Have you seen webs spreading throughout your trees? They can be unsightly and leave brown patches where the webs are. Those are webworms. They are very common so let’s talk about these little guys that are spreading from tree to tree.
We have two types of caterpillars that make webs in trees in North Georgia. Eastern tent caterpillars will make webs in the spring. Fall webworms will make webs in the late summer or fall, hence their very original name. Webworms will have one to four generations each year. There are many different tree species that they will use to make their nest. They generally prefer to make their nests on deciduous trees over evergreens.
Webworms grow into a moth that has a one and a half inch wingspan. The wings are white and sometimes have black spots on them. The female moths will lay egg masses of up to 600 eggs. The egg masses are covered in hairs, which protects them from predators. When the caterpillars emerge from the eggs, they begin constructing nests on the ends of tree branches. The webworms will begin eating the new growth at the end of the branch. The webs that they construct protect them from predators and some insecticides. As the weather gets cooler, the caterpillars will burrow into the ground where they will pupate, the cocoon stage, and emerge as moths when the weather warms up again.
Webworms can heavily infest some trees. If a tree is heavily infested the webworms can completely defoliate the tree. Complete defoliation is not a common occurrence, but it is a possibility. Completely defoliating a tree leaves the tree bare and less attractive. However, deciduous trees are able to handle losing their leaves, because they will grow new ones back the next year.
In most situations, it isn’t necessary to remove the webworms from trees. The damage that they do is largely aesthetic. If there are some webs on lower branches that are easy to prune then physical removal of the branches is an option. If the branches are out of reach, it is possible to use a long pole or rake to knock the webs out of the tree. A pressure washer is also an option to remove webs from hard to reach places. Opening up webworm nests will expose them to the elements and enable predators such as birds, assassin bugs, and parasitic wasps to get inside and control the webworms too.
It is possible to use insecticides to control webworms, but I usually don’t recommend them because webworms rarely cause significant damage to the tree. If you decide to apply an insecticide one containing Bacillus thuringiensis (Bt) or spinosad will kill the webworms and not beneficial insects that are also nearby. Broad-spectrum insecticides like pyrethroids, which are any insecticide with an active ingredient ending with –thrin, will kill any insects it meets. You will have to open the nest first so that you get the insecticide inside the web. As always, read the label before applying a pesticide so that you know how to properly handle and apply the pesticide.
If you have questions about webworms contact your county Extension Office or email me at Jacob.Williams@uga.edu.