Hermit crabs use their shells to hide from predators like seagulls, larger crabs, sea stars and snailfish. These animals are at their most vulnerable when they leave one shell for another, which they must do as they grow because their shells do not grow with them. However, some predators can either bite through the hard shell or pull the crab out and eat it.
Fish such as gunnels and clingfish count among the hermit crab's predators, but these crabs aren't safe once they leave the water. Birds such as crows and land animals such as raccoons also prey on these small animals. Hermit crabs use shells for protection, and according to Scientific American, they can hollow out too-small shells to allow for more room to grow. However, these hollowed-out shells are easier for predators to crush.
According to Smithsonian Magazine, hermit crabs can also be cannibalized by their own kind. Researchers have shown that these animals, rather than being repulsed by the smell of dead other hermit crabs, are actually attracted to the smell. This puts them in danger of predation from the same animal that killed the crab that released the scent, but they can also end up getting scraps to eat in exchange for the risk.