Overview
The Forest Tent Caterpillar Moth (Malacosoma disstria) is a defoliating insect known for periodic population outbreaks that can strip trees of their leaves. Despite its name, this species does not build tents like other tent caterpillars but instead forms loose silk mats on tree trunks and branches.
These caterpillars primarily feed on hardwood trees such as aspen, oak, and maple. During outbreak years, they can defoliate large areas of forest, affecting both natural ecosystems and residential landscapes.
The forest tent caterpillar moth (Malacosoma disstria) is one of the most widespread and well-known defoliators of deciduous forests across North America. Despite its name, this species is unique among tent caterpillars because it does not actually build a tent. Instead, the larvae spin flat, silken mats on the trunks and large branches of host trees—such as aspen, sugar maple, and oak—where they congregate between feeding bouts. The adult moths are relatively stout, buff-colored insects with two dark, oblique bands across their forewings, and they are frequently seen swarming around porch lights during their brief mid-summer flight.
The larval stage is easily identified by a row of distinct, white, keyhole-shaped spots running down the center of its blue-and-black back. During “outbreak” years, which occur in roughly 10-year cycles, populations can reach such extreme densities that they completely strip the leaves from millions of acres of forest. While healthy trees can typically survive a single defoliation by producing a second flush of smaller leaves, repeated attacks over three or more years can lead to significant “dieback” or even tree mortality, particularly if the forest is already stressed by drought. In residential areas, the sheer number of caterpillars crawling on sidewalks and houses can be a major nuisance. Natural control usually comes from “the friendly fly” (Sarcophaga aldrichi), a native parasite that helps crash the caterpillar population after a few seasons of heavy activity.
Identification
- Caterpillars are blue-gray with keyhole-shaped markings
- Fine hairs covering the body
- Adult moths are light brown
Habitat
Found in forests, parks, and residential areas with host trees. They are especially common in northern regions.
Behavior and Damage
Larvae feed on leaves, often consuming large amounts in a short time. Severe infestations can lead to complete defoliation.
While healthy trees can recover, repeated defoliation can weaken them significantly.
Prevention and Control
Monitoring populations, removing egg masses, and using biological controls can help manage outbreaks.