Watch this gecko smash headfirst into a tree—and still stick the landing | Science

PHOENIX—Imagine slamming your head into a wall at a Lamborghini’s top speed, and you’ve got a good sense of what it’s like for a gecko to smack headfirst into a tree as it hurtles from branch to trunk. “The landing looks quite brutal,” says Lara Ferry, an integrative biologist who studies animal morphology at Arizona State University, West Campus.

Yet the small lizards with the famously sticky feet usually walk away unharmed. High-speed video presented here last week at the annual meeting of the Society of Integrative and Comparative Biology reveals how geckos’ bodies dampen the impact, helping them land safely and hold fast to their perches. But lizards aren’t the only ones with a jump trick: Another team described how tiny invertebrates called springtails use water droplets to cushion their landings as they make their own high-velocity leaps.

Both projects are uncovering new insights into how animals contort their bodies to control their landings, says Jake Socha, a comparative biomechanist at the Virginia Polytechnic Institute and State University who was not involved with either study. The work, he says, could help engineers design robots that are similarly capable of walking away from high-impact crashes.

Many tree-dwelling creatures, like gliding squirrels and woodpeckers, can stick their landings with ease, thanks to skin folds and feathers that slow them down to gently land feet first. But most lizards don’t have anything like that, says Ferry, who was not involved in either study. So how do they survive their brutal landings?

Interdisciplinary biomechanist Ardian Jusufi decided to find out. While in a rainforest in Singapore for fieldwork, the Max Planck Institute for Intelligent Systems scientist filmed and analyzed 37 landings of Asian flat-tailed geckos (Hemidactylus platyurus).

When the lizard crashes into its desired tree, its head bounces back on impact (see video, above). The upper half of its body then pitches backward, sliding off the trunk like a banana peel. But the back feet and tail are still able to hang on, anchoring the lizard until the rest of its body swings back up and it settles with all four feet planted, Jusufi and colleagues reported at the meeting. “They ‘roll’ into it,” he said.

The researchers suspected the gecko’s tail was key to its success. So they built a flexible robot with an adjustable tail and catapulted it—with and without the tail—toward a vertical wall (see video, below). The scientists recorded the landings and measured the forces involved. Shortening the tail by 25% required twice as much adhesive force in the feet to keep the lizard from falling, the team reported this month at the meeting and in September 2021 in Communication Biology. With no tail, the robotic gecko fell off almost every time. “That tail is a critical part of the animal’s response in being able to keep a grip,” Socha says.

John Hutchinson, an evolutionary biomechanist at the Royal Veterinary College who was not involved with the work, thinks other lizards may do likewise. “Their body form is fairly ‘bog standard’ for lizards,” he says, “so it may be that a wide variety of ‘boring’ lizards use these exciting landing behaviors when they must.”

Springtails use other exciting maneuvers to land. These moisture-loving arthropods are about half the size of a sesame seed and jump up to 25 times their body length when disturbed. (For a human such a leap would cover the distance of two tennis courts.) They take off in 2 milliseconds—50 times faster than the blink of an eye—from wet dirt, leaf litter, even the surface of puddles by the thousands, “like minipopcorn popping” says Saad Bhamla, a biophysicist at the Georgia Institute of Technology (Georgia Tech).

Bhamla and Victor Ortega-Jimenez, also a Georgia Tech biophysicist, filmed and analyzed what happens when springtails land (see video, below). Like geckos, these creatures also dampen their impact—but with a water droplet instead of a tail, Ortega-Jimenez reported at the meeting.

Victor M. Ortega-Jimenez/Bhamla Lab

The underside of the springtail has a long tube called a collophore that grabs a drop of water as the springtail takes off. The added weight of the droplet helps stabilize the flying animal. Thus, the droplet hits first, acting like a cushion. In addition, the springtail makes sure it lands feet—and water droplet—first by flexing its twirling body into a U shape midair, Ortega-Jimenez reported.

“Both geckos and springtails are deforming their bodies and using a specialized structure—the tail in geckos, the collophore in springtails—to facilitate a perfect landing,” Ortega-Jimenez explains.

But size matters. Given the forces involved, what works for small organisms won’t work for us, Hutchinson says. “Humans would go splat if they tried.”