It’s conventional wisdom that the snakes who eschew venom for a squeeze do in their prey by coiling around them so tight that breathing is no longer an option. New research published this week in the journal The Company of Biologists overturns that conventional wisdom — constrictors want hearts to stop beating, not lungs to stop breathing.
Scott Boback studies snakes at Dickinson College in Carlisle, Pennsylvania and is the lead author on the latest squeezing study. It’s actually the second time Boback has found something surprising about constrictors. Back in 2011, Bobak and his team discovered that when the snakes are coiled around prey, they don’t just squeeze for a certain amount of time and then check for a pulse — constrictors wait for an animal’s pulse to flatline before letting go.
For that study, Bobak filled dead rats with artificial hearts and let some boas do their thing. For the most recent study, he and his team rigged up anesthetized rats with instruments measuring blood pressure and heart activity to see what really fails first: the lungs or the heart.
It turned out that the captive boa constrictors squeezing the cyborg rats didn’t need to squeeze hard enough to inhibit breathing, just blood flow. “A boa constricting a small rat is generating the kind of pressure that would stop the blood flow in your arm,” Bobak told National Geographic.
Still, even a moderate wrap proved enough to fatally disrupt blood flow. You’d unconscious in just a few moments if something wrapped around your neck and prevented blood from resupplying your brain. It would happen even faster for a mouse, indeed this is precisely what happened in the study, and that’s what the snakes have evolved to count on.
Constriction is a brute-force way to go, and energy-intensive. The faster a snake can render an animal unconscious, the faster the danger of thrashing prey dissipates. Suffocation is a slow process, fainting is not, and a boa, though incredibly strong, still doesn’t want to restrain struggling teeth, claws, hooves, and beaks longer than it has to.
The snakes seem to squeeze only as hard as they have to to induce unconsciousness, quickly followed by death, and not hard enough to make sure each breath is harder to draw. It’s a sleek way to apparently strangle prey.