Tent caterpillars are moderately sized caterpillars, or moth larvae, belonging to the genus Malacosoma in the family Lasiocampidae. Twenty-six species have been described, six of which occur in North America and the rest in Eurasia. Some species are considered to have subspecies as well. They are often considered pests for their habit of defoliating trees. They are among the most social of all caterpillars and exhibit many noteworthy behaviors.

Tent caterpillars are readily recognized because they are social, colorful, diurnal and build conspicuous silk tents in the branches of host trees. Some species, such as the eastern tent caterpillar, Malacosoma americanum, and caterpillars of the small eggar moth, Eriogaster lanestris, build a single large tent which is typically occupied through the whole of the larval stage, while others build a series of small tents that are sequentially abandoned. Whereas tent caterpillars make their tents in the nodes and branches of a tree's limbs, fall webworms enclose leaves and small branches at the ends of the limbs.