March 18, 2008 -- Geckos are among the world's most talented acrobats, and now researchers know how these bright green lizards perform stuntman-type feats, such as climbing up slippery vertical surfaces, gliding and falling as if they're wearing a parachute.
The secret behind a gecko's gymnastics is literally at its behind; it's their tails.
Gecko tails allow for so many impressive moves that scientists are now contemplating outfitting future astronauts with robotic tails modeled on those of the chirping lizards.
"In emergency situations where thrusters or gyroscopic devices fail, a thin rod extending like a telescope with a sufficient ballast attached to its end could provide effective attitude control for any body in space," explained Ardian Jusufi, lead author of the study, which is published in this week's Proceedings of the National Academy of Sciences.
"An actuated robotic tail could be a more comfortable way for astronauts to control their body movements," added Jusufi, a University of California at Berkeley biologist.
For the study, he and colleagues Daniel Goldman, Shai Revzen and Robert Full put several geckos through obstacle courses designed to mimic the treacherous environments wild geckos must regularly navigate, like walking up slippery plant stems or traversing brittle tree bark from high levels.
Video footage of the elite lizard climbers revealed that under the best conditions, geckos grab onto surfaces with hairy toes that uncurl and peel within milliseconds. If they hit a slippery patch, their tails go into action.
"During rapid climbing, the tail functions like an emergency fifth leg," Jusufi told Discovery News. "If they slip with a front foot, the tail taps the wall and stops their heads from tipping backward. If this response is not enough, the geckos use their tail as a bicycle kickstand against the wall to stop them from falling head-over-heels."
While this natural navigational system prevents falls, the lizards do topple from time to time. The researchers prompted such falling by creating an impossible-to-traverse fake leaf. Even then, the gecko tail whipped into action.
Experiments videotaped in a wind tunnel showed that the gecko tail, which constitutes about 10 percent of the lizard's full body weight, whipped around clockwise to turn the lizard right side up. In slow motion, the movement looks like a graceful Olympic diver executing a mid-air twist.
Once the rotation is complete, the lizard spreads its legs and toes to parachute. Geckos will even sometimes glide, if necessary, using their tails to steer their bodies to desired landing spots.
Kellar Autumn, associate professor in the Department of Biology at Lewis & Clark College in Portland, Oreg. also studies geckos.
"This is just the coolest study," Autumn told Discovery News. "It took me by surprise, especially the findings about gecko gliding. That was a complete shocker."
He explained that most biologists previously thought the primary role of the gecko tail was to allow for fat storage.
"It took an interdisciplinary team to figure gecko tails out," Autumn said. "The study shows us how basic research can begin with relatively simple questions, such as how does a gecko avoid falling, before cascading into so many other significant findings with numerous application possibilities."
In addition to the astronaut tail idea, another application is already in the works. Full and colleagues are helping engineers create gecko-like robots. Stanford University researchers, for example, have constructed Spinybot and Stickybot.
Full said, "It is our goal to inspire the design of the most effective search-and-rescue robot ever built, one that can assist disaster rescue teams assisting in earthquakes, aid firefighters searching for trapped victims and sense chemical, biological and nuclear hazards before they cause harm."
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