Hermit Crab Swarm

When hermit crabs find a shell that is too large, they lie in wait for others to arrive and move into the shell, abandoning a possible replacement. This can form a large chain of queuing crabs waiting to upgrade their shells. Interruptions can aggravate the crabs, resulting in attacks against the unfortunate source of disruption.

Hermit crabs have hard exoskeletons like other crabs, but with much weaker abdomens. They find and "wear" shells as homes and protection, getting around with their front legs and claws. Surprisingly fierce, hermit crabs fight for new shells as they grow bigger, using an assortment of hollow alternatives as substitutes when shells of the right size can't be found.