Look a little closer
Geckos do not climb walls with suction cups or wet glue. Dense microscopic hairs under their toes bring vast numbers of tiny contacts extremely close to a surface, allowing weak intermolecular attractions to act together.
Ridges on a toe pad carry many hair-like structures called setae. Each seta branches again into hundreds of much smaller, flattened tips known as spatulae. This hierarchy conforms to fine surface contours and greatly increases real contact area.
When molecules in two materials approach closely, fluctuations in charge distribution can produce weak attractions called van der Waals forces. One contact contributes little, but the combined interaction of enormous numbers of spatulae can support the animal's weight.
Directional control explains how a foot can hold strongly and still release during every step. A gecko places a toe and pulls so the hairs lie in their gripping direction. To detach, it changes the angle and peels the toe upward from its tip, reducing contact much like lifting the edge of tape.
Not all gecko species have identical adhesive pads, and surface conditions matter. Dust, water and very rough textures can interfere with close contact. Experiments also show that some gecko setae shed contaminating particles during repeated steps, giving the system a degree of self-cleaning.
The adhesive is therefore a triumph of structure rather than a special glue. A branching design from toe to hair to nanoscale tip gathers countless weak molecular forces into a grip that the animal can switch on and off rapidly.
