Spider's foot. Coloured scanning electron micrograph (SEM) of a spider's foot, showing claws, and gripping and sensory hairs (setae). The claws on a spider's feet are used to grip rough surfaces, while the setae (white) are used to grip smooth surfaces. These setae enable the spider to cling to smooth surfaces by taking advantage of weak intermolecular forces, known as Van der Waals forces. The longer hairs (yellow) are sensory structures. This is a foot of the jumping spider Myrmarachne formicaria. Magnification: x265 when printed at 10 centimetres across.