Caterpillars Recruit Friends with Anal Scraping

Newly hatched caterpillars look helpless: they're teensy, soft and juicy, with no parent around for protection. But certain young insects, the masked birch caterpillars, are more capable than they seem. They gather in groups to keep themselves safe. To form those groups, they use a previously undiscovered language of buzzes, vibrations, head banging and butt scraping. The species, Drepana arcuata, passes through five caterpillar life stages (called instars) on its way to becoming a little beige moth with hooked wingtips. As a caterpillar it resides, and munches, on the leaves of birch and alder trees across North America. The older caterpillars live alone. When they encounter each other, they may fight over shelters they've built from silk; during these disputes, they signal to each other by vibrating. Younger masked birch caterpillars, on the other hand, are friendly. They live in groups during their first and second instars. This is probably ...