A crab is a crustacean with an exoskeleton. They can live both in water and on land. Crabs have four to six legs and two large pincher claws. They are scavengers and will eat dead plant and animal matter. Crabs are found in all the oceans of the world and there are also approximately 850 species of freshwater crab. Crabs can be found hiding in rocky crevices and even under the sand or mud. When moving, crabs tend to walk sideways rather than forwards or backwards. Have you ever wondered why crabs walk sideways? Read this article to find out.
Why do crabs walk sideways?
Crabs have a very flat, broad body shape, which contributes to the reason that crabs move sideways. Each crab leg has two joints. The top joint or “shoulder” is restricted by the shell across the back of the crab. The crab can use this joint in its leg to move forwards or backwards but it is very slow and time consuming. The second joint on the crab’s leg is not restricted, but does not bend forwards like human knees. These joints move sideways similar to how our elbow moves when held horizontal to the body. This allows the crab to quickly scurry sideways using this leg joint. Moving quickly is of greater advantage to a crab, because they have many predators. It enables them to quickly slip into crevices and holes to protect themselves.
Some species of crab are able to move forwards and backwards at a quicker speed. These crabs are the raninids, Libinia emarginata and Mictyris platycheles. These crabs have a different body shape to most crabs allowing the “shoulder” joint more freedom when moving.