An article in this week’s New York Times Science Observer column highlights the paradise tree snake (Chrysopelea paradisi) of Asia, long known to escape predators by hurling itself from a tree and sailing through the canopy to alight on a new tree. Studies suggest it can travel as far as 300 feet in this way. A new study published in the oddly-titled and hard-to-find journal Bioinspiration and Biomimetics analyzes the mechanics of this “flight”:
. . . a study in which scientists threw the snakes from a 50-foot tower and recorded their descent on video suggests that the snakes are active fliers, manipulating their bodies to aerodynamic effect.
“It essentially looks like they are slithering in the air, like a whip moving left and right,” said Jake Socha, the study’s lead author and a biomechanist at Virginia Tech. “The body itself moves up and down as well.”
Dr. Socha and his colleagues found that the paradise tree snake tilts its body about 25 to 30 degrees relative to the airflow to stay as aerodynamic as possible. The farthest a snake was able to travel from the tower was about 79 feet.
This is far better seen than described; here’s a nice video from PBS:
And Wikipedia says a bit more:
Upon reaching the end of a tree’s branch, the snake continues moving until its tail dangles from the branch’s end. It then makes a J-shape bend, leans forward to select the level of inclination it wishes to travel to control its flight path, as well as selecting a desired landing area. Once it decides on a destination, it propels itself by thrusting its body up and away from the tree, sucking in its stomach, flaring out its ribs to turn its body in a “pseudo concave wing” all the while making a continual serpentine motion of lateral undulation parallel to the ground to stabilise its direction in midair in order to land safely.
The combination of sucking in its stomach and making a motion of lateral undulation in the air makes it possible for the snake to glide in the air, where it also manages to save energy compared to travel on the ground and dodge terrestrial bounded predators. The concave wing that a snake creates in sucking its stomach, flattens its body to up to twice its width from back of the head to the anal vent, which is close to the end of the snake’s tail, causes the cross section of the snake’s body to resemble the cross section of a frisbee or flying disc. When a flying disc spins in the air, the designed cross sectional concavity causes increased air pressure under the centre of the disc, causing lift for the disc to fly. A snake continuously moves in lateral undulation to create the same effect of increased air pressure underneath its arched body to glide. Flying snakes are able to glide better than flying squirrels and other gliding animals, despite the lack of limbs, wings, or any other wing-like projections, gliding through the forest and jungle it inhabits with the distance being as great as 100 m. Their destination is mostly predicted by ballistics; however, they can exercise some in-flight attitude control by “slithering” in the air.