If the idea of flying snakes was frightening enough to produce a legendary film, how much worse is it to learn such creatures of nightmares are real. Technically snakes do not fly (unless they stow away on planes) but some are capable of falling with style, gliding remarkable distances, and scientists have now revealed how they do it.
Snakes of the genus Chrysoplelea climb trees and then push themselves off with such force they can glide for distances of up to 100 meters (330 feet). Generations of evolutionary pressure have given the reptiles the power to flattened their shape for better aerodynamics. They also undulate in the air, as countless nature documentaries have revealed. Scientists were uncertain whether these movements help them gain greater distance, or were a holdover (which biologists call a spandrel) from when their ancestors moved in a similar manner across desert sands, as other snakes still do today.
Virginia Tech PhD student Isaac Yeaton used a high-speed motion capture camera and infrared markers placed along the body of a paradise tree snake (Chrysopelea paradise) to study this question. He found the movements involve waves in both horizontal and vertical directions. In Nature, Yeaton and co-authors reveal the motions stabilize the snakes’ flight through the air, preventing them from rolling uncontrollably.
When snakes, eels, and creatures of similar body shape undulate it is usually a way to push against the ground or water to create net forwards motion. However, pushing against air would not justify the energy expended. The fact Chrysoplelea move their bodies fairly slowly while in flight, with a frequency of 1-2Hz, adds to the impression this has more do to with force of habit than gaining distance. Experiments have also shown snakes of non-flying species undulate in a similar manner by reflex when dropped from a height, even when it does not help them.
Despite these indications, Yeaton found Chrysopelea really does need to undulate if they are to fly. Although modeling showed a creature with C. paradise’s body shape would be stable launching from 10 meters (33 feet) 50 percent of the time while keeping the body still, this rises to 94 percent with undulations. The benefits increased further when starting from a greater height, with longer, as well as more stable, glide paths.
Moreover, flying snakes have created a unique movement, unlike those used by their counterparts on the ground or in the water. The vertical waves have twice the frequency, but much smaller amplitude, than the horizontal equivalent.
Although they are rainforest creatures, the snakes need to make such long leaps to find unsuspecting prey because they prefer to inhabit the edge of clearings where there is more sunlight, but trees are further apart.
The work could prove useful to makers of flying robots, particularly any who wish to haunt our dreams by making their creations limbless.
For the record Chrysopelea are considered only mildly venomous, but you could probably still die of fright if one drops on you.