The giant hermit crab is the largest marine hermit crab in North America. Its carapace (external skeleton) is red or purple with noticeably large, scale-like bumps. Like other hermit crabs, this species has a soft tail and uses an abandoned snail shell as its protective mobile home. Small tabs along the crab's bottom help it maintain a grip inside the shell so that it can recoil inside for protection. As the hermit crab grows, it must find larger shells to occupy. Hermits are generally secretive when changing shells due to their vulnerability to predators during that process.