A snake’s movement, often called slithering, is a set of highly efficient mechanical strategies tailored to the environment. Lacking limbs, snakes utilize their elongated, flexible bodies and specialized skin to generate propulsion from nearly any surface. This limbless locomotion allows them to traverse sand dunes, climb trees, and navigate tight spaces with speed and grace. The choice of movement depends entirely on the terrain, ensuring the animal uses the most energy-efficient method for its surroundings.
The Essential Role of Scales and Friction
The foundation for all snake movement lies in the unique structure of its skin, particularly the large, overlapping ventral scales on its belly. These scales are oriented backward, creating a directional difference in friction known as anisotropic friction. This means the resistance to movement is direction-dependent.
The snake experiences significantly lower friction when sliding forward, but much higher friction when pushing sideways or backward. This difference is amplified by microscopic structures on the scales, which act like tiny, one-way hooks. This specialized skin allows the snake to slide easily while providing a firm grip against the substrate when it needs to push off. Underlying muscle groups coordinate with this structure, allowing the snake to create temporary anchor points necessary for generating forward thrust.
Lateral Undulation (Serpentine Movement)
Lateral undulation is the most common and recognizable form of snake movement, characterized by the body forming a series of S-shaped curves. This serpentine motion is primarily used on surfaces that offer numerous external anchor points, such as rough ground, grass, or rocks. The snake propels itself by pushing the outer bends of its body against these fixed objects.
A muscular wave of contraction travels backward from the head to the tail, causing the body to exert force laterally against the environment. As the snake pushes against multiple points simultaneously, the opposing sideways forces cancel each other out. This leaves a net resultant force directed purely forward, driving the snake along the path established by its head. The efficiency of this method is directly related to the roughness of the surface, as more points of resistance allow for greater forward movement.
Specialized Locomotion: Sidewinding and Concertina
Sidewinding
When the ground is too slippery, hot, or loose to provide solid anchor points, snakes employ specialized modes of travel like sidewinding. This method is common among desert-dwelling species, such as the sidewinder rattlesnake, which must cross shifting sand. The snake lifts its body into loops, maintaining only two static points of contact with the ground at any time.
The head is thrown forward and set down, creating a new anchor point while the rest of the body follows diagonally. This action minimizes the body’s contact with the scorching or unstable surface, leaving behind characteristic J-shaped, parallel tracks. The snake progresses by rolling its body sideways, which allows it to move rapidly and ascend slopes without slippage.
Concertina Locomotion
Another specialized movement is concertina locomotion, utilized for climbing vertical surfaces or moving through narrow tunnels. The snake bunches the rear portion of its body into tight, accordion-like curves, which press firmly against the walls or ground to act as a secure anchor.
With the rear section firmly fixed, the snake extends the head and forebody straight forward. Once the front section finds a new anchor, the muscles in the forebody lock into place. The hind section is then pulled forward, collapsing the bunched curves and preparing the body for the next extension. This is a slower, high-effort method, but it is effective because it relies entirely on the snake’s own static grip and muscular strength.
Rectilinear Movement
Rectilinear locomotion is a slow, straight-line movement often used by heavy-bodied species like pythons and boas when stalking prey or moving across a flat, open surface. This mode involves almost no lateral bending of the body. The movement is achieved through the independent, wave-like action of the large ventral scales.
Specific muscle groups connect the ribs to the skin. The snake anchors a section of its belly scales to the ground, using the high static friction of the scales. It then uses these muscles to pull the internal skeleton forward over the anchored skin, much like a tank tread. This process happens in sequential waves down the body, with sections of the ventral skin being briefly lifted and pulled forward before re-anchoring to propel the body.