Fall Webworm Nests
By Buggy Joe
August 14, 2025
Participants in the OGIA-OSU Diagnostic Walk-About held this past Monday at the Cincinnati Botanical Garden and zoo found a second-generation Fall Webworm (Hyphantria cunea, family Erebidae) nest. The webworms were the black-headed biotype, but more on that later.
Although fall webworm is a native species, the silk-nesting caterpillars have fallen from being a common sight in Ohio to virtual no-shows over much of the state for the past few years. For example, I posted a BYGL Alert in 2023 titled, “Fall Webworms are Conspicuous by Their Absence.” Last year’s BYGL Alert was titled, "Will Fall Webworm Make a Comeback in Ohio?”
Of course, finding a few fall webworm nests does not necessarily signal that fall webworm populations are on the rise. Still, this nest-maker has a long history of dramatic swings in population densities from year to year. That’s because this native insect has a cadre of enemies that can cause the fall of fall webworms.
A Fall Webworm Basics
Fall webworm caterpillar may feed on more than 600 species of trees and shrubs. Host trees are predominately hardwoods but fall webworm also may feed on several conifer species such as baldcypress (Taxodium distichum L.).
Black-Headed Fall Webworm on Baldcypress
The webworm caterpillars feed on the leaves enveloped by their silk nest unless they run out of leaf-food. Early instar caterpillars feed as leaf skeletonizers, and later instars consume all of the leaf tissue except for the petioles and coarse veins.
Early Instar Black-Headed Webworms Skeletonizing Redbud
Red-Headed Webworm on American Elm
As the caterpillars develop, they expand their nest by casting silk over an increasing number of leaves to accommodate their expanding appetites. However, the caterpillars may leave their nests in search of food if they defoliate their tree host before they complete their development.
Red-Headed Fall Webworms Feeding Outside of the Nest
Hairs on other caterpillars are sometimes used as defensive tools. However, the hairs on fall webworms are primarily used to help them remain suspended inside their silk nests. You can see this in the following picture. Note that the hairs fold back as the caterpillar appears to "swim" through the nest.
Red-Headed Webworm Moving Through the Silk
The common name "fall webworm" is based on when we typically see the largest nests. Female moths tend to lay their eggs on or near the nests from which they developed, with webworm nests becoming larger with each generation. I’ve often wondered if fall webworm silk includes an oviposition stimulant, as has been documented with mimosa webworm (Homadaula anisocentra). However, I’ve found no published research describing such an investigation.
We typically see two generations in Ohio: sometimes three. Thus, the nests reach their zenith in the fall (both astronomical and meteorological), which accounts for the common name.
I believe we are seeing second-generation nests in southwest Ohio. However, that can depend on the biotype.
Untangling Biotypes
Two forms of the caterpillars are recognized based on the color of the head capsules and body, as well as the color of small bumps from which the hairs arise, called “tubercles,” that run in longitudinal lines along the top of the caterpillar’s body. The two forms are variously referred to as “races,” “biotypes,” or “color-forms.”
The caterpillars referred to as the “red-headed biotype” have red to reddish-orange head capsules and tubercles that range from orangish-yellow to dark red. The caterpillars are most often tawny-colored.
Early Instar Red-Heade Webworm - Redbud
The “black-headed biotype” has black head capsules and black tubercles. The caterpillars are pale yellow to yellowish-green; however, they sometimes appear black with starkly white hairs.
Early Instar Black-Headed Webworms on Camperdown Elm
Black-Headed Fall Webworm Skeletonizing Persimmon
The two biotypes were once considered separate species with the black-headed biotype called H. textor and the redheads H. cunea. They are now considered the same species, H. cunea, with the biotypes representing variability within the species. Indeed, in 2016, I photographed a group of fall webworm caterpillars that showed features characteristic of both biotypes indicating they are capable of cross-breeding. Although these webworms are sometimes referred to as “hybrids,” the designation only applies to offspring of two different species.
Red-Headed Fall Webworm with Black-Headed Features
Ohio is home to both the red-headed and black-headed biotypes. Historically, northeastern Ohio was the dominion of red-headed fall webworms. The central and southwestern parts of the state were where we found black-headed webworms.
I never found red-headed webworms in Greater Cincinnati before 2016. However, groups of redheads began to appear in the western part of Hamilton County and gradually became the dominant biotype in southwest Ohio.
Red-Headed Fall Webworm Nest Black Walnut
Over the past few years, black-headed webworms have once again become the dominant biotype in southwest Ohio. In fact, all of the nests I found last season in southwest Ohio were black headed, and I have not found a red-headed webworm nest in my part of the state thus far this season.
Black-Headed Fall Webworm on Black Willow
The occurrence of two types of webworm caterpillars is significant because many of the differences between the biotypes that supported the “two species view” remain evident. Those differences include body coloration, the time of the season when overwintered eggs hatch, nesting behavior, and to some extent, host preferences.
There is a strong association between the biotype and the time of the year when we first notice fall webworm nests. Overwintered eggs of the red-headed biotype tend to hatch much later than the eggs of the black-headed biotype. The lag time may be as long as 4 weeks meaning the generational times between the two biotypes is not synchronous.
Red-headed fall webworms are much more damaging compared to black headed webworms. The redheads produce communal nests that my include caterpillars from a large number of egg masses. They can produce some truly spectacular multilayered nests enveloping whole branches or even entire small trees.
Red-Headed Fall Webworm Nest Black Walnut
Red-Headed Webworm Defoliated Crabapple
In 2021, Yellow Springs, OH, suffered from an outbreak of red-headed fall webworms. Trees were encased in webbing and suffered heavy to complete defoliation. Eastern black walnut (Juglans nigra) was by far the primary target.
Red-Headed Outbreak Black Walnut - 1
Red-Headed Outbreak Black Walnut - 2
Red-Headed Outbreak Black Walnut - 3
Red-Headed Outbreak Black Walnut - 4
Black-headed fall webworm nests appear to include caterpillars from only a few egg masses, if not just a single egg mass. Consequently, they tend to produce small, wispy nests that envelop only a dozen or so leaves. It’s common for several of these small nests to be found on the same branch. However, black-headed fall webworms seldom produce the heavy damage observed with red-headed webworms, even during “outbreak” years.
Black-Headed Webworm on Black Walnut
Black-Headed Fall Webworm on Sweetgum
Management
Nature Finds a Way: Fall webworm caterpillars must survive a bevy of predators, parasitoids, and pathogens (the 3-Ps). Research has revealed that over 50 different parasitoids and 36 species of predators help to keep fall webworms in check.
Cocoons in a Fall Webworm Nest
Two-Spotted Stink Bug Nymph A Webworm Nemesis
Ground Beetle Larva in a Fall Webworm Nest
These natural enemies play a significant role in fall webworm populations rising and falling dramatically from year to year. For example, the population “crash” in Yellow Springs was substantial, with no nests being evident in 2022.
Generalized Population Dynamics Chart
Insecticides: Applications of traditional insecticides such as pyrethroids (e.g., bifenthrin, permethrin, cyfluthrin, etc.) as well as other broad-spectrum insecticides such as acephate are effective. However, the applications can kill beneficial bio-allies that keep the webworms in check.
So-called biorational insecticides, which have a limited effect on non-targeted organisms, have less of an impact. These include products based on the active ingredients azadirachtin, chlorantraniliprol, spinosad, and tebufenozide. The naturally occurring bacterium, Bacillus thuringiensis Kurstaki (Btk), only kills caterpillars; however, it is most effective on early instars.
Three-Step Digital Destruction: Fall webworm caterpillars tend to congregate within their nests during the day. This handy behavioral trait makes the webworms, along with their unsightly nests, susceptible to digital removal. It is a highly satisfying approach and very effective. Thus far, no webworm populations have become resistant. The 3-Step Surefire Webworm Annihilation Technique (SWAT) is demonstrated with the following images.
Red-Headed Fall Webworm on Pecan Daytime
SWAT Step 2: Place Nest on Hard Surface
The following demo is rate TV MA V – Viewer Discretion Advised
SWAT Team Step 3: Maximum Compression
NOTE: Small webworm nests at the ends of branches can be pruned from trees and destroyed if the pruning doesn’t affect the overall desired tree form. Otherwise, it’s best to use SWAT.
Selected References
Hattori, I. and Ito, Y., 1973. Status of black-headed and red-headed types of Hyphantria cunea (Drury) (Lepidoptera: Arctiidae): II. External characters of the two types and their hybrids. Applied Entomology and zoology, 8(3), 172-182.
https://doi.org/10.1303/aez.8.172
Ito, Y. and Warren, L.O., 1973. Status of black-headed and red-headed types of Hyphantria cunea (Drury)(Lepidoptera: Arctiidae): I. Biology of two types and results of crossing experiment. Applied Entomology and Zoology, 8(3), 157-171.
https://doi.org/10.1303/aez.8.157
Ito, Y. and Hattori, I., 1975. Status of black-headed and red-headed types of Hyphantria cunea (DRURY)(Lepidoptera: Arctiidae): III. Distribution of various types and the discussion on the relationship among them. Applied Entomology and Zoology, 10(3), 189-202.
https://doi.org/10.1303/aez.10.189
Oliver, A. D. (1964a). A behavioral study of two races of the fall webworm, Hyphantria cunea,(Lepidoptera: Arctiidae) in Louisiana. Annals of the Entomological Society of America, 57(2), 192-194.
https://doi.org/10.1093/aesa/57.2.192
Oliver, A. D. (1964b). Studies on the biological control of the fall webworm, Hyphantria cunea, in Louisiana. Journal of Economic Entomology, 57(3), 314-318.
https://doi.org/10.1093/jee/57.3.314
Morris, R. F. (1963). Synonymy and Color Variation in the Fall Webworm, Hyphantria cunea Drury (Lepidoptera: Arctiidae) 1. The Canadian Entomologist, 95(11), 1217-1223.
https://doi.org/10.4039/Ent951217-11
Schowalter, T. D., & Ring, D. R. (2017). Biology and management of the fall webworm, Hyphantria cunea (Lepidoptera: Erebidae). Journal of Integrated Pest Management, 8(1), 7.
https://doi.org/10.1093/jipm/pmw019
Tadić, M.D. (1963). Natural enemies of fall webworm (Hyphantria cunea DR.) in north America. Entomophaga 8, 245–252.
https://doi.org/10.1007/BF02377530