Greg Nelson, age 12, of San Francisco, California, for his question:
How does a snake move?
Scientists say that a snake travels with a lateral undulatory motion. Translated, this means that his body remains flat while waving from side to side. However, there is more to his complex motions. A snake also can rear up to strike his prey and swim almost as well as a fish and chances are he can climb a tree. True, there is nothing remarkable in these actions until you remember that he has no legs.
The sidewinder progresses with a looping motion that may appear clumsy. But the motion of other snakes is very graceful, no matter what you think about snakes in general. The sinuous gliding is possible because of special ribs and spine, a network of supple muscles and certain features of the scaly skin.
The spine is a string of jointed vertebrae and, except for a few at the tail end, each is hinged to a pair of arching ribs. A four foot long snake may have 150 pairs of ribs and larger snakes have 300 pairs or more. Under the skin, a network of smooth, overlapping muscles move to curve the supple spine from side to side. The snake crawls flat on the ground with a wavy motion and each section of his long body follows inch by inch through the same curves, somewhat like a stream meandering down a well worn channel.
However, this graceful swishing from side to side is not enough to move him forward. In order to progress, he needs to get a good grip on the ground and push against solid objects. His natural environment solves this problem free of charge. The ground is strewn with bumpy stones and rough tufts of grass. On his underside, each pair of ribs is attached loosely to a pair of scales. As his spine curves, it moves his ribs and they ripple his skin in a series of ridges along his underside.
These ridges act as grippers to hold and push against the obstacles in his path. This shoving operation goes on out of sight and he appears to glide gracefully forward with no effort at all. However, the shoving it vital to his progress.
If transferred to a glass table top, for example, there are no small objects to grip. When he swishes from side to side, he slithers all over the place and gets nowhere. This is similar to what happens if you try to walk across a stretch of slippery ice in a pair of slippery shoes.
The snake's method of travel has many advantages in his way of life. He is, of course, a meat eater, and most of his victims can move faster than his three¬mile an hour limit. His best chance is to sneak up on them and catch them by surprise. This he does by traveling silently, close to the ground. As his supple body slides through his lateral undulatory motion, not even a blade of grass is disturbed.