As the Asian flat-tailed house gecko glides across the rainforest from one tree to the next, it makes far from a gymnast’s perfect landing.
The gecko crashes head-first into the tree as it grips with its front legs to hold on. But the gecko loses its grip, swinging back head over heels, holding on only with its back feet and its tail.
The tail is what keeps the gecko from smacking into the tree or from falling off, new research finds.
Scientists at the University of California, Berkeley, have been studying geckos for more than 15 years and have found all the ways they use their tails. Tails help them maneuver in midair when they are gliding between trees and help them propel themselves across a pond’s surface, as if they are walking on water.
But the researchers also observed as the geckos were able to avoid crash-landing into trees and avoid falling off—all by using their tails.
For their recent study, scientists observed 37 Asian flat-tailed house geckos (Hemidactylus platyurus) in a Singapore rainforest. They used high-speed cameras to record their leaps and not-so-graceful landings.
“Observing the geckos from elevation in the rainforest canopy was eye-opening. Before take-off, they would move their head up-and-down, and side-to-side to view the landing target prior to jumping off, as if to estimate the travel distance,” study author Ardian Jusufi, faculty member at the Max Planck Research School for Intelligent Systems and former UC Berkeley doctoral student, said in a statement.
Geckos probably would prefer a less awkward touchdown, but Jusufi observed many of these hard landings in his research. He recorded their landing speed at more than 6 meters per second (about 20 feet). Because the geckos measure only a couple of inches, that’s equal to about 120 gecko body lengths.
The videos showed that when the gecko hits a tree, it holds on to the surface with its clawed toes. As its head and shoulders are flung back, it uses its tail to press against the trunk of the tree to stop from falling backward onto the ground.
“Far from stalling, some of these lizards are still accelerating upon impact,” Jusufi said. “They crash headfirst, pitch back head over heels at an extreme angle from the vertical—they look like a bookstand sticking away from the tree—anchored only by their rear legs and tail as they dissipate the impact energy. With the fall-arresting reflex happening so fast, only slow motion video could reveal the underlying mechanism.”
The researchers mathematically modeled their findings and then reproduced them in a soft robot with a tail. The results were published in the journal Communications Biology.
They note that a structure similar to a gecko’s tail could help stabilize flying robots like drones when they make vertical landings.
An Evolution of Uses
This original use for the gecko’s tail is an example of an exaptation: when a trait or structure of an organism takes on a new function other than its original purpose.
“Until recently tails had not received as much attention as legs or wings, but people are now realizing that we should think of these animals as five-legged, in a way—pentapedal,” Jusufi said.
Lizard tails, like those of the geckos in these studies, are quite interesting, herpetologist Whit Gibbons, professor emeritus of ecology at the University of Georgia, tells Treehugger.
“Tails are used for myriad purposes among animals, and lizards have cornered the market on sacrificing their tail to a predator in order to escape,” says Gibbons, who wasn’t involved in this study.
“Other uses of tails among geckos or other lizards are for energy storage, balance when running, or use as a rudder when swimming. One of the geckos even curls its tail to mimic a venomous scorpion. Geckos are amazing in their versatility in means of survival, and identifying another use of the tail adds to their intrigue.”
Gibbons says that he’s never surprised when researchers uncover a novel behavior in reptiles or other animals and see the importance of these particular findings.
“Finding out that some geckos use their tail in balancing after a perilous flight and crash landing is important in further revealing how fascinating animals can be and adding to reasons for appreciating other species,” Gibbons says.
“The particular behavior also has potential for use in robotics and aerodynamics through demonstrating the functionality of a balance mechanism in a real-life situation.”
