Timothy Cox, age 12, of Lancaster, Pennsylvania for his question:
How can a snake travel without legs?
The average snake can slither silently along as fast as three and a half miles per hour. Chances are, he can climb a tree or maybe hang by his tail while he swings himself from twig to twig. True, there is nothing remarkable in these everyday gymnastics until we remember that a snake has no legs.
Scientists tell us that a snake travels with a "lateral undulatory motion." Translated, this means that his body remains flat while it waves in sections from side to side. So, if you feel impelled to sketch a traveling snake, make sure that the wavy curves go sideways, and not up and down. This graceful gliding is possible because the snake has a multitude of ribs attached to an extra long supple spine, plus a network of super supple muscles and grippers in his scaly skin.
His spine is a long string of jointed vertebrae. Except for a few at the tail end, each vertebra is attached to a pair of ribs that arch around his snaky body. A four foot long snake may have 150 pairs of ribs and larger snakes have 300 pairs or more. For traveling, the ribs are spread apart or closed in sections. They are spread apart on the outside of each wavy curve and brought closer on the inside.
An intricate muscle system is needed to keep the ribs and spine flowing in smooth lateral waves. Actually it is a super supple sheath, with hundreds of overlapping muscles lying just below the scaly skin. Together they control the wavy spine and the spine controls the curving sections of ribs.
These motions enable the snake to perform his lateral undulatory motion. But they are not enough to take him traveling from place to place.
To get ahead, a traveling snake must be able to grip the ground and push himself forward, section by wavy section. He cannot make any progress across a smooth surface, such as a glass table top, any more than you can march neatly over smooth ice in slippery shoes.
Part of his gripper system is in his body and part is in his natural environment. Some of his scales are small grippers and the lower side of his ribs is attached loosely to his skin. As they spread and close, they form ridges that tend to grip the ground.
The average snake travels flat on the floor outdoors, where usually there are plenty of rough rocks and tufted grasses. He uses these natural objects as pegs and pushes his wavy sections against them. His curving undulations flow forward, first one and then another pushing against this rock and that tuft of grass. When the snake travels, all these separate sections and systems work together in graceful fluid motion.