Fall Webworm
Hyphantria cunea
📖 Description
The fall webworm is a common pest of deciduous trees recognized by the conspicuous silk web nests it builds at branch tips. Unlike tent caterpillars that appear in spring and build nests in branch crotches, fall webworms appear in late summer and fall and enclose the foliage at branch tips. While the nests are unsightly, they rarely cause serious harm to healthy, mature trees since most feeding occurs late in the season after trees have stored energy. However, young trees and trees under stress can be significantly weakened by repeated defoliation. The caterpillars remain inside the web during the day, expanding it as they consume more foliage.
⚠️ Symptoms to watch for
- Large silk web nests enclosing branch tips and foliage,Skeletonized and consumed leaves within the web,Caterpillars visible inside the webbing during the day,Web nests expanding as caterpillars grow and consume more foliage,Defoliation of branch tips, most noticeable in late summer and fall,Frass and leaf debris accumulating within the web
🩹 Treatment
- Prune out and destroy web nests when small (organic),Open nests with a stick to allow natural predators access (organic),Apply Bt (Bacillus thuringiensis) spray directly to the web (organic),Release Trichogramma wasps for egg parasitism (organic),Apply spinosad spray to foliage near the nest (organic),Use carbaryl (Sevin) or permethrin spray (chemical)
🌿 Organic treatments
- Prune out and destroy web nests when small,Open nests with a stick to allow natural predators access,Apply Bt (Bacillus thuringiensis) spray directly to the web,Release Trichogramma wasps for egg parasitism,Apply spinosad spray to foliage near the nest
🧪 Chemical treatments
- Use carbaryl (Sevin) or permethrin spray
🛡️ Prevention
- Inspect trees regularly in late summer for early web formation,Prune and destroy small nests before they expand,Encourage natural predators like birds, wasps, and predatory bugs,Remove and destroy leaf litter and debris in fall to reduce overwintering pupae,Band tree trunks with sticky bands to trap caterpillars,Maintain tree vigor with proper watering and fertilization
🪴 Affected plants
- Deciduous Trees,Fruit Trees,Ornamental Trees
🦋 Natural predators
- Birds,Parasitic Wasps,Predatory Bugs
🌱 Host plants
- Prunus spp.,Betula spp.,Acer spp.
🔄 Lifecycle
- Adults emerge in mid-summer from overwintering pupae in soil and leaf litter.
- Females lay 400-500 eggs in clusters on leaf undersides.
- Eggs hatch in 1-2 weeks.
- Larvae feed gregariously inside expanding silk webs for 4-8 weeks.
- Mature larvae leave the web, wander to find pupation sites, and spin cocoons in soil, leaf litter, or bark crevices.
- Pupae overwinter.
- One to two generations per year depending on climate, with the second generation being larger and more damaging.
📅 Season
- Late Summer to Fall
🔎 Appearance
- Larvae are very hairy caterpillars that vary from pale yellow to dark gray with rows of black or orange tubercles bearing long hairs.
- They build distinctive silk web nests at branch tips.
- Adults are white moths, sometimes with dark spots on the wings, with a wingspan of 25-35 mm.
💥 Damage level
- Moderate
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- North America
- Europe
- Asia
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