Hermit crabs socialize to evict their neighbors
Social animals usually congregate for protection or mating or to capture bigger prey, but a University of California, Berkeley, biologist has found that the terrestrial hermit crab has a more self-serving social agenda: to kick another crab out of its shell and move into a larger home.
All hermit crabs appropriate abandoned snail shells for their homes, but the dozen or so species of land-based hermit crabs are the only ones that hollow out and remodel their shells, sometimes doubling the internal volume. This provides more room to grow, more room for eggs and a lighter home to lug around as they forage.
But empty snail shells are rare on land, so the best hope of moving to a new home is to kick others out of their remodeled shells.
When three or more terrestrial hermit crabs congregate, they quickly attract dozens of others eager to trade up. They typically form a conga line, smallest to largest, each holding onto the crab in front of it, and, once a hapless crab is wrenched from its shell, simultaneously move into larger shells.