One of the best entertainment for a person relaxing on the beach by the sea is to watch crabs. These representatives of the class of crustaceans amuse people with their habit of moving not forward, but sideways.
The question of the reasons for this way of movement of crabs, as well as why crayfish move back, has occupied people since ancient times. Even a legend was born about how the crab and the crab accompanied the sea king on a walk, and when he met a shark, the crab, frightened, recoiled back, and the crab retreated sideways into the nearest thicket of seaweed. The sea king punished both subjects for cowardice, forcing one to back away all his life, and the other to walk sideways.
Of course, a modern person will not be satisfied with such a fabulous explanation.
Crab anatomy
Crabs have very long and powerful legs, which are slightly turned forward. Thanks to this, the joints cannot rise above the abdomen. This is very important for an animal that spends most of its time in shallow water and has many natural enemies. In case of danger, it is easy for a crab to lie flat on a sandy bottom, without attracting attention, or quickly hide under stones.
But for such a structure of the limbs, the crab has to pay by the fact that it can develop the greatest speed when moving sideways. When speed is not critical, the crab can walk in any direction, but when it senses danger, it seeks to escape and begins to move in the most convenient way for it. This does not interfere with monitoring the source of danger, because his eyes are on the stalked outgrowths, which creates an all-round view.
There is another reason to move sideways in case of danger. The claws of the crab, like the hands of humans, are asymmetrical - it is easy to see this by looking at it: one of the claws is larger than the other. As in humans, the leading claw in most individuals is the right claw, with which the crab grabs food, and with the left it defends itself if necessary. Running away from someone dangerous, he covers himself with a "protective" claw, and this is also more convenient to do, moving sideways.
Cancer moves backwards
A close "relative" of crabs, crayfish, also has an interesting peculiarity of movement. This animal swims with its tail forward, since it is in this direction that the body of the crayfish has the most streamlined shape, and when moving in the opposite direction, large pincers would interfere.
Cancer can walk in any direction, but it develops maximum speed when moving backwards. At the same time, the tail bends under the abdomen and throws out a stream of water, which "works" on the principle of a jet engine, increasing the speed of movement of the animal.
The crab does not always walk sideways, and the crab moves backward - both do this only in case of danger. Animals perceive a meeting with a person as a danger, therefore people most often observe just such a movement of crabs and crayfish.
