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Geckos would definitely medal in a contest for nature’s best feet. The lizard’s sticky toes, covered in tiny hairs, mean it can climb across ceilings in a fantastic feat of evolution.
But scientists say the lizards’ tails are just as extraordinary, with geckos performing a remarkable, if ungainly, maneuver that allows them to land securely and at ballistic speeds on vertical surfaces like tree trunks.
“If an eagle were to land on a branch it would slow down with its wings so that the speed was almost zero and then it just touches down. It’s a graceful landing that requires a lot of control. The gecko does the exact opposite of that,” said Ardian Jusufi, a researcher at the Max Planck Institute for Intelligent Systems in Germany and the leader of the institute’s Locomotion in Biorobotic and Somatic Systems research group.
Initially, Jusufi and his team thought the geckos were able to steadily glide and then land in a relatively controlled way on tree trunks – with an earlier experiment showing they were able to use their tails to steer midair like skydivers when in a wind tunnel.
However, by capturing high-speed video of the Asian flat-tailed gecko and then building robot models of the lizards, to their surprise, the researchers found that the lizards crash headfirst at speeds of up to 21 kilometers per hour (13 miles per hour) and only stabilize on landing by using their tails to absorb the energy of impact.
“They approach the tree at very high speed and initially contact with front legs and the head and part of the torso. Then, the rear legs contact and now, because the forces are so great, the torso pitches back head over heels, and in the meantime, the tail is pressed down into the tree,” explained Jusufi, who is an author of a study on the findings that published in the journal Communications Biology on Thursday.
To better understand the forces the lizard experiences while making the maneuver, the team built two gecko-inspired robots – one with a tail and one without.
They 3D-printed the robots from soft plastic and rubber-like materials and catapulted them at a force plate, a sensitive scale that measures the landing impact. Only the robot with the tail could stick to the plate, validating the researchers’ observation that the tail was essential to stabilizing the lizard after it collides with a trunk at high speed.
Jusufi said the findings could help make more sophisticated robots. “This offers an alternative strategy for flying robots to land on walls, and flying robots can be used for construction or maintenance or search and rescue.”
He said it was possible that other species of lizards were able to perform such a maneuver, but it hadn’t been documented in any other animal before.
“It’s unexpected, right? In some ways it was thought if you have such amazing feet with such a high safety factor then why would you need a back-up mechanism?”
“It turns out that nature has some very challenging surfaces for these geckos. They slip on moss, bark, sand and such debris that they slip a lot even with the world’s best feet.”