Browntail Moth Update #5: May 29, 2025
This week at our monitoring sites, we observed browntail caterpillars continuing to grow and defoliate their host trees. At our Old Town site, we noticed the presence of spongy moth caterpillars (Lymantria dispar) with browntail caterpillars. Similarly to browntail moth, spongy moth is also an invasive species found in Maine. Although their active period overlaps with browntail caterpillars, they are much smaller at this time of year - see photo below comparison.
Image: A side-by-side comparison of a spongy moth caterpillar (left) next to a browntail moth caterpillar (right) in Old Town in late May. Spongy moth caterpillars have distinct "knobs" on each side of their head that develop before their pairs of colored spots.
Which caterpillar is eating my trees?
In late spring, there are many caterpillar species enjoying Maine's trees. While most caterpillars go unnoticed, their presence is made known when they start to defoliate your trees.
The chart below shows three of the most common species that often get misidentified as browntail moth caterpillars: eastern tent caterpillars, forest tent caterpillars, and spongy moth caterpillars.
 All these caterpillars are hairy, but only browntail caterpillars have hairs with irritating toxins that can cause a rash. Some people are sensitive to the hairs of any caterpillar, so picking up hairy caterpillars is generally not recommended.
Larger browntail caterpillars may start to wander to new trees in search for fresh leaves, but sometimes, they can end up on your car, house, decks, lawn equipment, or elsewhere.
Avoid parking under areas with browntail caterpillars. Check tree branches that may overhang your car or truck when choosing a parking spot to avoid taking them home with you.
Image: Browntail caterpillars on a branch overhanging the bed of a truck in late May.
If you have browntail caterpillars crawling on your house or car:
- Use a strong jet of water to knock them off
- Use a wet/dry vacuum with a few inches of soapy water and a HEPA filter, then let them soak for several days
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