Extension offices all over South Carolina are receiving numerous calls about “spider-looking” webs on the ends of tree branches.
Looking like an out-of-place Halloween decoration, these creepy-looking white, filmy structures are filled with caterpillars that consume the foliage of the host tree. Sometimes people call them “bagworms,” but that name applies to a different pesky caterpillar in a much smaller, pine-cone-shaped, foliage-encrusted bag.
What we find inside these large webby white “bags” on branch tips are many larval insects called fall webworms. The one-inch-long, light yellow to greenish “worms” have a black to reddish head. he body has two long black stripes and is covered in long, white hairs.
They are not true worms, but caterpillars of the moth Hyphantria cunea . These moths and their caterpillars are closely related to the Isabella moth, whose larva is called the woolly bear caterpillar.
Covered with its teddy-bear-like coat of long brown and black hairs, the familiar “woolly worm” or “fuzzy worm” is said to predict the severity of winter by the width of the brown vs. black bands. The wider the rusty brown section, the milder the coming winter will be, so they say. The more black there is, the more severe the winter.
Research has shown that this is somewhat true, but the width of the woolly worm’s stripes may relate more to the temperatures of the previous year than to the coming winter season.
Let us now leave the woolly worm myth and get back to the ugly nests of its cousin, the fall webworm. Native to the United States, the webworm can be found on 90 different species of deciduous trees. Most commonly, we hear complaints about them on pecan trees, but they also occur on hickory, persimmon, sourwood, walnut, birch, cherry, and crabapple in the Pee Dee.
The hungry caterpillars will eat the foliage, sometimes nearly defoliating the tree. But most of the time, they do not do significant damage and the tree makes a full recovery. When the caterpillars mature and leave the web, they will pupate and overwinter in tree bark or leaf litter at the base of the tree.
Since they usually don’t kill the tree, and since tall trees are so difficult for the homeowner to spray, we usually don’t recommend insecticide sprays for fall webworms.
An effective way to get rid of the webworms is to break up the unsightly web with a rake, broom or pole (if you can reach it) or a strong blast of water so that birds and other natural enemies can more easily get to them.
Webworms are the subject of an excellent blog entry at the Clemson Extension Home and Garden Information Center’s website https://hgic.clemson.edu/fall-webworm-management/.
You can also call HGIC 1-888-656-9988 for helpful control information, Monday through Friday from 8 a.m. to 4:30 p.m. (except university holidays). I hope you see more woolly worms than webworms this fall!
Trish DeHond is the home horticulture agent and Master Gardener coordinator for Clemson Extension in Darlington and Florence counties. She can be reached by email at firstname.lastname@example.org.