Field Identification
A highly polyphagous caterpillar that spins loose silk nests at branch tips in late summer and fall—unlike eastern tent caterpillar, the web encloses foliage at the ends of branches and expands as larvae feed. Outbreaks can defoliate shade trees, nut trees, and fruit trees; healthy wood usually releafs, but repeated stripping weakens stock and looks alarming. Native to the Americas and now familiar from southern Canada through the United States, Mexico, Central America, and the Caribbean on suitable hosts—activity shifts earlier in warm zones (roughly 6–11) and stays tighter to summer in cooler zones (3–8).
Adult moths are white with dark forewing spots; larvae vary from tan to greenish with dark stripes and long hairs. Webs accumulate frass and dry leaves, making infestations obvious from a distance. Several generations can occur where frost arrives late—scout August through leaf drop.
How to Deal With It
Organic Control Methods
Bacillus thuringiensis kurstaki targets small larvae feeding outside dense silk; penetrate the web enough to wet foliage inside. Neem or spinosad can follow labeled rates for caterpillars on ornamentals and some fruit trees. Spot-treat individual webs rather than blanket-spraying entire orchards to protect late-season pollinators.
Parasitic wasps (Ichneumonidae, Braconidae) and tachinid flies attack larvae; birds rip webs open. Maintaining understory habitat supports these enemies in shelterbelts and urban trees where repeated non-selective sprays are uncommon.
Accept light defoliation on mature landscape trees when webs are few—trees tolerate one cosmetic episode. In nurseries, isolate heavily webbed liners. Avoid unnecessary nitrogen flushes late in the season that push succulent tissue when moth flights peak.
Prune out accessible webs into a bucket of soapy water—effective on yard trees and reachable orchard limbs. For high branches, use a pole pruner on small webs before larvae grow large. Power washing webs is messy and often unnecessary compared with pruning.
Map trees that hosted webs each fall; inspect those first next season. In high-value blocks, walk outer rows weekly during late summer. Teach crews to distinguish fall webworm from tent caterpillar webs for correct timing with Bt.
Let Nature Handle It
Natural Enemies
- Tachinid Flies (Tachinidae)
- Ichneumonid Wasps
- Braconid Wasps
- Insectivorous Birds
Threat Map