A hermit crab is a small crustacean that belongs to the phylum of arthropods. With about 1,400 known species, hermit crabs live either on land, in intertidal areas, or in both deep and shallow waters of the oceans. They are found virtually all over the world, from the tropics to the arctic. The name hermit crab is somewhat of a misnomer, as hermit crabs are social animals that usually travel in large groups.
The most distinctive characteristic of a hermit crab is that it uses the shell of another animal as its home. Most appropriate are the shells of gastropods, usually snails. The hermit crab is not aggressive, and therefore will usually not attack a living snail for its shell unless it is ill. The hermit crab prefers shells that are already vacated.
Unfortunately, some hermit crabs take advantage of manmade objects that pollute the oceans and beaches to make their home. Hermit crabs have been seen dwelling in small jars, plastic casings, or any other refuse that will make do. Experts believe that this behavior is the result of a decline in available gastropod shells. They believe that pollution is causing a decline in the snail population that, along with the practice of collecting seashells, forces the hermit crab to reside in manmade materials.
A hermit crab cannot stay in the same shell forever. The biggest reason that a hermit crab must seek out other shells is because it grows larger, and obviously, the shell doesn’t. When shells are available, many hermit crabs switch shells frequently in their search for the ultimate fit. A hermit crab rarely leaves its shell, but must do so on occasion in order to mate, molt, or move into a new shell.
Hermit crabs use shells because they have an extremely soft abdomen that requires protection from predators. The visible part of the hermit crab consists of a hard exoskeleton, one very large claw that is used for breaking up food and for defense and another relatively small claw used for eating. Both claws assist the hermit crab in its avid climbing. The concealed part of the hermit crab's body has tiny legs that enable it to move when out of its shell and assist in anchoring its body when inside the shell.
Hermit crabs have become a popular pet that is frequently sold or won at seaside boardwalks. They are unfortunately viewed by many as low maintenance, throw-away pets, replacing the traditional carnival goldfish. It is nearly impossible to breed hermit crabs in captivity, as they require the sea to deposit their eggs. For this reason, pet stores and boardwalks must obtain their hermit crabs directly from the wild.