Crabby crustaceans

Did you know that there are over 4,500 species of crabs? Take a look at some of them.

Have you wondered why crabs always walk sideways? Their legs have joints that only allow them to move that way. It also makes it easier for them to wedge their flattened bodies into rocky crevices to hide from a sharp-eyed raptor in the air.

Walk along the shore and you’ll see a crab vanish in the blink of an eye. This is the Ghost Crab, which can move at incredible speeds. They are box-shaped and often call out from the deep burrows. The noise is a further puzzle. At night, they come out and grab their dinner — tiny fish, algae or other organic matter — from the oncoming waves.

A muted clapping among the tidal pools heralds the Clapping Crab, which raises its front pair of limbs over its head and claps away. This is to frighten away enemies who may make a meal of it. It can be identified by its zig-zag bordered shell.

The Porcelain Crab, with artistic colour patterns on its shell, is a photographer’s favourite. But it is not a true crab. It appears to be a combination of a crab and lobster. When seen head-on, it looks like a crab but has long feelers and an elongated rear body like a lobster. However, its delicate shell breaks easily during territorial fights, as if made of porcelain. When accosted by an enemy, this crustacean doesn’t fight back. It sheds its legs or claws and escapes. The discarded limb keep moving, distracting the predator. And new appendages grow back quickly.

The Hermit Crab does not have a protective exoskeleton for the lower half of its body. So it hunts for an abandoned shell of the right size to fit the vulnerable area. Further, it has to keep looking for empty shells as it grows. But it has devised a clever strategy. Many crabs stand in a queue with the largest being first and the smallest last. Each one steps out of its shell and gets into the larger one of the crab before it. Only the first crab, the largest, has to go hunting for a new shell.

Finally, have you ever heard of the enormous Robber Crab? It measures one metre from leg tip to leg tip and weighs more than four kg. It climbs up coconut trees, uses its powerful claws to rip open the nuts, and helps itself to the kernel inside. Like all crabs, it sheds its shell and grows a new larger one to fit in. But it gobbles up the discarded shell too, reminding us that there is no waste in Nature.

Around 4,500 species of crabs are known worldwide, but there may be so many more yet to be discovered.