They rely on the mother crab to give birth to small crabs, and every time the mother crab will lay a large number of eggs, the number can reach more than one million. After these eggs hatch in the abdomen of the mother crab, the larvae can leave the mother and float around with the coastal current. After molting several times, it grows into a big-eyed larva, and after molting several times, it grows into a young crab. The appearance of a young crab is almost the same as that of an adult crab, and it becomes a crab after molting several times. Most sea crabs are directly discharged into the sea without hatching after their eggs mature.

The hard carapace of crabs can protect crabs from natural enemies, but the carapace will not expand with the growth of the body. Therefore, the growth of crabs is intermittent, that is, after a period of time, the body will continue to grow after the old shell falls off. The largest crab on the earth is the spider crab, with a foot width of 3.7 meters, and the smallest crab is the bean crab, with a diameter of less than half a centimeter.

Although the crab is small, it covers everything. After removing the hard shell of the crab, we can find that the body part of the crab is protected by a shell. These shield-like shells are called crustaceans by biologists. Crabs are symmetrical and can be divided into forehead area, eye area, heart area, liver area, stomach area, intestine area and gill area. The two sides of a crab are connected by appendages. The appendages of the head are called tentacles, which have the functions of touch and smell. Some appendages have the function of mouth, which is used to tear food and send it into the mouth.

Crab chest has five pairs of appendages, which are called chest feet. A pair of appendages at the front end are equipped with powerful claws, which can be used for foraging. The other four pairs of appendages are crab feet. Crabs rely on these four pairs of appendages to walk and move. The way they walk is unique and interesting, and most of them walk sideways rather than straight. Except monks and crabs, they all walk straight.

Crabs spend most of their time looking for food. They are not picky eaters and eat whatever their claws can catch. Small fish and shrimp are their favorite, but some crabs eat seaweed and even animal carcasses or plants.

Crabs eat other animals, and other animals may eat crabs. For example, humans regard crabs as delicious food. And waterfowl eat crabs! Some fish like to eat crab feet as much as humans. When young crabs and underage crabs float in the sea in groups, they may be devoured by other marine life, so crabs have to lay a lot of eggs when laying eggs.

Fiddler crabs are common crabs on the seashore. Why is it called fiddler crab? Because these crabs wave their claws as if they were waving in the tide, that's how they got the name "Zhao Chao". In addition, the giant claws of male fiddler crabs seem to play the violin, so they are also called fiddler crabs or piano crabs.