I've owned them (properly at least, I owned them about 6 years ago for about a year but they died every few months) for a little over 2 years now. They require much more work than a pet store will have you believe, but in the long run are not that difficult.
They need at least a 10 gallon tank with a lid (they LOVE to climb). I could fit three in a 10 gallon, they were medium sized (slightly larger than a golf ball). Those three are now bordering on large and I have 3 more smalls (ping pong ball size and smaller), these guys are now in a 20 gallon long and it's at capacity as everyone is growing fast.
For substrate they need either sand, 100% coconut fiber (like eco-earth) or a mix of the two. Using only coconut fiber is said to cause some problems with molting crabs so more sand is better. The substrate MUST be moist so that when they dig under their tunnels do not collapse on them. It should be "sand castle consisteny" so you can shove a pencil down into the substrate and have the tunnel you made keep it's shape when the pencil is removed. The substrate should be at least twice as high as your largest crab. They love to dig and need to dig in order to molt.
They need dechlorinated water, both salt and fresh water bowls. The bowls should be deep enough so that the crabs can fully submerge (this allows them to bathe and add water to their shells) and you need to make sure the smallest crab can get out (I use rocks in one end of the bowl). Lots of people use tupperware for water bowls. Salt should be the stuff you use in marine fish tanks, good brands are Instant Ocean and Oceanic. Avoid the hermit crab glub petco sells, it doesn't have enough salt in it.
You should make your own food. Nearly all commercially available foods use perservatives that are potentialy harmful for crabs. Crabs are very sensitive to chemicals. Just chop up some fruit, veggies, meat (VERY important, people often forget they are not herbivores), nuts, eggshell (or cuttle bone)and toss it in a dish. Raw or cooked foods, without seasoning of course.
You need a heating lamp (under tank heaters don't work well under all the substrate and they are not very powerful as side mounts). I use infrared so I don't have to switch between a day and night lamp. You should monitor temp with a thermometer, it should be around 80 degrees Farenheit (5 degrees either way is fine though).
Humidity should be monitored with a hygrometer, it should read 80%, again 5% either way is okay. You'll need to calibrate it as well, I won't go into that unless someone would like me to. Thermometer and hygrometer should be at crab level, not way up high.
They love things to climb on so wood is great. Soak all decorations and substrate in the salt water solution before adding to tank, salt water prevents molding. But to keep the substrate moist in the future you can just use fresh water. Give them somewhere to hide so they don't stress out. Like many animals, stress is a big killer.
Never buy painted shells. The crabs can chip the paint off and eat it, the paint is toxic to them. They do need lots of spare shells. If the crab is in a properly fitting shell then buy shells just slightly larger than the one he's in. If the shell is way to big or way too small you'll have to guess a little about the proper size. Some crabs just like shells that are too big or small though, they'll change if they want to. Boil and then cool the empty shells before adding them to the tank. There should be about 3 shells of the proper size for each crab (this does not mean each crab needs three shells, if you have 2 crabs that require the same size shell you need three shells for the two of them, not 6). I like to rotate shells as well since they tend to like to try on new ones.
They like company, don't keep one by himself.
They molt regularly. Generally they molt by digging under ground and staying there for a while. Their exo skeleton comes off and they are soft. They grow while they are soft and then they reharden. After they are hard again they come back up. Generally big crabs take longer than small ones but also molt less frequently. Not all crabs that are underground are molting, some just like digging and new crabs often go underground to "destress". They have been in poor conditions for so long and have been on trucks and plucked from the wild, if they are in painted shells they have likely been pulled from their natural shells (they are usually gassed or made cold so they go limp)and forced into the painted one, they need some time to rest and calm down. Many new crabs will molt though as in pet store conditions they are usually prevented from doing so with improper substrate (too shallow, dry, or gravel). For all these reasons new crabs are more likely to die through no fault of your own. Generally you should avoid handling new crabs to prevent further stress. Usually once they make it through their first molt they are in safer territory. A newly molted crab will have hairy legs and black tips at the end of his legs.
Anyways, hermit crabs are awesome pets IMO. They are fun to watch, especially when they eat, climb, change shells, or interact with each other. The more you have the more interesting they are. They are capable of living 20 years or more with proper care.
If anyone is interested in owning them send me a PM and I'll send you a link to an AWESOME forum.
/www.hermit-crabs.com/ http
