This is particularly noticeable during outbreaks of the forest tent caterpillar. The tent of this species is among the largest built by any tent caterpillar. Outbreaks of western tent caterpillar can cause large scale defoliation of trees. Forest tent caterpillar populations increase periodically to outbreak densities. The eastern tent caterpillar is toxic to horses. It is a tent caterpillar found in Europe. Malacosoma californicum, the western tent caterpillar, is a moth of the family Lasiocampidae. The most notorious of the outbreak species is the forest tent caterpillar. The eastern tent caterpillar defoliates entire groves some springs. The mature Western Tent caterpillar pre-pupa is 4-5 centimeters long. Western tent caterpillar larvae are generalist herbivores, feeding on leaves. The eastern tent caterpillar infestation in the spring of 2001 was extraordinary. Leaf-eating insects, especially the forest tent caterpillar, Malacosoma disstria, occasionally defoliate trees. The eastern tent caterpillar regurgitates a droplet of digestive fluid to repel attacking ants.