Bert Whetstone, age 7, of Sarasota, Florida, for his question:

Why doesn't a crab walk forward?

Sometimes he does, though you just may not be there to see him do it. That same crab can walk forward or backward, sideways or in any other direction, when he wants to. And the amazing fellow can change his direction without turning his body around. Most animals like to see where they are going. But the crusty old crab does not seem to care about this at all. Perhaps this is because he has eyes on moveable stalks, fixed on top of his head.

Every animal gets around the best way he can. Birds that fly well cannot gallop because they have wings instead of front legs. They are built to hop around on two legs and fly through the air with the greatest of ease. Most fast runners have four legs and strong muscles to make them go go go. The kangaroo manages to go just as fast on his two mighty back legs which are made for leaping. The snakes have very elaborate ribs and muscles to slither along without any legs at all.

A crusty crab has ten legs. The two front ones are his fierce pincers. He uses them as a knife and fork to stuff food into his mouth and also as weapons to pinch his enemies. His other eight legs are meant for walking around. However, he has a very wide body, and it is encased in an unbendable shell. This makes it easier to walk sideways and, like other animals, he tends to get around in the most comfortable way.

This does not mean that this is the only way he can go. It so happens that there are many joints in his walking legs, and he can bend them this way or that. When something interesting is in front of funny face, he walks forward. Sometimes he backs away into a sheltered corner. Perhaps these directions make him feel rather clumsy. As a rule, he uses his walking legs to scramble along sideways, in any direction he plans to go. If you watch him for a while, he may pause a moment and then set off in the opposite direction. He can do this without turning himself around.

Scientists have found and named about 4,500 different crabs. And all of them seem to feel more comfortable walking sideways. The smallest ones are tiny enough to hide in oyster shells. The giant is the Alaska king crab, who may weigh 12 pounds. All sorts of medium sized crabs live on our beaches, scrambling sideways over the rocks and the sand. All of them have gills to take oxygen from the water and some have specially flattened legs for swimming in deep water.

Each crusty crab has his own way of life. Though they all need water, some of them spend a lot of their time on the land. Ode find them scuttling in and out of marshy swamps or far inland from the sea. One crab has learned to climb trees  because he enjoys eating the coconuts that grow at the top of tall palms. As a rule, he claws his way up and down in a sideways direction    because this is his natural way to walk.