All About Browntail Moth Caterpillars (BTM)

by Marissa Caminiti, UMaine Extension Administrative Specialist, Cumberland County

What BTM’s Are & What You Can Do:

Last week at the UMaine Extension Cumberland County office, we noticed a few caterpillar nest tents in the branches of the crab apples. The caterpillars had just begun to hatch. We removed them by cutting the nests out of the trees.
It is important that even if you are not able to determine the species of caterpillars, you will still want to use extreme care when removing the nest and use appropriate protection equipment, especially gloves.
To cut the nests out of trees: use pruners and place the nests directly into a bucket of soapy water. Allow the nests to sit in the soapy water for several hours, then the nests may be discarded. This removal method is an alternative to using pesticides, especially for small-scale problems and especially in environmentally sensitive areas.

What are Browntail Moths?

Browntail Moth caterpillars (BTM) are a common invasive species of caterpillar which affects the health of Maine’s forests and people. This species of caterpillar has toxic hairs that can cause a skin rash. This risk map of heavily infested areas shows where in Maine BTM’s are known to be: Browntail Moth locations (PDF)

Close up of pruners clipping a caterpillar nest out of a crabapple tree.
Pruning the caterpillar nest out of the crab apple tree.
Pruners holding a crabapple branch with a caterpillar nest on it, and dipping it into a bucket of soapy water.
Disposing of the caterpillar nest while wearing proper protective clothing.
Caterpillar nests are in a bucket of dishsoap and water.
Soaking caterpillar nest in a bucket of soapy water for several hours.
The life cycle and pest treatment plan of a Browntail moth. September through April, survey, clip, and destroy winter webs. Line up insecticide treatment. before June, treat feeding larvae with insecticide. Take personal protection precautions. June and July have the highest risk for hairs, at the pupae stage. July  through August, adult stage. Limit outdoor lights, as it attracts moth to lay eggs, which happens from July through August. In August through September, feeding larvae hatch, use insecticide treatment. Toxins in hairs last 3 years or longer. Exposure more likely in dry conditions. In infested areas, use personal protective precautions whenever conducting activities that might stir up hairs.
Maine Department of Agriculture, Conservation, & ForestryMaine Department of Agriculture, Conservation, & Forestry

What can the general public do about BTM’s?

  1. Report your detection of BTM in this survey to the Maine Forest Service if this is an area outside of where the BTM is already known to be widespread.
  2. Make a donation to support UMaine Browntail Moth research. As it is difficult to fund research for BTM, any contributions are greatly appreciated!
    Donations can be mailed to:
    THE UNIVERSITY OF MAINE FOUNDATION,
    TWO ALUMNI PLACE,
    ORONO, ME 04469-5792
    (Please specify that funds are specifically for support of the University of Maine Browntail Moth Project.)

FMI about BTM’s, review these links: