Tentworms

Integrated pest management photos and files

Common name

Tentworm (Malacosoma disstria)

Tent Caterpillar (Malacosoma disstria)
Forest Tent Caterpillar (Malacosoma californica)
Western Tent Caterpillar

Host plants

Deciduous trees and shrubs

Adults are stout, light to dark brown moths that are usually seen in midsummer (Figure 1). Larvae are hairy, dull-colored caterpillars with a variety of colored spots along their sides. Larvae feed on the host plant’s leaves in silken tents.

*Figure 1 — Tentworm female with egg mass.*

Biology

Tent caterpillars overwinter as eggs laid in masses on branches, twigs or buildings (Figure 2). There is only one generation per year.

*Figure 2 — Tentworm late stage larvae of mixed instars.*

Damage

Usually are only a problem if they occur on the same plant for multiple years
Can defoliate small trees if not controlled
This pest mostly weakens the tree/shrub, which causes additional pests and diseases to attack the tree
Look for egg masses in late summer to fall
Watch for worm damage in the spring and silken tents

Management

Physical

Direct physical manipulation of the pest or its environment, e.g. hoeing, tilling, using physical barriers or traps.

Remove and destroy overwintering egg masses when pruning

Biological

Many natural predators like birds, small mammals and tachinid flies

Cultural

Changing the way the crop is grown to make it less suitable for the pest or to enhance its ability to withstand pest attack.

Keep trees healthy

Chemical

Use dormant season oils for egg control
Caterpillars can be controlled when small if sprayed early in the spring after egg hatch
Plant-specific recommendations for pesticides to use in the management of tent caterpillars can be found on the PNW Insect Management Handbooks website

Pesticide warning
Always read and follow the instructions printed on the pesticide label. The pesticide recommendations in this University of Idaho webpage do not substitute for instructions on the label. Pesticide laws and labels change frequently and may have changed since this publication was written. Some pesticides may have been withdrawn or had certain uses prohibited. Use pesticides with care. Do not use a pesticide unless the specific plant, animal or other application site is specifically listed on the label. Store pesticides in their original containers and keep them out of the reach of children, pets and livestock.
Trade names — To simplify information, trade names have been used. No endorsement of named products is intended nor is criticism implied of similar products not mentioned.
Groundwater — To protect groundwater, when there is a choice of pesticides, the applicator should use the product least likely to leach.

Photo credit

Figure 1. USDA Forest Service, Bugwood.org (Jerald E. Dewey)
Figure 2. Colorado State University, Bugwood.org (Whitney Cranshaw)

Andy West, Extension educator, horticulture
2023