I see a lot of the Eastern Tent Caterpillars tents while hiking the Ouachita National Forest here in Arkansas during the spring. This year they don't seem to be as many.
The newly hatched caterpillars initiate the construction of a silk tent soon after emerging. They typically aggregate at the tent site throughout their larval stage, 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. The exception to this feeding pattern occurs in the last instar, when the caterpillars feed only at night. The insect has six larval instars. At the last stage, the caterpillars disperse and each constructs a cocoon in a protected place. The adult moths, or imagoes, emerge about two weeks later. They are strictly nocturnal and start flying after nightfall, coming to rest within a few hours of dawn. Mating and oviposition typically occur on the day the moths emerge from their cocoons; the females die soon thereafter. (Source: Wikipedia)
The Eastern Tent Caterpillar is of some importance as a pest because it defoliates ornamental trees. Damaged trees, however, typically recover and refoliate within several weeks.
Tent Caterpillars After Hatching - Ouachita National Forest - Arkansas