Hermit crabs are just one of twenty-five thousand types of crustaceans in the world, but they are unique in that they live in empty snail shells, carrying the shells with them not only as shelter but also as storage facilities. These fascinating creatures are easy to keep as pets; they're a good choice for children who are old enough to care for and appreciate living creatures.
Hermit crabs require relatively simple habitats. If you choose to adopt a one, you'll need a glass tank filled with 2 to 3 inches of sand and smooth gravel at the bottom (Marc prefers sand meant specifically for marine aquariums). Install an under-tank heater so the temperature can be kept at about 75 degrees. Since hermit crabs are nocturnal and don't like bright lights, use a red bulb for your heat lamp. They also require a steady level of humidity, so their sand should be misted with chlorine-free water every day. You can buy a humidity gauge at a hardware or pet store to make sure the humidity level stays between 50 to 70 percent. Inside the tank, place some coral branches and plastic plants, as well as a nonmetallic water dish that's shallow enough for the crab to climb in and out. You may even want to consider adding a small sponge inside the dish to serve as a "step ladder." Hermit crabs can eat any of the prepared hermit crab foods, but enjoy an occasional treat of fresh fruit and peanut butter.
People commonly keep one of two hermit crab types: the purple claw crab and the smaller Ecuadorian crab. The Ecuadorian is usually more active than its cousin and requires salt water (purple claw crabs do fine with fresh water). Make sure to add a salt mix intended for salt-water aquariums to their water, and never use water with chlorine. Keep the tank clean, and change the water daily. Once a week, you should rake the sand and remove any waste from the bottom. If you discover your crab has burrowed into the sand and doesn't come out, chances are it's molting. This is a natural process, and it's a good idea to leave them alone for a few weeks until the molting is complete.