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Slithering on Air: Flying snakes glide through the treetops

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1:27pm, August 7, 2002
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Tree-climbing animals that can fly or glide are more likely than others to survive a fall. Though only birds, insects, and bats can truly fly, many animals, such as flying squirrels and flying lizards, have evolved wing-like flaps of skin for floating–at least briefly–on air.

Snakes generally aren't well suited for flight. So, scientists had assumed that snakes that move through air are merely parachuting from tall trees. However, a new study demonstrates that at least one species of flying snake does glide, and it does so nearly as well as other gliding animals.

The paradise tree snake (Chrysopelea paradisi) of Southeast Asia slithers while in the air, creating fleeting S-shape wings, says a report in the Aug. 8 Nature. The snake also flattens itself to twice its normal width, probably aiding lift.

"These animals are much more sophisticated than we thought," says the report's author, John J. Socha of the University of Chicago. "Not only can they move horizontally and significantly, they also have the ability to change direction." One talented snake even avoided a tree in midair, he reports.

In the experiment, Socha observed each snake hang in a J-shape position on a branch atop a 10-meter tower. It then flung itself from the branch, generating forward speed.

Socha videotaped the leaping snakes from two angles. Using reference dots painted on the snakes, Socha traced their in-flight movements and overall trajectories. Once in air, each snake flattened out and moved side-to-side. It steered with its head to make sudden midflight turns

The snakes traveled farther horizontally than they would have if they were simply falling, so they are true gliders, Socha says. Though they typically landed about 10 meters from the tower base, one Carl Lewis of the snake world consistently glided farther than its peers, up to 21 meters. After each landing, volunteers sprinted to recapture the scientifically valuable snake before it could slither away.

Gliding probably both prevents death in case of a fall and helps C. paradisi move quickly from treetop to treetop as it chases prey and flees predators, speculates Socha.

A snake's cylindrical shape is "all wrong" for an airfoil, notes biologist Steven Vogel of Duke University in Durham, N.C. So, it's exciting that these snakes have evolved such clever strategies for flight, he says.

"The snakes are also surprisingly maneuverable," Vogel adds. "Halfway down the glide, they can decide where they're going to land."

Neither Socha nor Vogel knows of any other flying system that uses side-to-side motion to generate lift. Throughout history, people have tried to copy animals to make flying machines, Vogel says, but this design may not be the best one to try. "Parachutes are much, much safer," he quips.

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