U of C researcher tracks path of flying snake


August 7, 2002

The sight of a snake strikes fear in the hearts of millions of people. Fear of snakes, or ophidiophobia, is among the most common phobias. Snakes can crawl, burrow, swim and climb. Can you imagine if these slithering reptiles could fly?

Some actually can. More precisely, they glide or parachute in the same fashion as a flying squirrel, frog, lizard or fish.

University of Chicago biologist Jake Socha has been studying the gliding patterns and biomechanics o f these airborne creatures. In the Aug. 8 issue of Nature, the sixth-year graduate student describes some of the aerodynamics of the Chrysopelea paradisi, or paradise tree snake--one of five snake species that are purported to "fly".

Snake flying through air

A flying snake (Chrysopelea paradisi, or paradise tree snake) in the air just after takeoff, beginning to form the wide-amplitude "S" posture it takes when undulating. The snake has flattened its body from head to vent, forming a slightly concave lower surface. The bulge in the body near the head is the heart, which does not flatten. The snake is 71 centimeters long from the snout to vent and has a mass of 41 grams. © Jake Socha, National Geographic Society

Socha found that the aerial behavior of this snake is unlike any other glider. It exerts remarkable control over the direction it takes, despite an apparent lack of control surfaces. For example, while in flight, the snake does not bank, or lean into, the turns like most other flyers.

"Most flyers use some kind of a banking technique," he said. Instead, the paradise tree snake turns as it undulates from side to side.

The Nature article, titled "Gliding flight in snakes," also describes the three-dimensional kinematics of gliding by the paradise tree snake. More specifically, the snake changes its undulation pattern while airborne: the amplitude, or height of the waves, is two to three times larger, and the frequency is one-third lower.

For the study, Socha videotaped and photographed various snakes taking off from a 33-foot-high tower in an open field at the Singapore Zoological Gardens. He positioned two video cameras to record in stereo, enabling the three-dimensional reconstruction of the head, midpoint and vent coordinates of the snake throughout its trajectory.

Socha found that C. paradisi prepares to take off by hanging from a branch looping its anterior body into the shape of a "J". The snake then jumps by accelerating up and away from the branch. Using its ribs to change its body shape, it flattens from head to vent. (Snakes also flatten when threatened, to absorb more sunlight or when posturing, like a cobra does prior to attack.)

"But while in flight, it not only flattens its entire body, it moves at the same time," Socha said. "It's actually undulating in the air. So whatever muscles it's using to flatten are probably decoupled from the muscles it's using to undulate."

Socha also found that its orientation changes throughout the trajectory. Before beginning to undulate, the snake pitches its body downward, and then brings its head and vent together toward the midpoint to form an "S" shape.

The snake has some degree of control, undulating through the air as if swimming, moving the tail up and down and side to side. From a 33-foot-height, they can glide as much as 70 feet across, make turns up to 90 degrees and always seem to land without injury.

The Nature article is part of a larger research project Socha has been conducting as part of his dissertation, which he plans to defend in November. His research also includes detailed analyses of takeoff and how body size relates to gliding ability.

But the young biologist had to start from zero.

"I didn't know where to begin," Socha admitted, since little was known about these snakes in general. He couldn't use computer or physical models since the shape of the snake, its posture and how fast it undulated were unknown.

Instead, with the support of the National Geographic Committee for Research and Exploration, Socha traveled to Singapore twice and Thailand once to study the snakes. After six years of research, miles of videotape and film, and more than his share of snake bites, Socha has emerged as rare as his subject: a flying snake expert.

Scientists have documented the existence of these animals for only a century, but legends of "winged snakes" go as far back as Herodotus, a Greek historian in the fifth century BC. Most flying snakes grow 3 to 4 feet long and live in the trees in the lowland tropical rainforests of South and Southeast Asia.

Their temperament varies from species to species, and from individual to individual, but all five species of flying snakes are in the Colubridae family, and officially are classified as harmless (although, according to Socha, some species will bite if they get the chance). Flying snakes secrete mild venom that is only dangerous to their small prey.

They are diurnal and opistoglyphous, or rear-fanged. These back teeth measure only 2 to 3 mm long and each have a small groove that runs along the fang's outer edge, where the venom drips down and into the prey.

Much is still not known about flying snakes, such as their predators, their sleep habits or how often they glide. There have been no studies that document their movement through the trees, but in general, animals that glide do so to travel more efficiently, to chase prey or to escape a predator.

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