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A white wave shape.

Hermit crab

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.

At the Aquarium

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 habitats.

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.

Quick facts

Hermit crabs sport a soft exoskeleton and a twisted abdomen to fit into snail shells.

As they grow, these creatures look for another empty shell to move into.

Little but fierce! Hermit crabs may fight to the death in pursuit of a new shell.

Explore More Invertebrates

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Two sea otters at the Seattle Aquarium floating on the water in their habitat, holding onto each other demonstrating a rafting behavior.

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An adult sea otter at the Seattle Aquarium looking upwards with its front paws resting on its front.

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Sea otter at the Seattle Aquarium laying on its back, raising its head and front paws.

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