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How to identify it
- Webs enclose leaves at the ends of branches and fill with caterpillars, partly eaten leaves and droppings. They start small and can reach 2 to 3 feet, and old gray webs hang on through winter.[1][3][2]
- Caterpillars grow to about 1 inch. They are pale green or yellowish with a broad dark stripe down the back and yellowish side stripes, and long tufts of whitish to gray hairs grow from black or orange warts.[1][2][4]
- Heads are black or red. Black-headed caterpillars make flimsy webs and red-headed ones build larger, denser webs; UMass describes the two as color forms of one species.[2][5]
- The moths are satin white, plain or with dark spots, and have orange-tinged hind wings and abdomen; spotted moths are commoner in the South. Penn State gives a wingspan of about 32 mm, UC IPM about 1 1/2 inches.[1][4][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Eastern tent caterpillar | Builds its tent in branch crotches in spring and leaves it to feed, while fall webworm webs enclose the leaves at branch tips from midsummer on and the caterpillars feed inside.[6][2][1] |
| Western tent caterpillar | Tent caterpillars usually web inner foliage around branch crotches, while webworms colonize the outer tips of branches.[4] |
Where it lives
Native to North America and Mexico and common through most of the United States and southern Canada. It has also spread across much of Europe and Asia; UMass notes it reached Hungary in the 1940s, and it is now an invasive pest in China.[5][2][7]
Biology and life cycle
It overwinters as a pupa in a thin cocoon in leaf litter, bark cracks or soil. Moths emerge from late spring into early summer, and Penn State says some keep appearing through most of the summer.[1][2][4]
Females lay masses of several hundred eggs (200 to 500, says Wisconsin) covered with white hairs on the undersides of leaves. They hatch in about a week, and the caterpillars start a web right away.[1][2][4]
The caterpillars feed together inside the web, enlarging it as they grow, and mature in about six weeks; in the last stage they may leave and feed alone before pupating in or on the soil.[1][2]
Webs get noticed late. UMass says larvae feed 3 to 4 weeks before webs become obvious; small webs appear in mid-July in Massachusetts, and Iowa sees them from mid-August.[5][3]
There are one or two generations a year depending on location: usually one in Wisconsin, two in warm years and warmer areas, and one or two in California.[1][2][4]
Damage and signs
- Caterpillars eat the leaves inside the web down to the veins. On shade trees the webs usually affect scattered branches and mainly spoil the tree's looks.[1][4][2]
- They may occasionally defoliate a tree but rarely kill it; by late summer trees have already stored the energy they need. Repeated defoliation plus drought, recent planting or construction can weaken a tree.[1][2][3]
- Hosts include hickory, walnut, birch, cherry, crabapple, elm, maple, mulberry, sweetgum (liquidambar) and willow, and Iowa's favorite host is black walnut. On fruit and nut trees, heavy defoliation can sunburn the crop.[1][2][3][4]
Health risk
None of the extension sources here lists a health risk to people; they treat fall webworm as a pest of trees whose webs mainly hurt appearance.[1][2][3][5]
Control
Prevention
Iowa State says sprays after mid-September are of no benefit and only harm the predators and parasites that keep webworms in check; often, simply tolerating the webs is fine.[3][2]
Traps and physical control
Prune out webbed branch tips within reach while webs are small, if it won't spoil the plant's shape. Higher webs can be pulled out with a forked stick, a pole with a crosswise nail or a brush on a telescoping pole, then destroyed.[1][2][4]
Biological control
More than 50 kinds of parasites and 36 kinds of predators attack fall webworms in North America, and birds eat the caterpillars. These enemies build up when webworms are numerous and bring them back down within a few years.[5][1][2]
Pesticides
If you treat, spray only the webs and nearby foliage while they are small, with enough pressure to get through the silk. Bt and spinosad are selective choices; Bt needs a second spray 7 to 10 days later, and spinosad should not go on plants in bloom.[1][4][2]
An American moth abroad
UMass says the fall webworm is now a worldwide pest: in the United States at least 88 tree species are hosts, while in Europe at least 230 are affected.[5]
In China, where it is invasive, researchers estimate current suitable habitat at about 118 × 10^4 km² and expect climate change to enlarge it, and lab work there found the larvae adjust their digestion to cope with many different host plants.[7][8]
Where sources disagree
Number of hosts: Penn State says almost 90 species of deciduous trees, UMass at least 88 in the United States, UC IPM more than 100 woody broadleaves and Iowa State more than 200 trees and shrubs.[1][5][4][3]
How long larvae feed: Penn State says caterpillars mature in about six weeks, while UMass says they feed 3 to 4 weeks before webs become obvious, so most feeding is done by the time many people notice.[1][5]
Moth size: Penn State gives a wingspread of about 32 mm, UC IPM about 1 1/2 inches.[1][4]
Common questions
- Will fall webworms kill my tree?
- Rarely. They may strip some branches, but on healthy, established trees the damage is mostly cosmetic and control is not essential.[1][3][2]
- Is it fall webworm or eastern tent caterpillar?
- Check where and when: spring tents in branch crotches are tent caterpillars, while midsummer and fall webs wrapped over branch-tip leaves are fall webworms.[6][1][2]
- Should I burn the webs?
- No. Wisconsin and UMass warn that burning webs on the tree likely does more harm than the caterpillars and can be a fire hazard; Kentucky gives the same advice for tent caterpillar nests. Prune or pull the webs instead.[2][5][6]
Sources
- Penn State Extension, “Fall Webworm (updated June 24, 2026).” extension.psu.edu/fall-webworm (accessed 2026-11-11)
- University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture, “Fall Webworm, Hyphantria cunea.” hort.extension.wisc.edu/articles/fall-webworm/ (accessed 2026-11-11)
- Iowa State University Extension and Outreach, “Fall Webworm (Yard and Garden encyclopedia).” yardandgarden.extension.iastate.edu/encyclopedia/fall-webworm (accessed 2026-11-11)
- University of California Statewide IPM Program, “Pest Notes: Fall Webworm.” ipm.ucanr.edu/home-and-landscape/fall-webworm/ (accessed 2026-11-11)
- UMass Amherst Extension, Landscape, Nursery and Urban Forestry Program, “Hyphantria cunea (Insect & Mite Guide).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/hyphantria-cunea (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-423: Eastern Tent Caterpillar (revised January 2026).” entomology.mgcafe.uky.edu/ef423 (accessed 2026-11-11)
- Ecology and Evolution, via PubMed, “Wen, Fang, Chai and others (2024), Can ecological niche models be used to accurately predict the distribution of invasive insects? A case study of Hyphantria cunea in China.” pubmed.ncbi.nlm.nih.gov/38487749/ (accessed 2026-11-11)
- Insects, via PubMed, “Zhang, Li, Yuan and others (2023), Digestive characteristics of Hyphantria cunea larvae on different host plants.” pubmed.ncbi.nlm.nih.gov/37233091/ (accessed 2026-11-11)
- iNaturalist, “Hyphantria cunea taxon page (order and family).” www.inaturalist.org/taxa/127133 (accessed 2026-10-06)