Browntail Moth Update #11: August 29, 2025
In August, browntail moth caterpillars hatch from their egg masses and begin feeding on the late summer host foliage. This year, we’ve had some trouble tracking down browntail moth egg masses to monitor their development. Browntail egg masses can be difficult to spot, but they are typically found on the underside of oak, apple, cherry, elm, birch and other hardwood host leaves.
Although there are still pockets of high browntail moth populations statewide, you may need to wait until later in the fall, after winter webs tighten up, to get a good understanding of what browntail impact may be next spring.
Browntail moth egg mass on the underside of a host leaf in Old Town, ME.
These newly emerged browntail caterpillars are too small to eat all parts of the late summer leaves, so they graze only the outer surface, leaving behind the leaf skeleton. Over time, this process of skeletonization causes the leaf to die and turn a copper color – a clue we use to identify browntail feeding in late summer. However, the native fall webworm, slug sawflies, and other can cause similar looking symptoms in host trees.
Identification of caterpillars is not critical this time of year because late summer management for browntail moth caterpillars is not recommended. It can be difficult to find egg masses – by the time the caterpillars have eaten enough foliage to cause leaf death, it is often too late for foliage applications to be effective. Damage from browntail moth caterpillars at this time of year is generally not severe or disruptive to the tree and there is limited production of toxic hairs. The best management practices include waiting until the winter season to survey and remove browntail winter webs from your trees. If winter web removal is not feasible, winter is a good time to line up insecticide treatments for trees in high traffic areas.
As we transition from summer into the autumn season, fallen leaves may harbor toxic browntail moth hairs. See the FAQ below for tips to avoid exposure during fall clean up activities.
Does the web:
- Engulf entire branches, or sometimes the whole tree?
- Have larger (>1" long), hairy, yellowish-green bodied caterpillars crawling on it?
--> Friend! You are likely looking at our native fall webworm (Hyphantria cunea) caterpillars. These caterpillars are not a forest health concern and do not cause a rash in humans, although their webs can be unsightly in trees until they break down in the winter season. Fall webworm is having a banner summer and you can see the evidence of its success enveloping hardwoods across the state. Celebrate their success and leave them be with the knowledge that, as Wagner (2005) describes in his excellent Caterpillars of Eastern North American guide, they are "parasitoid hotels."
Fall webworm caterpillars can make large webs in late summer, but they do not have toxic hairs like browntail moth. Their webs can get large, but will break down over the winter season.
But, if the web:
- Is only the size of your palm,
- Has silken pathways leading up the branch,
- Has small pale yellow caterpillars with a black head and two dark spots near its head,
--> Foe! You are likely looking at browntail moth caterpillars. Management is not recommended in the late summer because it is not effective, however, monitor these webs and remove them in the winter season to reduce browntail moth populations on your property.
Young browntail moth caterpillars are pale yellow and have dark spots near their black head.
If you've had browntail moth caterpillars on your property in the last 3 years, you may still have hairs in your yard that can cause a rash - especially during fall cleanup when leaf blowing, raking, and mowing are frequent. These activities can stir up the toxic hairs, so here's what you can do:
- Wear proper protective gear to reduce exposure: long sleeves, long pants, socks and closed-toed shoes. Goggles and a mask may also be helpful.
- Preform yardwork on wet days, or early in the morning to decrease the likelihood that the hairs will become airborne.
- Shower after being outside to rinse off any hairs that may have settled on your skin
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