How Does a Hermit Crab Move?

Anyone who has seen a hermit crab scuttle across a beach or an aquarium balancing a heavy shell on its back has likely wondered: How does a hermit crab move? Like other animals that rely on shells for safety and protection from predators and the elements, hermit crabs' bodies are designed to move quickly when necessary, even while wearing large shells.

  1. About Hermit Crabs

    • Hermit crabs are common on beaches in the eastern United States and around the world. They are easy to catch and are popular pets, particularly the land variety, which are hardier and require a less specialized habitat then the saltwater hermit crab. Because they do not have shells of their own, they are not considered to be true crabs.

    Anatomy

    • Understanding how a hermit crab moves requires a basic understanding of hermit crab anatomy. Hermit crabs are decapods, which means that they have 10 legs. Two of a hermit crab's legs are actually pinchers or claws. The left claw is larger then the right one.

      On each side of its body are four visible legs called "walking legs," which are designed to grasp surfaces and provide traction and speed. The back legs are usually hidden and are designed to hook onto the hermit crab's shell, anchoring the crab securely inside of it and allowing it to support the weight of its shell on its backs.

    The Right Shell

    • The hermit crab's ability to move quickly in a straight line as opposed to scuttling sideways like most "true crabs" is partly because when it's attacked or threatened, it can quickly stop and fold itself into its shell, unlike crabs that must continue to run while preparing for a fight or to attack at the same time.

      If a hermit crab chooses the wrong shell, however, the ability to move quickly and hide from predators is reduced. If the shell is too large, the crab's back legs may not be able to hold it to the body as securely, forcing the crab to move more slowly so that it does not fall out of its shell completely. If a shell is too small, the crab's body and legs will be cramped, and movement, whether fast or slow, will be difficult. Always make sure that your pet hermit crab has a wide selection of shells to choose from as it molts and grows.

    Climbing

    • Land hermit crabs are also good climbers, using their claws and walking legs to hold tightly to branches and other surfaces and their back legs to hold their shells in place. For this reason, land hermit crabs are also sometimes referred to as tree hermit crabs. One species of hermit crab in particular, the Coconut or Robber Crab, spends the majority of its time in trees.

    Considerations

    • If a hermit crab loses a limb, its walking ability will be impaired until it is able to molt and regenerate the missing appendage. When handling hermit crabs at home or in the wild, never grab them by the claws or legs, and never try to pull them out of their shells.