Bio-aerial Locomotion 2011

Say the word “glide” out loud, and you’re likely to think first and foremost of wings. Most gliding creatures have some kind of wing-like structure to aid in their battle against gravity, from the patagium of the flying squirrel to the wide, papery wings of the Javan cucumber seed.

Most, but not all.

Meet genus Chrysopelea, a group of five species of snakes that have developed the ability to glide, despite a lack of any kind of limb, appendage, or wing-like structure so slow their descent. Its secrets lie in the way it morphs and moves its body midair, producing aerodynamic forces that exceed the weight of the snake, giving it the spectacular ability to slither through the air.

Launch sequence from varying angles

The snake begins by hanging from a branch by its tail, making a J-like shape, from which it springs up and out. This springing gives the snake a bit more height from which to glide, as well as providing a little extra velocity boost, to help create lift. As it becomes airborne, the snake flattens its body from just behind its head to the vent by flaring out its ribs and contracting its stomach, creating a concave cross-sectional shape similar in many ways to an air foil. The snake then positions itself to have a high angle of attack, and begins to undulate laterally in an S-shape.

A- Normal body shape B- Flattened body shape. From J. Socha (2011). See References below.

Lift it caused by these combined factors: the increased surface area and air foil-like shape of the snake’s body when flattened, the high angle of attack the snake is able to take on, and the undulating of the body, which increases the velocity of the glide as the snake undulates with higher amplitudes. The best gliding species of these snakes, the paradise tree snake, is able to reach glide ratios as high as 4.2.

Pretty amazing  for a creature shaped more like a piece of rope than an airplane.

References:

• John J. Socha, Gliding Flight in Chrysopelea: Turning a Snake into a Wing, Integr. Comp. Biol. (2011) doi: 10.1093/icb/icr092
• Video credit: Dr. Jake Socha
• When Snakes Fly
• New Snake Footage Uncoils Mystery of Flying Serpents