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Forest tent caterpillar, Malacosoma disstria, occurs throughout Canada and the United States and is a generalist defoliator that feeds on a variety of hardwood trees. In the north and west of the United States (and southern Canada), trembling aspen (Populus tremuloides) is preferred. In the southern United States, various gums (Nyssa spp. and Liquidambar styraciflua L.) and oaks (Quercus) are the common hosts. However, during outbreaks, larvae will feed on a wide variety of hardwood species. Winter is passed as eggs, which hatch in spring. Larvae begin feeding on buds and expanding leaves. Older larvae feed on mature leaves. Young larvae feed in groups, but older larvae are dispersed. Larvae lay silk trails, which they follow, but they do not form a silken tent. Rather, they make silk mats on which larvae rest. Mature larvae wander and pupate inside a yellowish-white cocoon fixed to the host tree or other objects. Adults emerge in midsummer (north) or spring (south) and lay their eggs in clusters that encircle twigs of the host tree. Eggs are cemented together and covered with dark colored material called spumaline. There is one generation per year. A number of very large outbreaks, covering thousands of square miles and lasting for several years, have occurred in North America. Tree mortality is generally low, but loss of growth can be considerable (>70%) due to effects of defoliation. In the southern United States, in bottomlands, gum trees may die from defoliation. In the northeastern United States, defoliation of sugar maple stands lowers maple syrup yields and quality.