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10:25 p.m. - 2006-03-18
Hermit Crabs!
Greetings, Critter Lovers!

I hope you're having a fun St. Patrick's weekend! Unfortunately I missed out on corned beef, but I guess one can get it year round.

Tonight I had a delightful talk with my budster and former college roommate, CS. She regaled me with stories of her cats, A and KR, and we reminisced about a critter we shared back in the day: My hermit crabs!

Yes, the summer before my (crappy) sophomore year I bought a hermit crab from a vendor in Wisconsin Dells. I named him Macgambit, after a music ear-training computer program! CS reminded me that she never had to use that remedial software!

Anyway, Macgambit moved into my single dormroom, along with my boyfriend at the time, who was not supposed to live there. I was an RA, and the only two arrests on campus that year occurred in my section!

I purchased several other crabs to join Macgambit in the aquarium. At one point I glued a piece of white bunny fur to his shell, to make the crab a "fuzzy pet". Comedy gold!

So, let us learn about the biology of the land hermit crab. These are members of the decapod (ten-legged) crustacean family, which includes sea crabs, lobsters and crayfish. There are about 500 species of hermit crabs, with the majority being entirely aquatic. (Like the one I saw upstairs at my job tonight in a saltwater aquarium.)

In the U.S. the main crabs sold as pets are members of the genus Coenobita: the Caribbean hermit crab, C. clypeatus and the Ecuadorian hermit crab, C. compressus. A picture of the former from

Land hermit crabs are found throughout the world, however, with the largest species living in Oceania. These are about the size of a man's fist, while the tiniest species weigh only a few grams. Here's an anatomical drawing courtesy of

In order to successfully make the journey from sea to land, hermit crabs had to adapt. To survive, their gills changed, becoming firmer, with increased vascularity to transfer gases directly into the body. The gills are kept moist by glands in the bronchial region. Of course, because nature didn't completely protect their bodies with hard chitin, hermit crabs decided to "borrow" discarded shells of various snails and shellfish. They carefully choose shells that will cling to their tiny abdomens quite tightly, in order to keep them moist. Hermit crabs often collect water in their host shell, which they can drink when there is no water nearby.

To drink, a hermit crab extends its claws and draws them up to its mouthparts. Even a dewdrop will suffice, although crabs will submerge themselves to get water, and eat moist foods as well. Hermit crabs are a great clean up crew! They eat everything from plants, carrion, fruit and insects. In Central America they will often feed on animal droppings.

In their native habitat, hermit crabs are often found fairly far from sea. It is thought they avoid the shoreline due to competition from other crabs, birds and other scavengers. They live at altitudes of up to 2300 feet, preferring hard, dry soil.

But for hermit crab love, the crustaceans must go back to their ancestral home, the sea! Apparently there is a very noisy exodus of hermit crabs as they head down to the ocean, usually a week before the full moon during the months of August, September and October. Crab love has never been witnessed! So we must imagine their tenderness together....

Anyway, the females have tiny pleopods, or small legs on their abdomen, (the drawing above shows a male crab; the female has more of the tiny legs down her left side) which they use to clutch anywhwere from 800 to 40,000 eggies! Once the eggs are fertilized, the female continues holding them for a month. At this point, depending on the species, the momma hermit crab will either wade into the water, which causes the eggs to immediately release and hatch, or she will pick up bunches of eggs with her claw, roll them into a ball, and flick them towards the waterline!

The eggs hatch into tiny, free-swimming larvae called zoea. These go through a series of molts and grow for about 40 to 60 days in the ocean. At this point they crawl onto land, where the gills harden, as mentioned above. Unfortunately I don't know if the babies immediately find host shells, or if they have to grow a little before they find shells. Sorry to let you down, critter readers!

But, I do know that hermit crabs make good pets. They are easy to keep, and make clicking noises to each other and interact. I have seen them switch shells, too! It is impossible to forcibly remove a hermit crab from its shell; it will let itself be torn apart rather than let go. But to choose a new shell, the crab will just pull out and back that thing up into the new shell!

Adult crabs go through a molting phase (I don't think mine did) where they will become more inactive and bury themselves for up to a month. During this period they shed their shell, consume the old one for nutrients, and grow another. Obviously they are very vulnerable during this time, and stay buried to preserve moisture. Once molted, a crab may return to its former shell, or pick another. It's important to have a variety of shells available.

This entry makes me want to keep crabs again! Hmmmm. Here's another cute picture from

Well, I hope you'll check these crabs out the next time you're at a pet store!

Clickity click,


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