The fall webworm, or tentworm, is particularly evident this year, which given its abundance, consider it an outbreak. Not to worry. The webbed nests cover treetops throughout Northwest Arkansas now. These “tents” are the home of the larval stage of an otherwise inconspicuous white moth Hyphantria cunea. This species is found throughout much of the United States and Canada, extending into northern Mexico. It is also an invasive alien in China, first seen in 1979, and even considered an aesthetic threat to the 2008 Beijing Olympics. It landed in Yugoslavia in the 1940s and is invasive in most of Europe.
Egg-laying from the nearly pure white fuzzy adult females, with a wingspan of about 1.25 inches, begins in May or June. Females can lay upwards of 500 eggs, covered in white hairs on the underside of leaves. It is usually the second-generation larvae that we see this time of year. Once the larvae hatch, they begin spinning the web, which expands with the growing brood of larvae and helps to protect them from predators.
The webs or tents are usually on the ends of branches on the host tree on which the larvae feed. Many trees in our area are affected including black walnuts, elms, hickories persimmons, sycamores and other species. They have been recorded on over 100 tree species, especially broadleaf deciduous trees, rarely on conifers.
The larvae can damage young persimmon or pecan trees. On other trees, the unsightly infestation rarely consumes enough foliage to actually damage the trees. Don’t confuse the fall webworm with the eastern tent caterpillar which is seen in the crotches of trees in spring. The fall webworm will stay within its protective tent and continue to munch on leaves until they’ve had their fill, then transform into the pupal stage and the cocoons over-winter in leaf litter.
Although we may have a visceral reaction to their presence which initiates our urge to get rid of them, relax and wait it out, because in most instances, it’s a visual annoyance to humans, not an actual threat to the vast majority of trees where the fall tentworms make their home. There’s really no need to do more than tolerate the unsightly presence of these insects. The most harm they will do is to your sense of aesthetics, plus they are a good reminder that winter is coming.