Tent caterpillars are the larval stage of moths belonging to the genus Malacosoma, which is part of the family Lasiocampidae. These insects are instantly recognizable by the large, distinct silken structures they weave in the branches of trees in the spring. The communal silk tent serves as a shelter for the hundreds of larvae that hatch from a single egg mass, offering protection from predators and temperature fluctuations. This gregarious behavior and the conspicuous tents are often the first signs that these foliage-consuming larvae are active.
Primary Host Plants and Preferred Diet
The diet of tent caterpillars is strongly tied to the species, but most prefer trees and shrubs in the Rosaceae family. Eastern tent caterpillars (Malacosoma americanum) preferentially feed on the leaves of wild cherry, apple, crabapple, and plum trees. Western tent caterpillars (Malacosoma californicum) share these preferences but have a broader diet that also includes peach, pear, willow, and poplar. While they have a preferred menu, these insects can become opportunistic feeders, especially during large outbreaks. If the primary host tree is completely defoliated, the caterpillars will wander to consume foliage from less-favored plants. This expansion of diet ensures their survival. The forest tent caterpillar (Malacosoma disstria), a relative that does not build the classic silken tent, consumes a wider variety of hardwood species, primarily oak, maple, and aspen.
Feeding Stages and Patterns
Tent caterpillars consume foliage only during their larval stage, which lasts for about four to seven weeks in the early spring and summer. The newly hatched larvae begin feeding just as the host tree’s buds break and leaves emerge, ensuring they have a supply of tender, fresh growth. They are communal feeders, leaving the silk tent together multiple times a day to forage on nearby leaves. The caterpillars navigate their host plant by laying down silk trails and pheromone markers. When a caterpillar discovers a high-quality food source, it reinforces the silk trail with a recruitment pheromone to guide its tent-mates directly to the new leaves. This social foraging behavior allows the large colony to efficiently strip the foliage from a section of the tree. Defoliation can appear suddenly because the caterpillars do 80 to 90 percent of their total eating in the final few days of the larval stage before they pupate.
Impact of Defoliation on Trees
The feeding habits of tent caterpillars can result in the complete defoliation of a tree, which can look severe to a homeowner. Because the feeding period is short and occurs early in the growing season, most healthy, mature hardwood trees can withstand the damage. These trees typically recover by producing a second flush of leaves by mid-summer, allowing them to resume photosynthesis. The tree’s overall growth may be temporarily reduced, but the long-term health is generally unaffected. For trees that are already under stress from drought, disease, or old age, the impact of defoliation is much greater. Repeated defoliation over consecutive years can exhaust a tree’s energy reserves, potentially leading to branch dieback or death. The weakened state of a severely defoliated tree also makes it more susceptible to secondary issues, such as attack by wood-boring insects or diseases.