The crabs were evidently at one time close friends of humans, as is suggested by the humans who were known to live near the largely inaccessible Crab Castle. However, High Roller persuaded Crab King and his subjects to turn on the humans, and the crabs began abusing humans by burying them in sand.
Around the time of "Crab Castle", the humans managed to send a message in a bottle, which floated to Big Green, telling of their plight. A team, aided by new recruit Sammo Whale, was then dispatched to confront the crabs. The two met in aquatic battle, where Big Green became the clear victor when the crabs were all caught in a large fishing net. The crabs, however, refused to surrender unless their king could be beaten in a sand sculpture competition.
Lin Chung accepted the responsibility of this competition, and managed to defeat Crab King. Accordingly, the crabs surrendered and sided with Big Green. They subsequently built an underwater home for Sammo. Crab King was also known to remain at Big Green, where he would give aid when his strength and earth-moving capabilities were needed, such as in "Pitched Battle of the Great Wall Train" and Cheetah Castle II. He also helped to form the Bronze Giant in "The Bronze Giant".
Most crabs are relatively small, with multiple legs and squarish bodies. They come in a variety of colors. They have two claws of equal sizes and dark beady eyes atop stalks.
Crab King is sgnificantly larger, and possesses one bigger claw which resembles a backhoe shovel.
Crabs are capable swimmers, even without fins or flippers, and can breathe underwater. They can shovel sand with their claws, and some are known to be gifted and speedy sand sculptors. Crab King demonstrated great strength, as well.
- The language of crabs consists of the sounds of snapping their claws rather than speaking. When Commander ApeTrully speaks the language, he presses his fingers together and says "click."
- A small crab sits on and pinches Red Face Kwan's buttocks, causing his red face. It is first seen in "Lion Castle".