A Tokay gecko climbs while inverted on glass in this 2000 photo. Photo: Lewis & Clark College/AP

Calling it an ancient mystery that has baffled mankind since the time of Aristotle, a team of U.S. biologists and engineers say that they have finally explained the gecko's incredible climbing ability.

Geckos — a small lizard with a soft skin, a stout body and a large head — are often kept as pets by children. In spite of their weak limbs, they can dangle their entire weight from a wall by a single toe, and they can heave themselves up a sheet of polished glass at remarkable speed, covering one metre in only a second.

The research team's work, published Monday in the Proceedings of the National Academy of Sciences, explains that geckos are able to scale even sheer walls because the hairs on their feet form electrodynamic bonds with the surface, a force discovered possible by Johannes van der Waals more than a century ago.

Gecko feet are covered with millions of tiny setae, hairs only twice as long as a strand of human hair is wide. Each seta has 1,000 tiny pads on its tip, a tip that is so small it is below the wavelength of visible light, only 200 billionths of a metre wide.

Studying the Tokay gecko, a native of Southeast Asia and one of about 800 species of the lizard, the team believed that it was the size and shape of the foot hairs that determined a gecko's ability to adhere to a surface, not what the hairs were made of. They then used that knowledge to create synthetic foot-hairs from two different substances.

"Both ... stuck as predicted," says lead researcher Kellar Autumn, assistant biology professor at Oregon's Lewis & Clark College. "Our results provide the first direct experimental verification that ... van der Waals force is definitely what makes geckos stick."

"Intermolecular forces come into play because the gecko foot hairs split and allow a billion spatulae to increase surface density and come into close contact with the surface."

Mr. Autumn says that scientists and inventors looking to create a super-glue will not have to replicate precisely the incredibly intricate design of geckos' feet.

"We can apply the underlying [principle] and create a similar adhesive by breaking a surface into small bumps," he said, adding: "the artificial foot-hair tip model opens the door to manufacturing dry, self-cleaning adhesive that works under water and in a vacuum."

The project has even raised the interest of the U.S. military. The Defense Advanced Research Projects Agency, the central research and development organization for the Pentagon, has supported the research, though it has not revealed any plans it might have for it.