Flying snakes' secret found: biologist

A Virginia Tech biologist has uncovered how flying snakes are able to glide as far as 21 metres through the air.
Biologists say Chrysopelea paradise snakes use tree branches to help launch themselves into the air. ((Jake Socha))

A Virginia Tech biologist has uncovered how flying snakes are able to glide as far as 21 metres through the air.

According to biologist Jake Socha, five related species of tree-dwelling snakes found in south and southeast Asia are able to fly by flinging themselves off high perches, flattening their bodies and gliding through the air.

Socha and his colleagues studied Chrysopelea paradise snakes, also know as the paradise tree snake or paradise flying snake, as they launched themselves off a branch atop a 15-metre high tower.

Four cameras recorded the snakes from different angles as they glided through the air, allowing researchers to create and analyze a 3D reconstruction of the animals' body positions during flight.

'Swimming through the air'

The reconstructions were coupled with an analytical model of gliding dynamics and the forces acting on the snakes' bodies.

"The snake, in essence, is one long wing. And so … it jumps off and it reforms its body, but then as it falls it starts to coil up and it starts to undulate," Socha said in an interview on CBC's Quirks & Quarks.

"So imagine making a big swooping 'S' and then that 'S' isn't held statically — instead, what happens is it's moving back and forth essentially from left to right…. It almost looks like it's swimming through the air."

The analyses revealed that the reptiles never achieved an "equilibrium gliding" state — one in which the forces generated by their bodies exactly counteract the force pulling the animals down, causing them to move with constant velocity at a constant angle from the horizon. Nor did the snakes simply drop to the ground.

Instead, Socha said, "the snake is pushed upward — even though it is moving downward — because the upward component of the aerodynamic force is greater than the snake's weight."

He added, "Hypothetically, this means that if the snake continued on like this, it would eventually be moving upward in the air — quite an impressive feat for a snake."

However, the research suggests the effect is only temporary, and eventually "the snake hits the ground to end the glide," Socha said.

'How do you land with no feet?'

Upon becoming airborne, the snake flattens out to double its normal width. ((Jake Socha))

He added that it's still not clear exactly how the snakes control their gliding behaviour.

"It's likely that if … the snake were not undulating and constantly changing the shape, that it would probably roll out of the sky. It would probably tumble and fall to the ground," he said.

"So I think that maybe this undulation back and forth gives the animal some dynamic stability that keeps it in a posture so it doesn't lose control.

"Now another question when you talk about this manoeuvring … they seem to do it on purpose and they seem to decide to turn, so how does it do that? And to tell you the truth, I don't have any clue how it does that."

Another mystery, he said, is how flying snakes execute their landings.

"All other flyers have legs and when they land, they can reorient their body so it's favourable for them to land feet first. So how do you land with no feet?" he said.

"I don't know exactly how they land, but I can tell you some things that they're not doing. One, they don't slow down, so when they hit the ground or tree or whatever they're landing on it seems to be at the same speed as their glide.

"And two, they don't appear to massively reorient the body, with one exception — it seems that if they have enough space and they land on the ground, they seem to drop their tail down first, almost like their landing gear, and the very last thing that hits is their head."

While biologists still have a lot to learn about flying snakes, Socha said what they have uncovered is significant.

"It really is a quite sophisticated behaviour that this animal has. To me it seems pretty phenomenal that it's able to do this."