Eastern Tent Caterpillar - Social Species

Social Species

In terms of complexity of interactions, the tent caterpillar stands near the pinnacle of caterpillar sociality. The adult moth lays her eggs in a single batch in late spring or early summer. The egg masses contain on average 200-300 eggs. Embryogenesis proceeds rapidly, and within three weeks, fully formed caterpillars can be found within the eggs. But the small caterpillars lie quiescent until the following spring, chewing their way through the shells of their eggs just as the buds of the host tree begin to expand.

The newly hatched caterpillars initiate the construction of a silk tent soon after emerging. They typically aggregate at the tent site for the whole of their larval lives, expanding the tent each day to accommodate their increasing size. Under field conditions, the caterpillars feed three times each day, just before dawn, at midafternoon, and in the evening after sunset. During each bout of feeding, the caterpillars emerge from the tent, add silk to the structure, move to distant feeding sites en masse, feed, and then return immediately to the tent where they rest until the next activity period. When there is a major population of eastern tent caterpillars, they can be controlled fairly well and easily with no pesticides. The egg masses, shiny reddish-brown, and looking like dried foam, are easy to spot, usually about six inches back from the tip of a thin twig on host plants: cherry, apple and rose. They are easily seen all through winter. The exception to this pattern of feeding occurs in the last instar, when the caterpillars feed only at night. They lay down pheromone trails to guide their movements between the tent and feeding sites. The insect has six larval instars. When fully grown, the caterpillars disperse and construct cocoons in protected places. The adult moths (imagos) emerge about two weeks later. They are strictly nocturnal and start flying after nightfall, then possibly stop some hours before dawn. Mating and oviposition typically occur on the same day the moths emerge from their cocoons; the females die soon thereafter.

Tent caterpillars, like many other species of social caterpillars, vigorously thrash the anterior part of their bodies when they detect predators and parasitoids. Such bouts of thrashing, which may be initiated by a single caterpillar, radiate rapidly though the colony and may result in group displays involving dozens of caterpillars. Such displays create a moving target for tachinid flies, wasps and other small parasitoids that lay their eggs on or in the body of the caterpillar. They also clearly deter stink bugs and other timid predators. Groups of caterpillars resting on the surface of the tent constitute aposematic displays. Few birds other than the cuckoo find the hairy caterpillars palatable. The leaves of the cherry tree are cyanogenic and the caterpillars regurgitate cyanide-laden juices when disturbed.