Social caterpillars, as shown in this video of the fall webworm, often engaged in synchronous defensive body-shaking in response to a sudden sound. In this case, the response is to a recorded sound, but aggregated caterpillars may also respond in unision to the sound of a buzzing predator wasp or a bird.
Synchronous foraging activity of 5th instar fall webworm larvae over a five-day period The caterpillars leave the nest at dusk en masse, then, after feeding overnight, return to the nest at daybreak. Nocturnal foraging is likely an adaption that allows caterpillars to avoid day-active predators. (Gray area = nightime)
During the first three instars, the caterpillars are patch restricted foragers, confining their foraging activity to a silken web spun over the leaves on which they feed. In the the 4th and subsequent stadia, the caterpillars are central place foragers, leaving the nest to feed at distant sites.
References
Berger, E. W. 1906. Observations upon the migrating, feeding, and nesting habits of the fall webworm (Hyphantria cunea Dru.) Bull. 60 Bur. of Ent. U.S.D.A.:41-65.
Fitzgerald T. D. 2015. Temporal and spatial foraging behavior of the larvae of the fall webworm Hyphantria cunea. Psyche http://dx.doi.org/10.1155/2015/359765
Snodgrass, R. E. 1923. The fall webworm. Ann. Rep. Smithsonian Institure 1921: 396-414.
Fall webworm caterpillars feed on the relatively dry and tough, aged leaves of the cherry tree. They feed mostly as skeletonizers, removing the soft tissue and leaving the veins behind. (Time-lapse video)
