Eastern Tent Caterpillar on Crabapple: Identification & Control

Question: Crabapple infested with ½–1″ black worms in funnel-shaped silk web nests. What to do?

Answer: Eastern Tent Caterpillar (Malacosoma americanum)

Life Cycle

• Overwinter: egg masses (150–400 eggs) encircling pencil-thick branches, shiny black varnish coating
• Hatch: early March (bud break)
• Social: build silk tent in branch crotches; multiple masses may merge
• Feed: early morning, evening, night (not cold)
• Larvae: hairy, black, white back stripe, brown/yellow side lines, blue side spots
• Mature (4–6 wks): 2–2.5″, wander to spin cocoons
• Adult moth: reddish-brown, two pale diagonal forewing stripes
• One generation/year

Natural Controls

Parasitic wasps (braconid, ichneumonid, chalcid), predators, diseases → population cycles.

Control Options

1. Winter: Remove/destroy egg masses (prune or scrape)
2. Early spring: Remove small tents by hand
3. Larger tents: Prune out or wind on stick
4. DO NOT BURN: Damages tree
5. Bt (Bacillus thuringiensis var. kurstaki): On young larvae
6. Other insecticides: Carbaryl, methoxychlor, malathion (tents protect larvae)

Damage Perspective

Early spring defoliation = low energy cost to tree. Typically refoliates June. Rarely kills trees.

Hosts

Fruit trees, ash, maple, oak, rose family (crabapple, plum, pyracantha).

Resource

UMass Fact Sheet