Tent caterpillars vs fall webworm vs bagworm

Three garden pests build visible silk structures in trees: eastern tent caterpillar, fall webworm, and bagworm. They are unrelated, attack different trees at different times of year, and require different management approaches. Most gardeners conflate them because the silk is the most visible sign..

—- title: "Tent caterpillars vs fall webworm vs bagworm" slug: how-to-identify-tent-caterpillars-vs-fall-webworm hub: problems category: "Identification guide" description: "Tell eastern tent caterpillar, fall webworm, and bagworm apart by web location, timing, and host plants. Three very different pests that often get confused because they all make visible silk structures." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-

Three garden pests build visible silk structures in trees: eastern tent caterpillar, fall webworm, and bagworm. They are unrelated, attack different trees at different times of year, and require different management approaches. Most gardeners conflate them because the silk is the most visible sign. The location of the silk on the tree and the season it appears separate all three at a glance.

Eastern tent caterpillar (Malacosoma americanum)

When and where silk appears

Per Penn State Extension, eastern tent caterpillar builds silken tents in branch forks (crotches) — not over leaves, not at branch tips. The tent is in the fork where two or more branches diverge from a main stem. Tents appear in early spring, typically coinciding with early leaf emergence (March–April in zones 5–6). The tent is a communal shelter — the caterpillars return to it to rest and feed from it as a base.

Caterpillar appearance

Larvae are 2–2.5 inches at maturity. Per NC State Extension, they are dark blue-black on top with a white dorsal stripe, blue and yellow or red-orange spots along the sides.

Host plants

Eastern tent caterpillar strongly prefers cherry (Prunus), apple, crabapple, and hawthorn. Per Penn State Extension, wild black cherry (Prunus serotina) is the most commonly infested tree in the northeastern United States. It is also found on oak, maple, and other hardwoods.

Damage

The caterpillars defoliate branches in the vicinity of the tent. Per Penn State Extension, established trees are rarely killed by one season of defoliation but repeated defoliation weakens trees. The damage is severe-looking but recovery is usually complete.

Management

Remove tents by hand (by inserting a stick and twisting) or with a stream of water. Per Penn State Extension, Bt (Bacillus thuringiensis (BT spray) var. kurstaki) applied to foliage when caterpillars are small (first and second instar, early spring) is effective. Large tents with mature caterpillars are harder to treat.

Fall webworm (Hyphantria cunea)

When and where silk appears

Per Penn State Extension, fall webworm encloses leaf masses at branch tips in a loose, messy silk tent in late summer and fall (July–October). The web expands over time to include more leaves. The caterpillars feed inside the web — the web is not a resting shelter like the tent caterpillar's; it is the feeding arena itself.

Caterpillar appearance

Two color forms: pale yellow-green with black spots (northern form) and dark yellow-orange with orange spots (southern form). Per Penn State Extension, fall webworm is a variable species with geographic color variation.

Host plants

Extremely polyphagous — attacks more than 100 tree and shrub species. Per Penn State Extension, walnut, pecan, persimmon, and sweetgum are among the more commonly infested, but fall webworm will use any available hardwood.

Damage

Defoliation of branch tips late in the season, when trees are approaching dormancy. Per Penn State Extension, the damage looks dramatic but is rarely harmful because trees lose leaves naturally in fall anyway. The economic and ecological impact is minimal. Treatment is rarely necessary for healthy, established trees.

Management

Prune out and dispose of webs when small, in July. Per Penn State Extension, large webs on tall trees do not warrant treatment in most cases. Bt is effective if applied when caterpillars are small and foliage is accessible.

Bagworm (Thyridopteryx ephemeraeformis)

What bagworm looks like

Bagworm does not build a tent — it builds a spindle-shaped bag made from silk and bits of the host plant's foliage, which the larva carries like a shell and hangs from branches. Per Penn State Extension, the bag is most visible after host trees or shrubs drop their leaves in fall — at that point, hundreds of bags hanging in a landscape arborvitae, juniper, or spruce are a distinctive sign.

During the growing season, bags blend in because they are covered with leaf fragments from the host plant. A motionless bag on an arborvitae, 1–2 inches long, cylindrical, camouflaged with leaf bits = bagworm.

Host plants

Per Clemson HGIC, bagworm's preferred hosts are arborvitae, juniper, spruce, and other conifers. It also attacks deciduous trees (maple, sycamore) but is most damaging and most common on conifers. On conifers, the feeding kills foliage permanently — conifers do not resprout from bare wood.

Damage

On conifers, each feeding larva kills the foliage consumed. Per Penn State Extension, heavy infestations can defoliate and kill branches or the entire plant within a few seasons. Unlike tent caterpillar and fall webworm on deciduous trees, bagworm damage on conifers does not recover.

Management timing

Per Penn State Extension, management options:

• Hand-pick bags in fall and winter before the eggs hatch the following spring. Egg-filled bags hanging in trees represent next year's population.
• Bt or spinosad applied when caterpillars are small (1/4–1/2 inch) in late May–early June is the most effective spray treatment.
• Late-season sprays (August onward) are much less effective because larvae are large and have already caused the season's damage.

Three-way comparison

Recommended gear: Best BT Spray: Bacillus thuringiensis for Caterpillar Control — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.

Frequently asked questions

My arborvitae has brown dead patches every summer but I see no webs. Is this tent caterpillar? Probably not. Per Penn State Extension, bagworm damage on arborvitae begins as scattered brown patches on individual shoots during the growing season — not a tent or web. If you look carefully, you should see 1–2 inch bags camouflaged with arborvitae foliage. Bagworm is the most common cause of progressive, irregular browning on arborvitae that does not spread from plant to plant (unlike diseases).

Should I burn tent caterpillar tents? No. Per Penn State Extension, burning is ineffective and dangerous. The fire damages the branch more than the pest. Remove the tent manually with a stick or prune the infested branch during early morning when caterpillars are in the tent.

Can bagworm spread from one arborvitae to the next? Yes. Per Penn State Extension, bagworm populations spread by wind-blown larvae and by adult female moths laying eggs in bags that remain on the plant. An untreated infestation expands each season. Inspect adjacent conifers annually.

What does a natural predator of these caterpillars look like? Per Penn State Extension, numerous parasitic wasps attack tent caterpillar and fall webworm egg masses. Stinkbugs and predatory beetles consume young caterpillars. Chickadees and cuckoos are well-documented predators of tent caterpillars. Black-billed and yellow-billed cuckoos eat tent caterpillars preferentially — a marked uptick in cuckoo calling in spring often correlates with heavy tent caterpillar years in the Northeast.

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Sources:

1. Penn State Extension — Eastern tent caterpillar
2. Penn State Extension — Fall webworm
3. Penn State Extension — Bagworm
4. Clemson HGIC — Bagworm
5. NC State Extension — Tent caterpillar