Hermit crabs fall into one of two basic categories either marine hermit crab that live in the water or land hermit crabs that typically inhabit the shoreline. The type we are talking about here are those that live on land. While the biggest land hermit crab the coconut crab that can weigh up to 9 lbs most kept as pets are considerably smaller.
Hermit crabs are best known for their practice of climbing into discarded spiral sea shells and making themselves at home. Hermit crabs make great first pets. Yes they can pinch if provoked but choosing a smaller crab and teaching proper handling techniques can make this a minor concern. If this is a big concern for you some owners use gloves when handling their crabs. They are also one of the most economical pets you can get.
While there are exotic varieties that are more expensive the two most commonly available species the Ecuadorian Hermit Crabs (Coenobita compressus) and the Caribbean or Purple Pincher Hermit (Coenobita clypeatus) are normally priced under $10.00.
Despite the "hermit" in there name these crabs are actually quite social and tend to be more active if they have a couple of crabby buddies to keep them company. Keeping several together is no more difficult than keeping a single crab and helps to keep things interesting when one of them decides that they need some alone time and stays in their shell.
Housing your hermit crab is also inexpensive as a half dozen or so can normally be kept in a 10-gallon aquarium. Smaller acrylic creature containers are another inexpensive option but the number of crabs kept needs to be adjusted for the size chosen. Any enclosure needs to have enough room for a fresh and salt water water dish a food dish, some cork bark and some branches while still leaving 1/3 to 1/2 of the open for the crab to move around in.
What your crab enclosure contains is actually more important than the container itself as long as it is securely covered and allows you to keep it humid inside. Hermit crabs need a humidity level of about 70% and temperatures in the mid 70's. The main reason for this is that while they live on land they still have gills instead of lungs. These need to be moist or your crab can suffocate. Humidity can be maintained through misting, keeping the substrate moist but not wet, placing a natural sponge in a water dish and covering portions of the top that let air and moisture to escape. Proper humidity is also required when your crab molts.
Temperatures below 70°F or above 80°F can quickly put your hermit crab at risk. Heating the tank is recommended and a heat lamp or under tank heater pad are the two most common choices. Heat lamps can pose significant hazards if not handled correctly so children should never use these. A heating pad should not cover any more than 1/2 of the tanks bottom in order to let the crab roam around and find the temperature that suits them. Placement also plays a big role in controlling temperature. Avoid placing the enclosure near heating and cooling vents, in direct sunshine or directly on the floor as these can all work to quickly raise or lower the temperature into ranges that are dangerous to your crab.
There are a couple of choices for filling the bottom of the tank sand and coconut fiber ("forest bedding" or FB). These can be used by alone or mixed for a more natural texture. No matter which material you use it needs to be 4-6 inches deep to allow the crabs to burrow. Most play sand will work but sand not specifically prepared and packaged for crab or pet use always carries the risk of contamination. Special calcium rich sand is available that can help ensure that your crab gets the calcium it needs to build its shell when it molts. The forest bedding comes in a compressed brick that you soak in water to soften and then crumble for use.
The drawback to forest bedding is that fungus gnats sometimes colonize it particularly if kept too moist and used by itself. Mixing it with sand seems to help as does moistening it with a seawater mix instead of plain water. Using seawater also helps to provide some of the minerals your crab needs. The gnats are not harmful to your crab but they are annoying and not very attractive. If you find them in your crabitat the easiest thing to do is change the bedding although infested bedding can be sterilized by baking in the oven at 300°F for 1/2 hour and letting it cool completely before reusing. No matter what substrate you decide to use it should be moist enough to clump up when squeezed but not wet enough to drip when you put it in the tank.
Once the substrate is in the crabitat its time to add the water bowls one with freshwater and one with a seawater mix should be used to allow the crab to adjust the salts and minerals in its body. Use plastic or glass containers, as crabs are sensitive to metals that are not deep enough to trap and drown your crab. Pebbles or a piece of sponge can be placed in deeper containers to help your crab climb out. Crabs don't tend to be very neat housekeepers so the water needs to be changed daily along with washing out the water and food dishes. The chlorine needs to be removed from any water used by using a dechlorinator product or leaving it uncovered in a wide mouth container for 2-3 days before use.
Hermit crabs are scavengers by nature eating fallen fruit, leaf litter, bark and just about anything that may wash up on the tide so they are not very hard to feed. They will eat fruit, nuts, vegetables, meat, fish and poultry and are generally happy with any scraps you will give them however fatty, spicy or sugary foods should be avoided. There are also prepared moist and dry foods formulated specifically for your crab that helps ensure that all of their dietary needs are met. If fresh foods are fed or given as a treat they should not be left in the enclosure for more than a day to avoid insect problems.
There is more to learn if you plan on being a crabber but these were some of the key points you need to get started. Good luck with your Hermit Crabs!