The snake dangles 49 feet (15 meters) off the ground, tail entwined around a branch. Suddenly, the animal rears up and launches, flinging its body toward the forest floor.
In other reptiles, the leap would be suicidal, or at least an invitation for broken bones. But the snake in question is a Chrysopelea paradisi, one of five related species of tree-dwelling snakes from Southeast and South Asia. When these snakes leap, it's not to nosedive; it's to glide from tree to tree, a feat they can accomplish at distances of at least 79 feet (24 m).
What no one knows is exactly how these reptiles manage to fly so far without wings. Now, a new study finds that the snakes' amazing aerial abilities may all be in the way they move.
"For any flier, you really need to know the basics: How fast is it going, what's the shape of the flier, what is the shape of the wing," study author Jake Socha, a biologist at Virginia Tech, told LiveScience. "With this new study, we now really get insight into what the exact position of the body is as it's in this really developed glide."
Socha presented his research today (Nov. 22) at the American Physical Society Division of Fluid Dynamics meeting in Long Beach, Calif. The study will be published this week in the journal Bioinspiration and Biomimetics.
Socha has been researching the aerodynamics of gliding snakes for years. His previous studies have found that these snakes flatten themselves as they launch, undulating side-to-side as if they're slithering in mid-air. They glide fast, between 26 and 33 feet per second (8 to 10 meters per second), Socha said.
To find out more about how the snakes position themselves during the glide, Socha and his colleagues videotaped snakes launching themselves from the 49-foot tower toward the ground. The researchers put white dots on the snakes' bodies so they could calculate where the animal was in space at each point during the flight. The technology is similar to that used to do motion capture for video games or animated movies, Socha said.
The snakes are more than happy to glide for the cameras, Socha said.
"They glide; that's what they do," he said. "So they're like, 'I'm outta here, I'm gonna go down there.'"
Next, the researchers used the video to model and analyze the forces acting on the snakes' bodies. They found that the snakes aren't horizontal during their glide; they're actually tilted up about 25 degrees relative to the airflow created by their flight. They hold the front half of their bodies fairly still, with the exception of the side-to-side undulations. Meanwhile, their tails move up and down. Video of snake flights is available at Socha's website.
"We definitely find that there are good places to be and bad places to be, places that augment your force production and places that make it less favorable," Socha said. "It seems that the snake is using a configuration that is highly favorable to being a good glider."
Surprisingly, although the snakes move down toward the ground, the net force on their bodies during the glide is an upward force — at least briefly. That means that if you add up every force acting on the snake, Socha said, you'd be left with a small force pushing the snake skyward.
The snake doesn't actually start moving up in part because they don't fly far enough for the net upward force to have an effect, and in part because the upward force disappears quickly, Socha said.
Serpents in flight
Transient or not, the fact that the snake isn't gliding in equilibrium is exciting, said Greg Byrnes, a postdoctoral researcher at the University of Cincinnati who studies gliding mammals.
"You have something that doesn't look like it should be able to fly at all, and it actually is able to fly well enough that it supports more than its body weight with force," Byrnes, who was not involved in the research, told LiveScience. "That's a pretty cool thing."
"For a long, long time, people have thought it's a very simple process, basically like flying a paper airplane," Byrnes added. "It turns out that's not true."
The next step, Socha said, is to work out how the snakes' body position affects its glide.
"The whole snake itself is just one long wing," Socha said. "That wing is constantly reconfiguring, it's constantly reforming and contorting… Parts of the body, depending on where they are in space, might be interacting with the wake from the front part of the body, and this might hurt or help or be neutral."
The findings could eventually be applicable to building small, agile flying vehicles, Socha said. But, he said, they're also exciting in their own right.
"Why is it that you don't tumble out of the sky if you're a snake?" he said. "Now we have the framework for doing detailed studies of the aerodynamics."