Defying Gravity

Article excerpt

Hairs on the leg tip of a spider, magnified seventy diameters

The next time you see an ant or a spider walking upside down, consider this: rope systems designed to hold rock climbers can support at least ten times the weight of an average adult, but the critter clinging to your ceiling has vastly more protection than that. Now Antonia B. Kesel, a zoologist at the University of Applied Sciences in Bremen, Germany, and her colleagues have applied a technique called atomic force microscopy to precisely measure the adhesive forces involved.

To hold on, insects, including ants, rely on small claws or on sticky foot secretions. Spiders, however, have a different adhesive structure at the tip of each leg, formed from a dense aggregation of miniature hairs called setae. Each seta is covered with even smaller hairs whose tips are shaped like sails. The "sails" can conform to every bump and cranny of a surface, acting as intimate contact elements between the wall and the foot. …