House-hunting Hermit Crabs

Forced to move each time they outgrow their homes, hermit crabs have mastered the art of house hunting.

Unlike their hard-shelled relatives, hermit crabs have soft, vulnerable abdomens. To protect their bare bellies from predators and rough rocks, they haul around in hand-me-down snail shells, upgrading to larger models as they grow. Due to a chronic shortage of good real estate, finding a new shell can be a struggle, particularly since each hermit crab species prefers a specific type of mobile home. These Blue-handed hermit crabs (Pagurus samuelis) favor the secondhand homes of black turban snails, while other hermits seek out the shells of separate snail species.

To find a new home, hermit crabs rely on both their eyes and their pincers. The latter are lined with receptors that can detect the presence of calcium - one of the basic building blocks in seashells. By using these sensitive appendages, the crabs can identify even predominantly buried shells as potential homes. Once they find a viable shell, they vigorously probe the opening to check for other inhabitants. They will fight with other crabs over a desirable house, but they'll back down if the tenant is a snail.

Since recent human activity has increased the shortage in shell housing, some hermit crabs are getting creative with their house hunts. A recent scientific study showed that hermit crabs in the Pacific and Indian Oceans are swapping natural shells for cast-off pieces of plastic and glass, turning one man's trash into a hermit crab's treasure.

Even a bottle cap can serve as home sweet home.
Blue-handed hermit crabs (Pagurus samuelis) prefer to wear the hand-me-down shells of black turban snails. Photo: Gerald and Buff Corsi, Manzanita/CAS Special Coll.
In the hunt for a perfect house, one hermit crab may try to evict another from its shell.
Photo: Gerald and Buff Corsi, Manzanita/CAS Special Collections