There are land hermit crabs and aquatic hermit crabs. Land hermit crabs, as you might guess, live on the land, and aquatic hermit crabs live underwater in the ocean. :) I'm assuming you are asking because you have a pet hermit crab. All hermit crabs sold as pets are land hermit crabs.. which is actually kind of a misnomer, considering they really like to spend most of their time in trees. :) Any hermit crab you find on the beach in the US is most likely an aquatic hermit crab that would need a saltwater tank set-up to survive. All hermit crabs you find being sold in pet stores or on the boardwalk are land hermit crabs. :) If you have any questions about a land hermit crab pet, the link I provide is to Florida Marine Research, which is where the majority of pet hermit crabs sold in the US come from.