Animals That Borrow Other Species as Defenses, Disguises, and Shelters

Hermit crabs already borrow one important piece of equipment because their vulnerable abdomens require shells produced by other animals. Some species add another borrowed defense by placing living sea anemones directly onto those shells. The anemones’ stinging tentacles can discourage predators such as octopuses and fishes that might otherwise attack the crab. In return, the anemone receives transportation and access to food particles created while its mobile partner feeds. The relationship can become remarkably persistent. When a hermit crab outgrows its shell and moves into a larger one, individuals of certain species have been observed actively transferring their anemone companions onto the replacement home. That behavior makes clear that the anemone is not simply an organism that happened to settle on a shell. It is a valuable part of the crab’s defensive system. Different hermit crab-anemone associations vary considerably, so the benefits should not be assumed identical in every species.