How do geckos stick to walls?

Short answer: geckos do not use glue, suction cups or a sticky liquid. Their toe pads carry huge numbers of microscopic hairs called setae. Each seta branches into even smaller tips called spatulae. When those tips are brought extremely close to a wall, weak intermolecular attractions—especially van der Waals forces—act across an enormous number of contact points at once.

One weak force becomes powerful in parallel

Van der Waals forces between individual molecules are tiny. A gecko solves that scale problem with surface area. Instead of pressing one smooth pad against a wall, it divides contact across millions of fine structures. The classic PNAS experiments showed that isolated gecko setae adhere strongly even to surfaces with very different chemical properties, supporting van der Waals attraction rather than a glue-like secretion or capillary suction as the main mechanism.

The feet are directional, not permanently sticky

A gecko also has to let go in milliseconds. The hairs work best when loaded at particular angles. By rolling and curling its toes, the animal brings many spatulae into close contact and loads them in a direction that produces high adhesion and friction. To detach, it changes the angle and peels the structures away, a little like lifting tape from one edge rather than pulling the whole strip straight off.

Why it can run instead of getting stuck

The attachment-detachment cycle is fast enough for geckos to sprint on walls and ceilings. The system is therefore better described as a controllable dry adhesive than as a permanently sticky foot. Surface roughness, contamination and moisture can change performance, and different gecko species are adapted to different surfaces.