THE HERMIT CRAB lives alone in the shell of a sea snail. It uses the empty shell after the snail has died. But it may pull out the live snail, getting a new house and a feast as well. Sometimes one crab pulls another crab from the shell it wants.
Unlike other crabs, the hermit has soft, unprotected rear parts. It can thus twist its body into the spiral of an empty seashell. Only its claws remain outside, and it uses them as a tightly fitting door. As the crab grows, it changes its shell for a larger one.
Each hermit crab lives alone in its adopted shell. But large groups of hermit crabs often crowd areas of the ocean floor where seashells are abundant. They can be gathered from pools left after high tide, and make amusing pets. One kind of hermit crab grows 2 feet long. It is called the robber crab and coconut crab because it is said to climb coconut trees and pick the nuts. This crab lives in burrows which it digs beneath the coconut palms of tropical islands. It uses no adopted shell, but has plates of armor on the rear part of its body. It tears coconuts open for food.