Animals have evolved an amazing variety of ways to get around. There are animals with no legs; animals with one appendage that serves as a "leg" (snails, clams); animals with two, four, six, or eight legs; animals with dozens of legs; even animals with hundreds of legs. There are animals that move constantly, and animals that stay in one place for their entire adult life. There are animals that swim purposefully and animals that drift wherever the currents take them. Animals slither, crawl, flap, glide, and swim. Some animals spend their entire life underground, whereas others spend almost their entire life in the air. All of these are different modes of animal locomotion.

Locomotion is not the same as movement. All animals move, but not all animals locomote. In ethology, or the study of animal behavior, locomotion is defined as movement that results in progression from one place...