How do snakes move without legs?

Through several distinct locomotion modes, each suited to different terrain — and by exploiting friction that differs by direction, which is the property everything depends on.

Why scales matter. A snake's belly scales are angled so they grip more readily backward than forward. This frictional anisotropy means a snake pushing backward gains traction while sliding forward relatively easily, converting body movement into forward progress.

The four main modes:

Lateral undulation — the familiar S-shaped slither, and the most common. The snake sends waves along its body and pushes sideways and backward against irregularities in the ground: stones, plant stems, roughness. Each contact point provides purchase. This is fast and efficient, but it requires something to push against — a snake on smooth glass can barely move.

Rectilinear locomotion — moving in a straight line without visible bending. Belly scales are lifted and pulled forward in groups by muscles connecting them to the ribs, then set down and pushed back against. Slow, quiet and effective in tight spaces, and used by heavy-bodied snakes such as pythons and boas when stalking.

Concertina — anchoring part of the body while extending the rest, then pulling up the anchor. Used in narrow tunnels and when climbing, where there is nothing to push against sideways but plenty to brace against. Energetically expensive.

Sidewinding — the specialised desert mode. The snake lifts sections clear of the ground and places them down in a rolling motion, leaving distinctive parallel J-shaped tracks. Only two short sections touch the sand at any moment, which minimises contact with hot ground and provides traction on a surface that gives way under sideways pressure.

Some snakes also glide, flattening the body to travel between trees.

Ribs and muscles do the work — snakes have hundreds of vertebrae, each with paired ribs and muscles giving extraordinary control.