As they wiggle and undulate, the snakes are transforming their bodies for flight.
David Waldstein – Trilobites – 1 July 2020
“Jake Socha is an expert on flying snakes who uses detailed scientific terminology such as “this big, wiggly, ribbon thing” to describe his soaring quarry.
It is an apt description, but don’t be fooled. When a snake launches off a tree in its Southeast Asian habitat and lands on another tree dozens of feet away, there is nothing random about those wiggles.
A professor of biomedical engineering and mechanics at Virginia Tech, Dr. Socha and his colleagues published a study on Monday in Nature Physics supporting the hypothesis that the midair undulations (the wiggles) are actually carefully coordinated and highly functional processes that enhance the dynamic stability of the snake in flight.
“I wouldn’t say all the mysteries are solved,” Dr. Socha said, “but we have a big piece of the story filled in.”
Flying is a bit of a misnomer for what the snakes do. The slithering airborne creatures tend to fall strategically or glide, meaning they do not gain altitude like a bird or an insect. Their flights generally last only a couple of seconds, at a speed of around 25 miles per hour, and they land without injury. To the untrained eye, it might look as if the snake just fell out of a tree by accident, wiggling frantically as it plummets to earth. Not so.
Once it goes airborne — after inching out on a tree limb and pushing off the branch — the snake moves its ribs and muscles to extend the width of its underside, transforming its body into a structure that redirects airflow like a parachute or a wing. A cross section of the snake’s body midair would show that its normal circular shape becomes triangular and the whole body undulates as it glides toward its target.
Once in Singapore, Dr. Socha and a group of researchers witnessed a snake jump from 30 feet up and travel over 60 feet in the air on a windless day.
“It was like an athlete hitting its stride,” he said. “It was like, ‘I know what I’m doing, I’m off and you’ll never see me again.’”
For years Dr. Socha wondered if the undulations were functional for flight or whether the snakes were simply repeating the same motion in air that they use to move across land and through water.
The researchers, including Isaac Yeaton, a doctoral candidate in mechanical engineering, took about a half-dozen flying snakes to a four-story, black-box cube on the Virginia Tech campus. The cube, which can be used for student projects and experiments in arts, science and engineering, is equipped with a high-speed, motion-capture camera system. The researchers attached infrared reflective tape to the snakes, and fashioned a high tower with a launching branch and a lower tower disguised as a tree for a landing spot. Then they let the snakes fly.
Mr. Yeaton, who was once surprised when one of the snakes landed in his arms as he stood on the floor, said they observed over 150 flights of Chrysopelea paradisi — one of five kinds of flying snakes — during a week in 2015.
“It’s hard to believe a snake can do this,” Mr. Yeaton said. “It’s kind of scary. But there’s a lot of intricate things that are going on.”
The researchers collected the data and then created three-dimensional computer models to show every angle of the snake in flight.
The models illustrated that the undulations contain vertical waves as well as horizontal. And the waves flow proportionally, with the vertical waves twice the frequency of the horizontal waves.
They also found that the back end of the snake moved up and down vertically along what they called the dorsoventral axis, adding to its up-and-down or pitch stability.
“Other animals undulate for propulsion,” Mr. Yeaton said. “We show that flying snakes undulate for stability.”
Using the computer models, the researchers could also eliminate some or all of the undulations for comparison. Without them, the snake falls haphazardly and dangerously, like a Frisbee that is thrown without spin.
The information from the study, the researchers said, could have applications for robotics, particularly in search and rescue. Because, as Dr. Socha might say, wiggly ribbon things are good at getting into tight spaces, like through the rubble of an earthquake. And they could fly from one rescue site to another.
“I hope that before the end of my life that we do have a search-and-rescue robot based on flying snakes,” he said.