Much Ado About Nothing

The sight of an extensive web formed at the end of tree branch resulting in leaf defoliation is a cause of quite the commotion. This commotion is absolutely justifiable at certain times of the year. In the case of fall webworm, the commotion is much ado about nothing. This installment of the Nine Minute Naturalist will give an in depth look at this unsightly pest.

The fall webworm is native to Virginia and most of the United States. It will feed on over 100 tree species but is seen most often at Wintergreen on hickories, oaks and ash. This species tends to become a focal point of the forest landscape in late July through August. The eggs laid May to July hatch and the caterpillar immediately begins constructing a web around the terminal end of a branch, making it especially conspicuous. The caterpillar is identified by it’s white to pale yellow color with two lines of black dots down the back. As the caterpillar grows, the webs enlarge encircling more of the branch. The leaves are stripped except the midrib and larger veins in the leaf.

After reading this description of unsightly defoliation happening all over our forested landscape, I am sure you are wondering why is this much ado about nothing? The primary reason this is not considered a devastating forest pest is the timing. By mid to late summer, the process of photosynthesis has mostly shut down. As the day lengths begin to get shorter and shorter, the feeding of the leaves for the production of chlorophyll begins to abate and the large amount of nutrients goes to the seeds, such as acorns, and buds that will be next year’s leaves. When a pest comes along in August and begins to eat leaves on a tree, it adds very little stress to the tree since the process of leaf drop has already begun. The second major reason to not fret over your trees being loaded with webs at the moment is that since this is a native species there are built in control mechanisms. Native pests tend to have native predators that have adapted to take advantage of the increase in the prey volume. There are a host of wasps and birds that like to feed on fall webworm. There are reportedly 50 species of parasitoids and 36 predators that call fall webworm their prey. That is a lot of control on a year to year basis.

The best option to control this pest yourself, if you don’t feel like waiting for nature to regulate the problem for you, is to cut the branch off below the web and burn the it. Chemical application is not very effective on web caterpillars since it doesn’t penetrate the web to get on the leaves they are eating.

The 2020 summer has been a unique one to say the least and that includes our vast amount of fall webworm amongst the landscape. While the population is booming, I am confident the built-in control mechanisms will do their job and your trees will come through this scourge unaffected. The fall webworm, while unsightly, is much ado about nothing.