Midway News--Medicine on the Midway, Fall 2002

2 M E D I C I N E O N T H E M I D W A Y Tracking flying snakes Ophidiophobia, the fear of snakes, traditionally has been among the most common phobias — and that was back when all we knew snakes could do was slither, burrow, swim and climb. Just imagine if snakes could fly. In fact, some 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 of these airborne creatures. In an August issue of Nature, the sixth-year graduate student described some of the aerodynamics of the Chrysopelea paradisi, or paradise tree snake — one of five snake species that are purported to “fly.” 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, turns like most other flyers. Instead, the paradise tree snake turns as it undulates from side to side. The Nature article, titled “Gliding flight in snakes,” also describes the threedimensional 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 threedimensional 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 the 33-foot platform, the snakes could glide as far as 70 feet, make turns up to 90 degrees and always seemed to land without injury. The Nature article stems from a larger research project Socha conducted as part of his dissertation, which he defended this past 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 undulates 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 film and videotape, and more than a hundred 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 back as far as Herodotus, a Greek historian in the fifth century B.C. Most flying snakes grow three to four 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