How geckos stick to walls without any effort

A new study has revealed that death has no impact on strength geckos use to adhere to surfaces.

Biologists at the University of California, Riverside, found that geckos don't require effort in being sticky and death affects neither the motion nor the posture of clinging gecko feet and they have found no difference in the adhesive force or the motion of clinging digits between our before- and after-death experiments.

Timothy E. Higham, an assistant professor of biology, said that that there have been suggestions in the literature for many years that gecko adhesion at the organismal, or whole-animal, level (where the intact animal initiates adhesion) requires an active component such as muscle activity to push the foot and toes onto the surface in order to enhance adhesion.

The researchers used a novel device involving a controlled pulling system. This device applies repeatable and steady-increasing pulling forces to the gecko foot in shear. Specifically, the device measures clings by pulling a gecko foot in a highly controlled manner along a vertical acrylic sheet while simultaneously recording shear adhesion with video cameras.

The experiments showed that the adhesive force or motion of a gecko foot when pulled along a vertical surface was similarly high and variable when the gecko was alive and immediately - within 30 minutes - after death.

The controlled experiments the researchers performed are the first to show that dead animals maintain the ability to adhere with the same force as living animals. The results refute the notion that actions by a living gecko, such as muscle recruitment or neural activity, are required for gecko feet to generate forces.

The new work suggests that the "active" component of gecko adhesion is actually a reduction of adhesion force when the gecko "hyperextends" its digits - that is, lifts them off the ground by curling up only the tips of the digits while the rest of the foot remains on the surface.

The study was published online in Biology Letters.