On my commute into the office this morning, I couldn’t help but notice how the fog and sunshine made the webby nests in all the trees glisten. Those webs, which cause homeowners much grief, are caused by the fall webworm. These builders of web houses are often confused with bagworms or the eastern tent caterpillar. But each of these creatures makes a different and very distinct home for their caterpillars. Let’s focus on the fall webworm.
Fall webworms can be up to one inch long. They come in two color forms. Those with black heads are yellowish white while those with red heads are brown. They are covered with long, soft gray hairs. Fall webworms will feed on more than 100 types of trees but they prefer trees like pecans, black walnut, mulberry, elm, sweetgum, willow, apple, ash and oak. They are most often seen in pecan trees.
The caterpillars form fine silken webs on the ends of the branches around the leaves they feed on. They will enlarge the webs if they need more leaves. They feed on the leaves for a couple of weeks before they leave the trees to become pupae. These pupae eventually turn into a white moth. This moth can fly away to lay eggs on trees to start another generation of webworms. There can be up to four generations of fall webworms in a year. The webworms survive the winter as pupae in cocoons in protected places.
Although these caterpillars do eat the leaves, healthy trees are able to withstand a great deal of insect damage to their leaves without lasting injury. One of the easiest things to do may be to do nothing. Treatment requires direct contact of an insecticide with the caterpillars inside the web, which would usually mean a ladder and a high pressure sprayer.