Hermit crab is an animal best known for its habit of occupying the empty shell of a snail. The crab uses the shell to protect its soft abdomen, which it twists into the shell. A pair of small modified limbs at the end of the abdomen grip the interior of the shell tightly. The other walking legs and the claws are covered with a hard, thick material called chitin and usually remain outside the shell. In some cases, a hermit crab can withdraw completely into the shell. It seals off the shell’s opening with one or both claws.
As hermit crabs grow, they exchange their shells for larger ones. A crab usually finds an empty shell to occupy, but it will pull a snail from a shell if necessary. Hermit crabs compete with each other for empty shells in areas where the shells are scarce. Some species occupy holes in small pieces of coral, rock, or wood instead of shells.
Marine hermit crabs often crowd the ocean floor in areas where food and snail shells are abundant. They also live along the seashore in pools left by the retreating tide. Other kinds of hermit crabs spend most of their lives on shore. They often occupy the shells of land snails. One type of land hermit crab is called the coconut crab or robber crab because it feeds on the meat of coconuts. Adult coconut crabs do not occupy shells. In these crabs, the abdomen is curled under the rest of the body.
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