The Gecko in the Flight Simulator
It’s a lizard! It’s a plane! It’s Supergecko! Researchers at UC Berkeley (where else) put a gecko into a wind tunnel to watch it fly. News about gecko’s magic feet that allow it to run vertically up glass is almost old hat now (08/27/2002, 01/04/2005). Even a gecko can lose its footing, though, and thereon hangs a tail.
Publishing in PNAS,1 (the cover story of the March 18 issue), the team had some superlatives to share about these critters that skitter:
In a single second of vertical running, geckos travel 15 body lengths and take 30 steps. During rapid climbing, their toes attach in 5 ms [milliseconds, or thousandths of a second] and detach in only 15 ms…. During our initial explorations of climbing on realistic surfaces and upsidedown locomotion, we noticed that a gecko’s agility involved far more than just secure footholds. Here, we pursue our observations by testing the hypothesis that the gecko’s tail enhances its scansorial and arboreal performance.
The speed translates into 3 feet per second. Taking advantage of atomic van der Waals forces (01/30/2008), they attach and detach their feet 30 times per second while running straight up. Amazing as the feet are (12/06/2006), the tail is the key to this tale.
The active tails of the gecko function as stabilizers and gliders. When the gecko finds itself in a rapid free-fall, unlike Wiley E. Coyote, it can flip right over. The tail twists and puts him right-side-up in mere milliseconds. Then, the tail provides pitch control as the gecko assumes Superman position, allowing him to land on all fours almost every time. Unlike cats, which can right themselves during a drop by twisting the spine, geckos keep their spine rigid. They flip upright by doing the twist with their active tails.
Why the flight simulator? The wind tunnel experiments showed that the broad area of the tail helps slow and control the descent, like a glider. During the glide, they control pitch and yaw and can actually steer themselves a bit toward safety.
In addition, the tail acts as a stabilizer when climbing on a vertical surface. The tail adds pressure and balance if the gecko finds itself leaning backward – even as much as 60 degrees. If a foot falters on a slippery patch, the gecko shifts its tail to the side like a bicycle kickstand. The tail, then, serves both as a fifth leg and a glider. The authors did not say whether a gecko can grab a branch with its tail on the way down.
Science Daily, Live Science, the BBC News and PhysOrg summarized the paper with a picture of a gecko in free-fall. (The researchers, incidentally, abided by all the rules of the U.S. Animal Welfare Act.) After watching these tricks, the light bulb went on: “The discovery is already helping engineers design better climbing robots and may aid in the design of unmanned gliding vehicles or spacecraft,” the press release said. “Perhaps, the researchers say, an ‘active’ tail could help astronauts maneuver in space.”
1. Jusufi, Goldman, Revzen and Full, “Active tails enhance arboreal acrobatics in geckos,” Proceedings of the National Academy of Sciences USA, published online on March 17, 2008, 10.1073/pnas.0711944105.
The article did not mention evolution. The paper was listed under the category Evolution, but has design written all over it.