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Forest Tent Caterpillar

Malacosoma disstria

Author: Esther McGinnis


  • Forest tent caterpillar feed on the leaves of apple, crabapple and other fruit trees.
  • Caterpillars hatch in early to mid-May and will continue feeding for five to six weeks.
  • The larvae then spin cocoons and the adult moths appear in mid-July.
  • Feeding damage is conspicuous because caterpillars will consume entire leaves.
  • Despite their name, caterpillars do not spin silken tents.
  • These caterpillars are blue and black and have white keyhole spots down their backs.


Forest Tent Caterpillar

Figure 1. Caterpillars have prominent white keyhole markings. (James B. Hanson, U.S. Department of Agriculture Forest Service,

Management and other important facts


  • Mature trees can handle tent caterpillar defoliation better than younger trees.
  • If the tree is in flower, apply Bacillus thuringiensis (Bt) to the foliage. Bt is a biorational pesticide that will poison the caterpillars feeding on the treated leaves without hurting the bees or other pollinators.
  • Other biorational pesticides include spinosad and insecticidal soap.
  • If larvae are larger, conventional pesticides that include carbaryl or malathion may be more effective. Do not apply carbaryl within 30 days of petal fall to avoid fruit abortion.

This website was supported by the U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service through grant 14-SCBGP-ND-0038.
Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.

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