The picture is from Jeff Burbrink’s backyard. Pictured are fall webworm feeding on cherry leaves. In the evening, when the threat of birds has passed, the larva crawl out of the web and envelop more leaves. They feed on the leaves during the daylight hours under the protection from the webs. This web has doubled in size over the past week. Photo provided by Jeff Burbrink.

By Jeff Burbrink
Ag & Natural Resources Extension Educator, Purdue Extension LaGrange County

LAGRANGE — You may have noticed webs growing on some trees around the county. The creature responsible for this webbing is the fall webworm. I have been watching one web in a cherry tree on my property. In the past week, it has doubled in size as the larva inside the web grow and consume more foliage. Purdue has a publication on them.

Jeff Burbrink

As the season progresses, these webs will grow in size, sometimes covering entire trees. The webs may be ugly, but the feeding rarely has serious consequences to the health of the tree.

Fall webworms only eat what is inside the webs, so as the caterpillars grow in size, so do the nests. Their preferred trees are walnut and cherry, but I have seen them on many species this month, including oak, apple, maple and locust trees.

Looking inside the webs, you will see skeletonized or brown leaves. This sometimes scares people because they fear their tree will die from the feeding. In actuality, this late season feeding has very little effect on the tree. Most trees have already packed away enough nutrients to survive until spring, and the feeding is of little consequence. In fact, they are reducing the number of leaves you need to rake.

If you feel you must control fall webworms, please do not try to burn the nests. Over the years, numerous people in our community have burned themselves by building torches. Gasoline explodes when fumes come in contact with flames. Burning the webs does lasting damage to the branches on the tree, whereas the feeding does no harm at all.

Insecticides are rarely needed either. The exception may be newly planted trees (if they are heavily infested) and fruit trees, which require a continual flow of carbohydrates to support fruit expansion. It is important to remember that insecticides will not remove the unsightly nest.

Another reason to avoid using insecticides is their potential negative impact on critters that feed on fall webworms. There are over 80 species of insect predators and parasites known to make a meal of fall webworms.

A simple way to reduce their numbers is to disrupt the web, if the nest is close to the ground. Use a stick to knock around the web, which opens it up to larger predators such as birds and squirrels. It will not completely wipe out the nest, but should reduce the overall size.

As I have repeatedly said, the defoliation from fall webworm may be unsightly, but it is of little consequence to the tree. I would be much more concerned about eastern tent caterpillar, which building webs in the crotched of tree branches in the spring, and the spongy moth (formerly known as Gypsy Moth), which defoliate trees in the spring, and force the tree to expend energy to regrow leaves during the summer.

You can read more about tent caterpillars at extension.entm.purdue.edu/publications/HN-83.pdf and spongy moth at extension.entm.purdue.edu/publications/GM-1.pdf