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Tent Caterpillar (Forest)


  • Eggs: In mid-summer, the female lays grey-coloured eggs in honeycomb-like bands of 150-200 eggs around small twigs of host trees. She then secretes a shiny dark-grey foam-like material called spumaline over the egg mass to protect it. After laying her eggs, she dies. Egg bands overwinter and hatch the following spring.
  • Larvae: Larvae hatch in mid-May, about the same time as trees begin to leaf out. The larvae have blue sides, a black back with a narrow white strip down the centre, and irregular orange markings. Larvae create web mat on large branches in locations where they eat. They feed for 6 weeks before migrating and swarming in mid to late June, to search for new food or cocooning sites. When fully mature in mid-July, tent caterpillars may be up to 50 mm long.
  • Pupae: Mature larvae pupate inside cocooning sites, found between leaves on a tree.
  • Adults: Adult moths emerge 10 days later from the cocoon tent. Adult moths are light buff-brown in colour and measure 25 to 37 mm across. Their forewings have two dark, oblique bands near the centre.

Identifying infestations:

  • Swarming tent caterpillars: Hundreds of tent caterpillars can be found in masses on the trunks and branches of infested trees.
  • Silken mats or “tents” on tree branches: Tent caterpillars create these silken mats or tents to live and feed.
  • Spurnaline egg nests on branches: This greyish, foamy band is easily seen in the fall and early spring, when trees have no leaves.
  • Defoliated trees: Under high population conditions, the tent caterpillar will devour almost all green foliage in their migration path.

IPM Toolkit:

  • Preventive tools:
    • Follow a regular watering, fertilizing, and pruning schedule to keep your trees as healthy as possible to resist attack.
    • Avoid planting trembling aspen trees (Populus tremuloides) which tent caterpillars prefer. However, tent caterpillars will also eat birch, saskatoon, green ash, apple, mayday, and most other deciduous trees and shrubs.
  • Physical tools:
    • Slit and remove egg bands by hand or prune branch where egg band is located.
    • Hand-pick and destroy caterpillars in areas where they cluster together in the evening or on cool days.
    • Place a sticky collar around the base of susceptible trees in June to trap migrating caterpillars.
  • Biological tools: Not applicable.
  • Least toxic chemical tools:
    • Apply Bacillus thuringensis var. kurstaki ( also known as Organic Insect Killer, Bt.k.) according to label directions to treat infestations