Snakes, as limbless reptiles, have evolved sophisticated physical mechanisms to navigate nearly every terrestrial environment. They achieve movement not through a single, generalized “slither,” but by employing four distinct modes of locomotion. The specific gait a snake uses depends entirely on the terrain, the required speed, and the space constraints of its surroundings. By applying muscular force and utilizing specialized ventral scales, snakes convert body contractions into forward propulsion across diverse surfaces.
Lateral Undulation
Lateral undulation is the most common and recognizable form of snake movement, often called serpentine locomotion. The snake generates a wave of muscular contraction that travels down the body from head to tail, causing the body to bend into a series of S-shaped curves. This movement requires the snake to push laterally against external anchor points in the environment, such as rocks, blades of grass, or irregularities in the ground. The resistance from these objects cancels out the lateral forces, and the remaining force propels the snake forward along the path established by the head. Specialized ventral scales (scutes) provide higher friction against sideways movement than against forward sliding, enhancing efficiency. This mode is highly effective on rough ground but becomes inefficient on smooth surfaces where anchor points are unavailable.
Rectilinear Locomotion
Rectilinear locomotion is a slow, straight-line movement often employed by heavy-bodied snakes, such as pythons and boas, or when a snake is stalking prey. This method involves minimal side-to-side bending of the vertebral column; propulsion is generated by wave-like movements of the belly skin. The snake anchors a section of its belly scales to the ground using static friction while simultaneously lifting the scales just in front of the anchored section. Muscles move the lifted skin section forward, and then pull the rest of the body forward over the newly anchored section, effectively taking a “step.” This cycle propagates posteriorly down the body, allowing the vertebral column to glide forward at a constant speed while the ventral surface moves in discrete, rhythmic sections, similar to an inchworm. This quiet and controlled movement is also useful for snakes whose flexibility is reduced after consuming large prey.
Concertina Movement
Concertina movement is primarily used for navigating confined spaces, such as tunnels, or for climbing vertical surfaces where other gaits are impossible. The snake uses an alternating anchor and extension pattern. First, the rear portion of the body bunches into tight coils that firmly anchor against the surface, using friction to prevent slippage. While the rear is anchored, the snake straightens and extends its anterior section forward. Once the head and forward part of the body find a new purchase point, they anchor themselves, and the rear coils release their grip and are pulled forward. This is a slow and metabolically costly method of travel compared to undulation, but it provides the necessary static friction and thrust for moving up inclines or through narrow passages.
Sidewinding
Sidewinding is a specialized, highly efficient mode of movement adapted for challenging substrates like loose sand or slippery mud. The snake throws its body in a diagonal, looping motion, moving forward at an angle to the direction its body is pointed. Only two small sections of the snake’s body are in static contact with the ground at any moment, minimizing the surface area that could slip on the unstable terrain. As the head and neck are thrust forward and sideways, the body segments follow, lifting and placing the body down sequentially. This action leaves a series of characteristic J-shaped tracks in the sand, with each track representing a static push-off point. The static contact prevents the sand from flowing away, which is a problem for snakes attempting lateral undulation on loose material. This movement pattern allows desert-dwelling snakes to cross slopes and hot surfaces with speed and minimal energy expenditure.