The Eastern Tent Caterpillar is a social species that forms communal nests in the branches of trees. It is sometimes confused with the gypsy moth, or the fall webworm and may be erroneously referred to as a bagworm. The moths lay eggs almost exclusively on trees particularly cherry (Prunus) and apple (Malus). The caterpillars are hairy with areas of blue, white, black and orange.
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. The embryo forms and develops rapidly and within three weeks fully formed caterpillars can be found within the eggs. But the small caterpillars lie dormant 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 remain at the tent site for the whole of their larval life, expanding the tent each day to accommodate their increasing size. Under field conditions, the caterpillars feed three times each day, just before dawn, at mid-afternoon, 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, 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 6 inches back from the tip of a thin twig on host plants – cherry, apple and rose. They are easily seen all through winter. When fully grown, the caterpillars disperse and construct cocoons in protected places. The adult moths emerge about two weeks later.
Tent caterpillars secrete silk wherever they go and frequently used pathways soon bear conspicuous silk trails. As the caterpillars move about the tree, they largely confine their movements to these trails. Curiously, it is not the silk that they follow but a pheromone trail secreted from the posterior tip of their abdomen. Caterpillars deposit exploratory trails by dragging the tip of their abdomen as they move over the tree in search of food. Caterpillars that find food and feed overmark the exploratory trails they follow back to the tent, creating recruitment trails. Recruitment trails are much more attractive to the caterpillars than exploratory trails and they serve to lead hungry caterpillars directly to the newest food finds. It is possible for a single successful forager to recruit the entire colony to its food find.