Experts: Fall Webworms Harmless To Trees


September 7, 2017

Ray Adams

Webworms can be seen all over the county, including on North Country Club Road.

Every fall the webworms come back, but this year, in particular, it seems like they are everywhere. In the Western North Carolina region, they favor trees like sourwood and sweet gum, but can be found on nearly any kind of hardwood tree this time of the year.

Big picture, the worms are not harmful, according to Bart Renner with the N.C. Cooperative Extension office in Transylvania County.

"They're very common," said Renner. "Last year, everybody was saying they're bad because it's dry. This year it's because it's wet. We don't know why conclusively, but we do know that they are worse this year. They come around this time every year, and the main thing we need folks to understand is that generally the fall webworm is not going to kill your tree. Cosmetically, it's not attractive, so that's the issue for some folks. They notice these big webs and they want to get rid of them."

Renner said he had read some suggestions on the "We are Brevard" Facebook page to spray them with insecticide or even burn them out of the trees.

"That's not real smart," he said. "The inherit risk of insecticides is not worth the result that you're going to get. The insecticides are not effective against them. They have the protective web and it really keeps them safe, and spraying a poisonous material above your head and have it raining down on you is just not a good idea. By burning them out you might get rid of the forest too."

If you really just can't stand the site of webworms in your tree, cut the branch out of the tree or take a stick and open the web up, which will make the webworms accessible to birds and other animals, Renner said.

Dr. Jill Sidebottom, with the College of Natural Resources at N.C. State University, is a trained entomologist with an office at the Mountain Horticultural Crops and Extension center in Mills River. While Sidebottom mostly works with evergreen trees, she does recognize how much bad information is circulating around the webworm, "Especially when they are exposing themselves to hazardous materials," she said.

"They're just a pest that happens about every fall," she said. "It's really nothing to worry about. The best thing to do, if you just have to do it, is to take a stick and break it open, and birds will get in there and eat them."

Sidebottom said that the worms take all year long to develop, and lay their eggs on the underside of leaves.

Hyphantria cunea, the fall webworm, is a cousin to, and often confused for, the eastern tent caterpillar that spins webs in the crotches of trees rather than the ends of branches. An inch or so long, the yellow and brown caterpillars spend the larval stage of their life eating the leaves inside the web, which takes about six weeks of their life cycle.

In the pupa stage of their life, the caterpillars cocoon at the base of trees in the bark or in the leaves that have dropped in the fall. The adult moth is mostly white, and in the spring the moth emerges from the cocoon, mates and can lay up to 900 eggs on the underside of one leaf.

Other suggestions for controlling the number of fall webworms on your property include the use of dormant oil, which is used in the early spring while the trees are still dormant. Most garden stores supply dormant oil, and it is the least toxic of the many different methods used to control the caterpillars.

Fall webworms occur throughout most of North America, Japan and Korea. In the southern part of North America, the moths are whiter, while further south the moths are dotted with black and brown.

Ray Adams

The webworms do no harm to the trees.


Powered by ROAR Online Publication Software from Lions Light Corporation
© Copyright 2017