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..
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.
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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.
Kill caterpillars, spare everything else
Bacillus thuringiensis (Bt) only affects caterpillars — bees, birds, pets, and beneficials are totally safe. Kills feeding worms in 1-3 days. Read our full pick.
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.