The Main Squeeze

When a screenwriter wants to put the hero in danger, what could be better than to throw some venomous snakes in his path? So movie cowboys wake up to find a rattlesnake staring them in the eye, and Indiana Jones faces down a pit full of asps. But venomous snakes are a small minority of all snake species. Most snakes kill their prey by constriction. And some new research has pointed out just how deadly that can be.

When a constrictor strikes, it quickly wraps its body around its hapless victim and squeezes it to death. The prey, whether it’s a rat caught in a black snake’s coils or a deer grabbed by an anaconda, is pinned inside a mass of solid muscle. As the prey struggles, the snake squeezes harder. Death usually comes within seconds.

This was the confusing bit. It was long assumed that constricting snakes killed by suffocation – having your ribcage squeezed certainly makes it hard to breathe – but death by suffocation usually takes several minutes, and these snakes could kill much faster than that. A few scientists had suggested that the snakes might squeeze hard enough to interfere with the prey’s circulatory system, but no one had been able to measure how hard a snake could squeeze.

Brad Moon changed that. Several years ago he developed a technique that let him measure a snake’s constriction strength – he implanted pressure transducers in mice, then let gopher snakes capture and eat them. He found that the snakes could squeeze at pressures as large as 232 mm Hg, well above the top pressure produced by mouse hearts (around 125 m Hg). When a snake wraps itself around a mouse, it effectively squeezes its heart shut.

Gopher snakes are about three feet long. What kinds of force can a really big snake produce? Moon recently had the chance to find out. Working with National Geographic, he measured constriction in an 18-foot long anaconda. The pressures this snake could exert could cause cerebral aneurysms, or snap the backbone of a large animal like a capybara or a deer. Moon thinks that these large snakes aren’t deliberately breaking the backs of their prey – it’s just a fortuitous side effect of their size and the mass of muscle they use in the squeeze. The cerebral aneurysms are probably what they’re really after.

Important safety tip. Stay far away from large snakes.

Moon presented these data at the annual meeting of the Society for Integrative and Comparative Biology earlier this month. I tried to blog about it direct from the conference, but the hotel had a lousy internet setup. Sigh. Maybe next year.

Comments

[gaw3]

Very cool, thanks. I've got three little boys, so predators are a hot topic around here.
There was a news item last fall about a boa which swallowed a croc before it was completely dead. Maybe crocodile brain vessels can survive the overpressure unusually well?

[DianeAKelly]

Well, it's not really clear what happened in that case. We know that someone walking through the Everglades found the burst-open carcass of a 13-foot long Burmese python with a 6-foot long American alligator spilling out of its guts. It's not clear whether the alligator was still alive when the snake swallowed it, since both animals were quite dead when they were discovered. It's possible that the 'gator lived long enough to damage the snake's gut, but it's also possible that the snake tackled a meal that was just too big for its stomach.