Tent Caterpillars in High Trees: Safe and Effective Control

Managing Tent Caterpillars in Tall Trees

Eastern tent caterpillars (Malacosoma americanum) build silken tents in branch crotches of cherry, apple, and other trees. When nests are 40 feet up, physical removal is impractical. Here are safe, effective strategies.

Understanding the Pest

• One generation per year; eggs hatch in early spring.
• Caterpillars feed on leaves, returning to the tent for shelter.
• Trees can tolerate moderate defoliation; severe repeated defoliation weakens them.

Control Options

1. Biological Control: Bacillus thuringiensis (Bt)

Bt (e.g., Dipel, Thuricide) is a bacterial insecticide specific to caterpillars. It must be ingested, so spray foliage around and inside the tent. Apply when caterpillars are small (early instars). Reapply after rain. Safe for beneficial insects, birds, and pets.

2. Mechanical Disruption

• Use a long pole to tear open tents on a cool morning or evening when caterpillars are inside. This exposes them to birds and predators.
• If you can reach lower tents, prune and destroy them.

3. Encourage Natural Enemies

• Parasitic wasps, birds, and predatory insects attack caterpillars.
• Avoid broad-spectrum insecticides that kill beneficials.

4. Chemical Control (Last Resort)

If infestation is severe and tree health is at risk, a licensed arborist can apply systemic insecticides (e.g., acephate) via trunk injection or soil drench. Homeowner sprays rarely reach 40-foot canopies effectively.

What NOT to Do

• Do not burn tents—this damages the tree and is a fire hazard.
• Do not ignore the problem if the tree is small or already stressed.

Will They Return Next Year?

Yes. Egg masses overwinter on twigs. Scouting in late winter and scraping off egg masses (shiny, dark bands encircling twigs) can reduce next year's population.

For a 40-foot birch, Bt applied with a hose-end sprayer or hiring a professional for systemic treatment are the most practical options.