Crabs of the family paguridae and coenobitidae. Most crabs have a hard shell covering their whole body and four sets of walking legs.
Hermit crabs have only three pairs of walking legs, and lack the hard covering on the rear portion of their body, and so use empty shells to protect themselves (although in some areas,
hermit crabs don't use shells at all. Rather they will live in plant stems, sections of
bamboo, broken
coconut shells, hollow pieces of
wood,
coral or
sponge).
Hermit crabs occur all over the world, and live in
water, on
land (like the variety often kept as a
pet), or sometimes even in
trees.
The
hermit crab has four pairs of
legs, the front-most of which form
claws. The claws they serve not only to aid in scavenging (
hermit crabs are
scanvengers and eat almost anything), but also to block the entrance to their
shell. The right
claw is usually larger and the
body of the
crab usually curls to the right (to fit the curvature of the shell). The rear-most pair of legs is used by the
crab to
grip the central column of the
shell. Only the middle two pairs of legs are used for
walking.
When a
hermit crab outgrows a shell, it will leave its home in search of a new one, often removing the current
occupant with its claws. Many animals may live upon the shell (such as
sponges or
sea anemones), feeding on what the
hermit crab spreads about. When the
hermit crab finds a new home, it is common for the animals on the old shell to move onto the new one, or for the
crab to actually
transplant the creatures himself. these animals serve as
camouflage.
In the wild,
hermit crabs are usually found in groups of about 25. If kept as pets, they do best in groups. In the wild,
hermit crabs can live up to 25 years and attain huge sizes, but in
captivity they will usually live less than a
year, though with good care they may live to four years old.
references: www.britanica.com, http://www.xs4all.nl/~pal/hermit.htm, http://www.york.biosis.org/zrdocs/zoolinfo/grp_crus.htm, http://www.mov.vic.gov.au/crust/hermgall.html