Hermit Crabs

The animal that carries its home on its back

Hermit crabs evolved from free-living crabs—and some hermit crab species have evolved back into free-living species, including Alaskan king crabs and porcelain crabs. There are over 500 species of hermit crabs around the world, and they’ve evolved a unique body shape to fit into their shell homes. Unlike free-living crabs, their abdomens aren’t covered in a hard exoskeleton but rather a thin, soft one; their abdomens are also twisted to fit the spiral cavity of the snail shells in which they make their homes.

Opportunistic eaters


Hermit crabs are pretty easygoing about what they eat. In fact, they’ll dine on just about anything they can find in the water that surrounds them, including small fish, invertebrates such as worms, plankton and any food particles that happen to be floating by.

 

Delicious morsels


Hermit crabs are also high on the list of desired foods for many predators. Fish such as pricklebacks, gunnels, clingfish and snailfish prey on hermit crabs, as do sea stars, larger crabs, gulls and crows.

Aggressive house hunters


Contrary to popular belief, hermit crabs don’t kill the snails in whose shells they make their homes. They’re actually able to smell dead or dying snails, which can lead them to a potential shell. But competition for such shells can be fierce. Hermit crabs may fight to the death in pursuit of a shell. And, as they grow, they must seek out new shells in which to live.

 

Night owls


Hermit crabs are nocturnal, which means they’re much more active at night than they are during the day. To see them scuttling around, visit a Puget Sound tide pool at night during a low tide—be sure to bring a flashlight! You can also see hermit crabs at the Seattle Aquarium, in our Life on the Edge exhibit.

Not truly hermits


Contrary to their name, hermit crabs aren’t solitary creatures. In the wild, they’re found in groups of 100 or more. Social behavior in hermit crabs is also sometimes observed during mating, when the male may stroke and tap the female’s claws—or grab her shell and carry her around!—before mating begins.

Other Invertebrates


Giant Clams

Giant clams stay permanently attached to the same spot for life.

Corals

You can see both warm- and cold-water corals at the Seattle Aquarium.

Sea Star

Sea stars don’t have brains but are still able to detect light!

Sea Anemone

These creatures can survive at depths of more than 32,000 feet.

Moon Jelly

Jellies have been around for hundreds of millions of years!