Tent caterpillars are moth larvae from the genus Malacosoma belonging to the family Lasiocampidae. These social caterpillars live in communal nests constructed in trees and shrubs. About 26 species are described globally, with six found in North America. They are a natural part of forest ecosystems and are sometimes considered pests due to their defoliating activities.
Recognizing Tent Caterpillars
Identifying tent caterpillars often begins with spotting their silken tents. Eastern tent caterpillars build their tents in tree branch forks, typically in early spring. These nests are expanded as the caterpillars grow, providing shelter and protection. In contrast, forest tent caterpillars, despite their name, do not build large, communal tents; instead, they spin inconspicuous silken mats on tree trunks and branches where they gather to rest.
The caterpillars themselves exhibit distinct appearances depending on the species. Eastern tent caterpillars are black with a white stripe down their backs, brown and yellow lines along their sides, and oval blue spots, and are also covered in long, pale hairs. Forest tent caterpillars are blue and black, featuring a row of white, footprint-shaped or keyhole-shaped markings along their backs. Western tent caterpillars are generally pale blue-gray with a light stripe down the middle of their back, bluish spots, and yellowish-brown hairs. These caterpillars grow to about 1.5 to 2.5 inches in length when mature.
Life Stages and Unique Habits
Tent caterpillars undergo complete metamorphosis, progressing through egg, larva (caterpillar), pupa, and adult moth stages. Females lay egg masses, often encircling small twigs, in late spring or early summer. These masses are covered with a frothy, protective material called spumaline, which hardens for overwintering. Larvae develop inside the eggs within a few weeks but remain dormant until the following spring, hatching as host tree leaves emerge.
Soon after hatching, young caterpillars construct silken shelters. These tents provide thermal protection, especially on cold spring nights, and offer refuge from predators and adverse weather. Caterpillars are social, living and feeding in groups, continuously expanding their tents as they grow, venturing out to feed on leaves often before dawn, around midday, and after sunset, and returning to the tent between bouts. As they move, they lay silk trails and pheromones, guiding other colony members to food sources and new resting sites. The larval stage typically lasts five to eight weeks, during which they grow rapidly and consume significant foliage, with the last larval stage consuming about 80% of all food eaten.
Once fully grown, caterpillars leave their host tree to find protected locations for pupation. They spin silken cocoons, often in sheltered spots on the ground, under building eaves, or on tree trunks and fences. About two to three weeks later, adult moths emerge. These adult moths are generally short-lived, typically living for about five to ten days, and their primary purpose is to reproduce and lay eggs, completing the annual life cycle.
Effects on Plants and Environment
Tent caterpillars are known for their defoliation of trees and shrubs, primarily due to their voracious feeding habits during the larval stage. They feed on a wide range of deciduous trees, including fruit trees like cherry, apple, and plum, as well as oaks, aspens, poplars, birches, and maples. During outbreaks, which occur cyclically every several years, they can strip entire tree canopies of their leaves.
While such defoliation can appear severe, healthy, mature trees can typically withstand it without permanent damage. Most deciduous trees can regrow a new set of leaves within the same growing season, usually by mid-summer, after the caterpillars finish feeding. However, repeated defoliation over several consecutive years, or defoliation of trees already stressed by drought, disease, or other factors, can weaken them, reduce growth, and in some cases, lead to branch dieback or tree mortality.
Beyond their impact on trees, tent caterpillars also play a role in the broader ecosystem. They serve as a food source for various predators, including birds, wasps, and spiders. Birds, such as orioles, bluebirds, and robins, frequently feed on the larvae, especially younger ones. For humans, large populations of tent caterpillars can be a nuisance, as they may crawl on buildings and roads, and their droppings can be noticeable.