Hermit crabs are not considered true crabs. This is due to their unprotected abdomens. This is why hermit crabs carry shells on their backs that they have found laying around to protect themselves from predators. Hermit crabs are omnivorous (scavengers). Not only do they grab any shell they can find that they can fit into, but they also find food wherever they must from plant and animal matter and such. They nibble from other shells such as the sand dollar, sea biscuit, and coral, for added calcium that is necessary for them come time for molting. They eat from plants and scour the ground for any meat that is left along the ground. Their diet is of a wide variety of foods, but if you get one for a pet it is best to not allow them to eat dairy, or many sugary cereals and such. More about feeding hermit crabs as pets can be found in the Pet section.