Masses of webbing on the ends of tree branches in your yard and along the roadsides are the work of the fall webworm, a species of caterpillar native to our region. Fall webworm outbreaks occur every year in our area and are most noticeable in late summer and fall. This year they are particularly prolific, but fortunately they cause little lasting damage to trees and shrubs.
Where do they come from?
Fall webworms are native to much of
What will they eat?
Fall webworms are not picky eaters and have one of the widest host ranges of any insect. They are capable of feeding on just about any deciduous tree species. In our region, sweet gum, persimmon, and pecan are favorites. This year fall webworms have been noticed in higher numbers and on a wider range of trees than usual, including dogwood, wax myrtle, redbud, and bald cypress.
The mass of webbing spun by fall webworms is known as a nest. Each nest can contain hundreds of webworms, which hatched from an egg mass laid by a female fall webworm moth. The caterpillars in a nest feed together for several weeks, expanding the web as needed. Nests can reach three feet across or more. Fall webworms feed within their nest until they reach full size, at which time they crawl out of the nest, and usually away from the tree, to form a cocoon. You may find individual webworms on your deck, porch, driveway or plants. They are not seeking more food; just a place to spend the winter.
Will they hurt my tree?
While the webbing and debris created by fall webworms looks alarming, their feeding activity rarely causes serious injury to trees. Webworms only damage tree leaves and do not kill the branches upon which their nests form. These branches will grow new leaves next year so there is no need to cut branches out of a tree to remove the nests, which will naturally weather away during winter months.
Established trees can tolerate losing a considerable amount of foliage, particularly in late summer and fall. The injury caused by fall webworm feeding is considered cosmetic, only affecting the appearance of the tree, not the tree’s health. In most cases there is no need to do anything about fall webworms. The exception is young, recently planted trees which can be completely defoliated by webworms. In these situations it is usually beneficial to treat or physically remove webworms before significant leaf loss occurs.
What can be done?
Fall webworms have many natural enemies, including spiders, birds, and parasitic insects. Pulling webs open with a stick exposes the caterpillars to predators and will help reduce their numbers. Nests can be removed by pruning out the branch upon which they are found, but first check to make sure caterpillars are still active in the nest.
In the case of young trees that are in danger of being completely defoliated, insecticides can be sprayed on the leaves to control this insect. Any product labeled to control caterpillars will work. Products containing neem oil, B.t., or spinosad are organic options. When treating, first check if caterpillars are still present in the webs. Often, by the time nests are noticed the caterpillars have already left, making treatment unnecessary and ineffective. If caterpillars can be seen inside the webbing, target treatment to the foliage directly adjacent to the nest. There is no need to spray the entire tree. Because most insecticides are highly toxic to bees, wait until late evening to spray when bees have returned to their hive. Never spray when bees are active in the area.
For assistance identifying and managing plant pests, visit http://ces.ncsu.edu, where you can post your questions via the ‘Ask an Expert’ link, or contact your local Extension office. If you live in
Charlotte D. Glen is the horticulture agent with the Pender County Cooperative Extension of NC State University, College of Agriculture & Life Sciences. She can be reached via e-mail at Charlotte_Glen@ncsu.edu.