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Ministry of Agriculture, Food and Rural Affairs

Tent Caterpillars

Eastern tent caterpillar egg masses Eastern tent caterpillar nest in tree
Click to enlarge.

Beginner

Scientific Name
Malacosoma americanum (Eastern tent caterpillar) and Malacosoma disstria (Forest tent caterpillar)

Identification

 

Eggs

Larvae

Adults

Tents

Damage

Eastern Tent

Golden brown masses encircling young twigs.

The full-grown larva is 40-50 mm in length, hairy and brownish black with blue spots along the body and a white stripe running the length of the back.

Reddish brown moths with two distinct pale stripes that run diagonally across each wing.

Build a single large tent that is occupied through the whole larval stage.

One colony can strip the leaves of whole branches. Fruitlets on these branches fail to develop.

Forest Tent

100 to 350 eggs are laid in cylindrical masses around small twigs.

The full-grown larva is 40-50 mm in length, hairy and brownish black with a row of elongated spots along its back.

Reddish brown moths with two distinct brown stripes that run diagonally across each wing.

Do not build tents, but aggregate on silken mats that they spin on the leaves or bark of trees.

Often Confused With

  • Fall webworm infestations- Fall webworm is active in the fall (not spring or mid summer).  Fall webworm has webs in the outer regions of the branches, not in the central crotches of the tree (like tent caterpillars).

Period of Activity
Eggs hatch in early spring from overwintering egg masses; adult moths emerge in late June with egg laying occurring in July. These eggs hatch the following winter. There is only one generation per year.

Scouting Notes
Take note of tent caterpillar activity during regular orchard inspections from bloom through petal fall while monitoring for other pests. Tent caterpillar populations are generally localized, and do not reach levels that result in economic damage. Outbreaks tend to occur in forests at fairly regular intervals every decade or so. Often tent caterpillars move into orchards from adjacent woodlots.

Thresholds
None established.

Advanced

Scientific Name
Malacosoma americanum (Eastern tent caterpillar) and Malacosoma disstria (Forest tent caterpillar)

Identification
Eastern tent caterpillar
Eggs: Eggs are golden brown masses encircling young twigs.
Larvae: The full-grown larva is 40-50 mm in length, hairy and brownish black with blue spots along the body and a white stripe running the length of the back.
Adults: Reddish brown moths with two distinct pale stripes that run diagonally across each wing. 
Damage: Eastern tent caterpillars build a single large tent that is occupied through the whole larval stage. One colony can strip the leaves of whole branches. Fruitlets on these branches fail to develop.

Forest tent caterpillar
Eggs:  100 to 350 eggs are laid in cylindrical masses around small twigs.
Larvae: The full-grown larva is 40-50 mm in length, hairy and brownish black with a row of elongated spots along its back. 
Adults:  Reddish brown moths with two distinct brown stripes that run diagonally across each wing.
Damage: Forest tent caterpillars do not build tents, but aggregate on silken mats that they spin on the leaves or bark of trees. One colony can strip the leaves of whole branches. Fruitlets on these branches fail to develop.

Often Confused With

  • Fall webworm infestations- Fall webworm is active in the fall (not spring or mid summer).  Fall webworm has webs in the outer regions of the branches, not in the central crotches of the tree (like tent caterpillars).

Biology
Tent caterpillars overwinter as egg masses encircling young twigs, which are often detected during winter pruning. Each egg mass has 200-300 eggs. Eggs hatch in early spring and young eastern tent caterpillar larvae spin a characteristic tent in a limb crotch – where they reside as a colony – only leaving to feed on newly developing leaves in mornings and evenings. Forest tent caterpillars aggregate on silken mats they spin on the leaves or bark of trees. Adult moths emerge in late June with overwintering egg laying occurring in July. 

Period of Activity
Larvae are active from bloom through petal fall. There is only one generation per year.

Scouting Notes
Take note of tent caterpillar activity during regular orchard inspections while monitoring for other pests from bloom through petal fall. Tent caterpillars are generally localized and do not reach levels that result in economic damage. Tent caterpillar outbreaks tend to occur in forests at fairly regular intervals every decade or so. Often they move into orchards from adjacent woodlots.

Thresholds
None established.

Management Notes

  • Tent caterpillars do not require insecticide treatment.
  • Prune out infested branches, larvae and egg masses on affected trees.