Hermit Crabs are sort of a quirk in the crab world. They have a hard exoskeleton on their front end with claws that are very crab like. Their rear end, however, remains soft and coiled to fit into a snail shell. You will only see these crabs without a shell if they are "house hunting" or stressed out by heat or close quarters. They can walk in and out of a snail shell with ease once they unhook their attachment on the tippy-tip end of their abdomens.
It is a cardinal rule of observing Hermit Crabs that one should never try to pull the animal out of their shell. They will in all likelihood break in half, which would be a very sad situation indeed. If you really would like to see the "whole animal" out of a shell, there is a way to trick it into walking out peacefully. Just find a Hermit Crab and provide it with an empty snail shell of about the same side as its current abode. Given a chance, the crusty animal will become curious and will try the new "house" for size. The change of housing may happen quickly so keep a keen eye out for its behavior. Always, the crab will slip its soft abdomen in first. Any soft parts left unprotected will provide choice nibbling for any crabs, Hermits or otherwise.
So leave it to say that Hermit Crabs come out of their shells naturally for a few good reasons: their current house is a too tight fit; it's too hot in their shell (they may be left stranded in the sun); or the animal is stressed. If you collect too many of these animals in a small bucket, they may get confused and walk out of their shell. Sometimes, these animals may get in fierce fights that end up in the demise of one combatant. The victor may quietly eat the vanquished .
What do these animals eat (naturally)? Like most crustaceans, they eat whatever is available - smaller animals, soft crabs, worms, clam siphons, fish, shrimp, sea vegetables, you name it. They even climb into lobster traps to dine on the bait left for lobsters!
How big do they grow? Moon Snails can be found to fill one's hand. An empty shell provides housing for these large adult Hermit Crabs. These animals, however, will not attack a live snail to get a new house. They just look around for an empty one after the snail dies. A Hermit Crab, however, will fight another Hermit fiercely over an empty shell. Sometimes these shells are crusted with barnacles, algae and limpets. You may find Hermits with a coating of "pink fur". These crabs have an animal colony growing on their shells. The "fur" is actually made up of hydroids, a stationary relative of jellyfish. As long as it is an empty shell, it doesn't have to be beautiful. After all, in a pinch, any shell is a castle even if it is a little snug or too roomy.
Hermit Crabs are either male or female. They mate after molting, though both animals remain partially in their shells. The female broods the eggs inside her shell, though attached to her body. Periodically, she comes out of her shell to aerate and clean the eggs. The eggs develop into planktonic larvae that swim free of the mother and undergo several changes before settling to the bottom where they search out small shells for protection. And then, if all goes well, they start a parade of ever-changing portable houses.
One of my favorite books on these creatures is a classic by Holling Clancy Holling, PAGOO. Ask your library to locate it for you. You will not only learn a lot about Hermit Crabs, but about many other creatures you may encounter in salt water forays. The title, Pagoo, is a shortened version of the animal's scientific name, Pagurus. Have fun!
Ronnie K., 7/14/00