This is the first time anyone has measured exactly how spiders stick to surfaces, and how strong the adhesion force is. The team used a scanning electron microscope (SEM) to make images of the foot of a jumping spider, Evarcha arcuata (pictures available see notes). There is a tuft of hairs on the bottom of the spider's leg, and each individual hair is covered in more hairs. These smaller hairs are called setules, and they are what makes the spider stick.
The paper reveals that the force these spiders use to stick to surfaces is the van der Waals force, which acts between individual molecules that are within a nanometre of each other (a nanometre is about ten thousand times smaller than the width of a human hair). The team used a technique called Atomic Force Microscopy (AFM) to measure this force. The flexible contact tips of the setules are triangular (pictures available see notes), and they have an amazingly high adhesive force on the underlying surface.
Andrew Martin, from the Institute of Technical Zoology and Bionics in Germany, said, "We found out that when all 600,000 tips are in contact with an underlying surface the spider can produce an adhesive force of 170 times its own weight. That's like Spiderman clinging to the flat surface of a window on a building by his fingertips and toes only, whilst rescuing 170 adults who are hanging on to his back!"