A tent caterpillar is the larval stage of a moth belonging to the genus Malacosoma, native to North America. These insects are highly social and build conspicuous, dense, silken structures in the branches of host trees. The sight of these communal silk nests, which appear in the spring, is often the first sign of their presence. They are active for a short period each year, known for their collective feeding habits.
Identifying the Species and Their Tents
Identifying the specific type of tent caterpillar often involves observing the caterpillar’s markings and the placement of its tent. The Eastern Tent Caterpillar (Malacosoma americanum) is recognized by a solid white or yellowish stripe running down the center of its black, hairy body, flanked by blue spots. Its tent is typically built in the fork or crotch of a branch, serving as a central home base for the colony.
The Western Tent Caterpillar (Malacosoma californicum) has a pale blue body with orange spots and two black stripes along its back, and it also constructs a visible silk tent in branch crotches. In contrast, the Forest Tent Caterpillar (Malacosoma disstria) does not build a true, enclosed tent. Instead, it spins a silken mat or pad on the trunk or branches for molting and resting, identifiable by a row of white or yellowish, keyhole-shaped spots running down its dark blue back.
The silk tent provides a stable microclimate for the colony, offering warmth and protection from predators and harsh weather. Caterpillars emerge to feed, returning to the nest in groups by following chemical pheromone trails they deposit. Fall Webworms, which also build webs, appear later in the summer and enclose the leaves at the ends of branches, distinguishing them from tent caterpillars.
The Annual Life Cycle
The tent caterpillar life cycle begins with the egg mass laid in late spring or early summer. Adult female moths deposit 150 to 300 eggs in a dark, spindle-shaped mass that encircles a small twig of the host tree. The embryo develops into a fully formed caterpillar within the egg during the late summer, where it remains dormant and protected throughout the winter months.
Hatching occurs the following spring, timed to when the host tree’s buds break and new foliage emerges. The newly hatched larvae immediately begin to construct their characteristic silk tent and enter the feeding stage, which lasts for approximately five to seven weeks. Once the caterpillars reach their full length of up to two inches, they disperse from the communal tent in search of a protected spot.
Each individual then spins a tough, yellowish-white silk cocoon to enter the pupal stage, often attached to bark, fences, or debris. After about two weeks inside the cocoon, the reddish-brown adult moth emerges in early summer. The nocturnal adult moths live only for a few days, mating and laying the next generation of eggs before dying, completing the annual cycle.
Potential Damage and Removal
The primary concern with tent caterpillars is the defoliation they cause during their larval feeding stage in the spring. They prefer deciduous trees, such as cherry, apple, crabapple, plum, and various oaks. Although an infestation can strip a tree of its leaves entirely, the damage is primarily cosmetic because the feeding occurs early in the season.
Healthy trees are usually able to produce a second set of leaves by mid-summer, allowing them to recover without lasting harm. However, repeated, severe defoliation over multiple consecutive years can weaken the tree. This reduces its growth potential and makes it more susceptible to stressors like drought or disease.
For homeowners concerned about an infestation, several non-chemical removal methods are effective. Control can begin in late fall or winter by inspecting twigs for the dark, varnished-looking egg masses and pruning them out before they hatch. Once the larvae emerge and the tents are visible in early spring, the entire colony can be removed by clipping off the branch containing the silk nest.
The most effective time to remove the tents is on cool or rainy days, as the caterpillars are usually gathered inside the shelter. If the tent is on a large branch where pruning is impractical, a stick can be used to twist the silken structure and its occupants out of the tree. The removed tents, egg masses, and caterpillars should be destroyed by placing them in a sealed bag or dropping them into a bucket of soapy water. Targeting the insects early in the season when the tents are small is the most straightforward method of control.