For Geckos, Going Downhill Requires a Reverse Effort

For geckos, climbing along walls and even upside down is a piece of cake, but going downhill, on the other hand, requires some effort, according to new research.

Geckos rely on "setae," millions of very fine hair-like structures on the underside of their toes, for their Spiderman-like skills. While this feature provides for some sticky feet, it can actually hinder geckos when on a downhill slope.

This adhesive system provides increased surface area and close contact between the gecko's foot and the surface on which it rests. However, this weight distribution works best along the natural curvature of the setae. Wouldn't the gecko then slip going downhill since it's going in the opposite direction?

Biologists at the University of California, Riverside have now conducted experiments on geckos in the lab to find the answer. They found that when moving on steep downhill surfaces geckos reverse the position of their hind feet so that their adhesive system works as a sort of brake. This way, the setae are aligned along their natural curvature to oppose gravity. Specifically, on a 45-degree downhill slope, the geckos were found to rotate their hind limbs backward up to 70 degrees more, towards their tails.

"This multi-functionality of the gecko adhesive system permits effective locomotion on both uphill and downhill slopes," Timothy Higham, an assistant professor of biology, in whose lab the research was conducted, said in a statement. "Without this ability, geckos would be effective at going up, but they would not be able to descend as easily. Indeed, they could plummet downhill."

Most people might associate geckos' feet with Velcro and suction cups, but "gecko adhesion is directional," explained Aleksandra V. Birn-Jeffery, the first author of the research paper. The intermolecular forces and friction that allow these lizards to stick to almost any smooth surface act along the long axis of their toes, so the foot has to be positioned a certain way when they walk.

"It is curious that not many people have looked into how geckos move downhill," Higham added. "We are the first to really figure this out."

The results were published in the journal Biology Letters.