillars' toxic hairs!

June 21, 2018

For more information, contact: Forest Health and Monitoring at (207) 827-1813

Browntail moth--an invasive species whose caterpillars have toxic, irritating hairs-is found at varying population densities over more than 6500 square miles of Maine (see map). It is a pest that has hunkered down in the Midcoast and Casco Bay area for years, and has recently expanded its footprint.

People looking to reduce browntail moth populations may look at the cocoons as an opportunity for reduction. However, you will have limited impact through cleaning cocoons. Safer, more effective control will be had through targeting larvae, either in overwintering webs (put a reminder in your calendar now to look for those structures at the tips of host branches around your property this fall and winter!) or as they feed on host leaves in early spring.

You may still want to remove the cocoons to limit potential for exposure to the toxic hairs they contain. However, do this with extreme caution. Cocoons are full of the hairs THAT CAN CAUSE A RASH or worse. If you plan to remove cocoons:

  • Wear protective clothing (in addition to long sleeves, pants, socks, socks, shoes, gloves, mask and glasses, consider protective coveralls)
  • Wet down cocoons before removing them
  • Scrape cocoons and drop them in soapy water, let them soak overnight then dispose of them

Even if you don't plan to remove cocoons, become familiar with their appearance, and learn to avoid them or wear appropriate protective clothing during your outdoor activities that might bring you in contact with them.

Browntail moth caterpillars wander and form their cocoons anywhere. Favorite places include: Under the eaves of buildings or the undersides of anything (reports include vehicles, and even a baby stroller) and wrapped in the leaves of any plant.

Traveling within the cocoons on vehicles, outdoor equipment and other items (including firewood), is a very efficient means of spread for this moth. If you have plans to travel between the affected and unaffected areas over the next month, check your belongings closely for these cocoons. This winter, be on the lookout for the tell-tale webs in new places. These are the places where control will be most effective!

Supporting documents

Large communal pupal masses on oak. Photo: Maine Forest Service, DACF

Browntail moth cocoon with several pupae in defoliated bur oak (Bangor, ME, June 20, 2018). Photo: Maine Forest Service, DACF.

Invasive browntail moth cocoon wrapped in invasive common buckthorn leaves beneath defoliated bur oak (Bangor, ME, June 20, 2018). Photo: Maine Forest Service, DACF. Photo: Maine Forest Service, DACF.