Great spider crabs look like long-legged spider crabs but are much larger. They are fairly rare in the North Sea. Sometimes they get caught in fishing nets, which is an unusual experience for the fishermen. The crab is dependent upon a disguise since it can't run fast. Young great spider crabs cover their back with torn-off pieces of seaweed. Older animals use barnacles, seaweed or polyps. Should an enemy find the crab despite its disguise, its living disguise sometimes helps to defend the animal.