Scientists find another use for lizards’ versatile tails: stabilization after headfirst crashes.
A gecko’s tail is a wondrous and versatile thing.
Gecko after landing on tree trunk. Credit: Photo by Ardian Jusufi
In more than 15 years of research on geckos, scientists at the University of California, Berkeley, and, more recently, the Max Planck Institute for Intelligent Systems in Stuttgart, Germany, have shown that geckos use their tails to maneuver in midair when gliding between trees, to right themselves when falling, to keep from falling off a tree when they lose their grip and even to propel themselves across the surface of a pond, as if walking on water.
Many of these techniques have been implemented in agile, gecko-like robots.
But Robert Full, UC Berkeley professor of integrative biology, and Ardian Jusufi, faculty member at the Max Planck Research School for Intelligent Systems and former UC Berkeley doctoral student, were blown away by a recent discovery: Geckos also use their tails to help recover when they take a header into a tree.
Those head-first crashes are probably not the geckos’ preferred landing, but Jusufi documented many such hard landings in 37 glides over several field seasons in a Singapore rainforest, using high-speed video cameras to record their trajectories and wince-inducing landings. He clocked their speed upon impact at about 6 meters per second, or 21 kilometers per hour — more than 200 feet per second, or about 120 gecko body lengths per second.
“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,” Jusufi said.
The videos show that when this gecko — the common Asian flat-tailed house gecko, Hemidactylus platyurus — collides head-on with a tree, it grabs the trunk with its clawed and padded toes so that, as its head and shoulders rebound, it has leverage to press its tail against the trunk to prevent itself from tumbling backward onto the ground and potentially ending up as someone’s dinner.
“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.”
This surprising behavior, and a demonstration that robots with tails that act similarly also can successfully recover from crash landings, will be reported this week in the Nature journal Communications Biology. Though this type of headfirst crash landing has not been documented previously among geckos or other gliding animals, the scientists suspect that other small, lightweight leapers — in particular, other lizards — use this as a backup when a perfect jump is impossible.
The Asian flat-tailed gecko would prefer a four-point landing after leaping to a tree trunk, but if it can’t slow down sufficiently, it may have to crash head first into the trunk, rebounding but stabilizing itself with its tail. Researchers at the Max Planck Institute for Intelligent Systems in Germany built a soft robot with an active tail to replicate this behavior. Credit:
Photos by Ardian Jusufi, illustration by Andre Wee
“They may have longer glides that are more equilibrium glides, and they land differently, but, for example, if they are trying to escape, they choose to do this kind of behavior, in part because size matters,” Full said, noting that the lizards measure only a couple of inches from snout to tail tip. “When you’re that small, you have options that aren’t solutions for big things. So, this is sort of a body-mediated solution that you don’t have if you’re bigger.”