Webworm nests arriving;damage is mostly cosmetic

Nancy Olsen

A sure sign that fall is just around the corner will be the fall webworm nests in trees such as pecans, sourwoods, persimmon and willows which are the preferred trees in this area.

The fall webworm, a species of caterpillar native to our region, are most noticeable in the late summer and fall with outbreaks occurring every year. The good news is fall webworms rarely cause serious damage and in most cases there is no reason to control them.

The caterpillars that feed on trees in our area are hatched from eggs laid by adult fall webworm moths, which are snow white and approximately 1 ½ inches long. These caterpillars will feed four to six weeks, then leave the host tree to spin a cocoon in the ground, where they will spend the winter.

Next spring adult moths will emerge from these cocoons and mate, after which the females will lay eggs, beginning the cycle all over again.

Fall webworms are sometimes confused with Eastern tent caterpillars, which only occur in the spring and are most common on wild cherry trees. Eastern tent caterpillars form their webs near the trunk of the tree, usually where a branch meets the trunk. Fall webworm webs are formed at the ends of branches and do not appear until late summer.

Fall webworms are also sometimes incorrectly referred to as bagworms, a species of caterpillar that feeds on cedars, arborvitae and other conifers. Bagworms do not make large masses of webbing. Instead, each caterpillar spins its sack of webbing and plant leaves, in which it hides while feeding.

The mass of webbing spun by fall webworms is known as a nest. Each nest can contain 300 to 900 webworms and are all hatched from the same mass of eggs laid by a female fall webworm on the underside of a leaf. The web is expanded as the young webworms grow and can get as large as 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, down the tree to form their cocoon.

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. Nests will naturally weather away during winter months.

Established trees can tolerate losing considerable 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.

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 the nest is on only if caterpillars can be seen actively feeding in the nest and pruning will not disfigure the tree.

If you should have other concerns about your trees, please call Nancy Olsen, Bladen County Cooperative Extension horticulture agent, 910-862-4591 or come by the office, 450 Smith Circle Drive in Elizabethtown.

Nancy Olsen
https://www.bladenjournal.com/wp-content/uploads/2018/08/web1_nrolsen-Copy.jpgNancy Olsen