The unique grip of geckos' toes that lets them effortlessly scale walls and hang upside down is activated by the feel of gravity tugging on their bodies, not the kind of surface they're scampering along, according to new research.
University of Calgary professor Anthony Russell stuck the animals in a kind of boxed-in gecko runway to watch how they moved along different surfaces.
Put on a slick surface of Plexiglas, the creatures slipped and slid their way along when the course was completely flat.
When it was raised to a 10-degree angle, about half of those geckos tested engaged microscopic hair-like branches that extend from their toes, creating an interaction with the surface that let them get a tighter grip.
By the time the runway was tilted to 30 degrees, all the geckos were running with their grips on go.
The angle at which the grips started working was the same whether the geckos were scooting along a smooth surface or an easily navigated sandpaper base, showing that it's the angle that makes them engage rather than the type of surface, Prof. Russell said.
"They are preprogrammed to use it," he said. "So it's one of these systems where the animal is registering its body orientation and that is telling it, okay, there's a more difficult set of circumstances here, employ your insurance policy."
The signals are delivered to the geckos by their central nervous system, the thing that enables all creatures to feel whether they're accelerating or decelerating and which way is down, said Prof. Russell.
It doesn't make sense to have the grips working all the time since when they're engaged they create friction that slows the animals down, he said.
These grippy toes work well for geckos in the wild, since they can dart up and down rocks in the deserts where many of them live, ducking inside crevices in an instant to evade predators. They're also useful among trees - geckos can scamper across leaf surfaces, too slippery for most predators, to indulge in a virtual buffet of insect prey.
Understanding how the geckos' grip works is also important to a number of areas of research, said Prof. Russell.
For all their grippiness, geckos aren't actually sticky, said Prof. Russell. Their hold is caused by an interaction between the polarity of the little hairlike branches and whatever surface they happen to be holding on to, with the toes adapting as the surfaces change.
Research into how that works can lead to an adhesive that sticks again and again without leaving behind marks or chemical traces, he said.
It also has implications for military use. Gecko-style grips could be added to robots to help them scale walls and pick among rubble while looking for unexploded bombs or heading deep into unknown territory.
"So something like a little gecko-based climber could actually go up those surfaces and continue on carrying a little camera with it and exploring places that we can't otherwise get to."
Prof. Russell's research will be published in Wednesday's online edition of the biological research journal of the UK's national Academy of Science.