Refrigerator magnet features a picture of a hermit crab: HOME IS WHERE THE HERMIT CRABS ARE. 

Hermit Crabs carry around seashells so as to protect their soft bellies.  The shells usually come from snails and mollusks.  As the Hermit Crab grows, it moults, which involves shedding their exoskeleton and finding a new, larger shell to accommodate the larger size.  Hermit Crabs sometimes compete fiercely over a shell.   Their habit of borrowing a shell only big enough for one is why they are called Hermits.  Hermit Crabs may live one to a shell but aren't actually reclusive, living in colonies of 100 or more.

Finding and occupying a shell with roominess is important to the crab's survival because it allows the crab to grow and larger crabs are less vulnerable.  Hermit Crab varieties range in size from 3" to 7".

Of the 500 species of Hermit Crabs, most live in salt water but some are terrestrial.  Terrestrial Hermit Crabs begin life in the water and gradually adapt to breathe air.  They always retain a small amount of water in their shells, however, to moisten their abdomen and hydrate their gills.  One Hermit Crab, the Birgus Latro or Coconut Crab, eschews a shell altogether.   It can crack a coconut with it's pincers and looks altogether too much like a spider on steroids.

Female Hermit Crabs may lay eggs immediately after mating or may store sperm for months.  Eggs are fertilized as they pass through the sperm chamber.  Most Hermit Crabs are born near the ocean shore and do no reproduce in captivity.  After birth, crabs move inland to search for shells to inhabit.  For a young crab, moulting may take place every other month.  When older, moulting takes place in 18-month intervals.  In the wild a Hermit Crab's lifespan is up to 30 years, but pets commonly live only 6 to 9 months.

Magnet is 3" x 3" (7.62 cm x 7.62 cm)