A gecko's tail is as crucial to the animal's acrobatic ability as its "sticky" feet, scientists report.
High-speed video reveals that the creature uses its tail as a "fifth leg" to prevent it from slipping as it climbs wet surfaces.
And the footage shows that if it does fall, a flick of the tail is all it takes for the gecko to land feet-down.
The study is published in the journal Proceedings of the National Academy of Sciences (PNAS).
The gecko is one of nature's best climbers - its feet are covered with millions of microscopic hairs that allow it to effortlessly cling to smooth surfaces.
But while the reptile's hairy toes have been extensively studied, little has been known until now about the role of the gecko's tail.
Bob Full, director of UC Berkeley's new Center for Interdisciplinary Bio-inspiration in Education and Research, and an author on the PNAS paper, said: "Initially, we thought the gecko's climbing ability was all in the feet, but now we know that this is clearly not true and the tail is critical."
Inspiring design
The scientists investigated the animal's acrobatic skills using high-speed video.
The researchers discovered that if a gecko was climbing up a slippery surface and lost its footing, the creature would press its tail to the wall to prevent itself from slipping backwards while it recovered its grip.
The team also found the animal's tail came into use during perilous falls.
Professor Full said: "We set up an experiment where we could see what would happen if a gecko fell off of the underside of a leaf.
"They started off with their backs to the ground, but when they start to fall, they swoosh around their tails, and by doing this they are able to rotate themselves so they move into a sky-diving or 'superman' pose."
This enabled the gecko to land on its feet, he told the BBC News website.
While other animals, such as cats, can rotate their bodies when falling to manoeuvre into a safer landing posture, the gecko is one of the few to use its tail to do this.
Machine mimic
Before landing, the creature's tail can come into use yet again.
Professor Full explained: "We put them in a vertical wind tunnel, and we found they could glide stably and use their tails to turn: they sweep it one way, they turn left; they sweep it the other way, they turn right."
In the wild, this kind of manoeuvring ability would allow the animal to direct its aerial descent to land on a perch rather than hitting the ground if it fell out of the rainforest canopy, he added.
The researchers believe the gecko's active tail could inspire engineers.
"This discovery is another example of how basic research leads to unexpected applications - new climbing and gliding robots, highly manoeuvrable unmanned aerial vehicles and even energy-efficient control in space vehicles," said Professor Full.
