Snakes live in a wide variety of habitats – terrestrial, arboreal, aquatic and fossorial (underground). They also vary in size from the world's smallest snake, a recently discovered Barbados threadsnake, which measures only 10 cm, to the world's most massive snake, the Green Anaconda, which may grow to 9m and weigh 220 kg. Apart from a few adaptations the structure of all snakes is basically the same – a limbless, cylindrical, scale covered body.
Animal locomotion is governed by Newton's third law of motion - to propel itself forward; an animal must push something backwards. In many animals limbs such as legs, fins, flippers, tails and wings are used to push against the surrounding environment of ground, air or water in order to achieve propulsion. In snakes a flexible skeleton, powerful muscles and strong scales are used to the same effect.
There are 5 modes of locomotion that snakes may use:
Lateral undulation or slithering is the most common serpentine locomotion. The snake undulates its body and the bends of the snake push off against the points of contact in a coordinated, sequential muscular activation, which propels the snake forward.
Sidewinding is the fastest locomotion, but is only used proficiently by some species eg the rattlesnake. The head, tail and midbody are lifted and dropped on a diagonal course with only 2 portions of the snake having contact with the ground at once.
Concertina is used for climbing and moving in narrow spaces. The snake pulls its body into bends then straightens out forward from the bends, anchors itself then pulls its body up into bends again.
Rectilinear is a slower form of locomotion used by large snakes and it allows the snake to move in a straight line. Muscles that connect the skin to the skeleton raise the belly scales above the ground, the ends of the scales stab downward into the ground then are moved backward as the body travels over them, this happens at multiple points along the body.
Slide pushing is an irregular, ineffective mode of locomotion usually used when the snake is trying to escape and it is not a well understood form of locomotion.
By utilising the combination of these forms of locomotion snakes can travel over all types of land surfaces, climb trees, burrow and swim.
The most incredible snake locomotion is that of the flying snakes of South and South East Asia. These tree snakes achieve flight by flattening their body and using longitudinal hinges on their ventral scale which create a cavity that slows their descent. The snakes jump from trees into the air then flatten themselves and glide to another tree or to the ground. It had been thought that they were simply parachute flyers but recent studies have revealed that their body is used more as an airfoil than a simple parachute and that their flying technique is far more sophisticated than originally thought.