Fall makes for great gardening weather, and as more folks wander back out into their gardens they are starting to notice the tips of their trees’ branches may have clusters of webbing on them. This usually leads to mild panic, because we have been conditioned to be hypervigilant to animals eating our plants. Given the time of the year and the location of these webs, it is a good chance they are fall webworms and there may be nothing to worry about!

What are fall webworms?

Fall webworms are a caterpillar of the species Hyphantria cunea (Drury, 1773). The 2-3 cm-long tent moth comes in two color forms: an all-white form and one with black spots that makes it look like it is wearing an ermine coat. It is quite beautiful and there is a good chance you’ve seen them flying around lights you may have left on.

These caterpillars and moths are active throughout the growing season in North Carolina, not just the fall, and they can make two generations per year. The webs may be more obvious towards the end of the year as our summer droughts thin out canopies and trees are just starting to look tired. Unlike eastern tent caterpillars that build their webs in spring near the trunks of trees, fall webworms locate their webs on the ends of branches.

Why not worry about them

While I always appreciate the diligence of gardeners and farmers when it comes to observation, sometimes observations do not require action on our part.

The fall webworm is a native insect to North America and has been recorded feeding on more than four hundred species of tree (Schowalter and Ring, 2017). I always tell my students that “leaves are cheap” (in most cases), especially in the case of large, hardwood trees, which have adapted to having their leaves feed thousands of species of caterpillars. This feeding is of little concern to most of these trees, and the damage is usually cosmetic for the home or property owner.

If you are concerned or feel you must act, you can use a rake to make a hole in the webbing to open up the webbing for birds and parasitic wasps to get in. You can also prune out the branch tip and compost it or throw it in the brush pile. Usually, though, the populations are controlled naturally, as at least 50 species of fly and wasp parasitoids and 36 species of predators, parasites, and pathogens are known to feed on fall webworm caterpillars (Schowalter and Ring, 2017).

When to worry about “worms” eating your trees

Fall webworms are of little concern in most cases, but there can be times to be more vigilant. If these insects are eating a young plant and impacting most of its canopy, that is a time to act. You should also be concerned if they are returning to trees that you are using for producing a crop, like fruit or pecan trees. In the case of pecan trees, a couple of fall webworm nests is okay. You should be concerned when most of the canopy is impacted. This may also be signalling you have an unhealthy tree and an unhealthy ecosystem in your area, as the natural predators are not present to keep the populations in check. Finally, if you notice heavy infestations year after year, you may need to consider how your management practices are impacting local populations of natural predators through time. Many of the parasitoid insects are tiny and need diverse, pesticide-free habitats to shelter in.

It can be challenging to spray for fall webworms, as the webbing is a natural repellent for most direct sprays. Some producers have used systemic sprays, but this is not generally recommended for home production systems and should be administered by a licensed pest control professional. Contact your local N.C. Cooperative Extension office to discuss if this is something you need to do.

Enjoy the free fertilizer

Caterpillars, like fall webworms, perform many different ecosystem functions as they go through their lives. The act of chewing up and pooping out leaf material is a type of nutrient cycling, so if you ever get frustrated with the fall webworms, just think, that might be less fertilizer you need to put out on your trees! These caterpillars also feed baby birds (if the adults can get in) and support insect diversity by feeding the parasitic insects that feed on them. They are part of the natural, healthy cycle of things and you can rest your mind on that.

Amanda Bratcher is the Horticulture Agent for North Carolina Cooperative Extension in Lee County.