Sorry, boa constrictors, we've misjudged you

When a boa constrictor catches a rat, lizard or bird, the snake seems to suffocate the animal before devouring it. But new research finds that's not actually the case.

"It looks like the animals are gasping for air," said Dickinson College's Scott Boback. But a theory put forth by colleague Dave Hardy that has been the talk of snake enthusiasts but never proven - that the boa kills by constricting the blood flow of its prey - seemed like a more promising explanation. So Boback put it to the test.

"What Hardy saw was the speed at which the animals were dying... they were dying way too quickly for it to be suffocation. He suspected that it was circulatory or cardiac arrest because of the speed at which death was occurring," he said.

With little data to back up the theory, Boback went to work, setting up experiments where he measured the blood pressure of sedated rats as they were being squeezed by a hungry boa constrictor. (He assured the hapless prey couldn't feel a thing.)

By putting ECG electrodes and blood pressure catheters into the rodent's body, Boback and his colleagues could track the rodent's vital signs as it was devoured. The thing that jumped out: The rat's blood circulation shut down in seconds.

"I remember being in the room and the students were looking at the data in disbelief that it happened that fast," Boback said. "We could see the arterial pressure go down, the venous pressure go up and we could see this right when the snake was doing it (squeezing). As soon as the rat's circulation stopped and the oxygen supply was cut off, the team could also see the rat's heart beating more and more irregularly."

Boback concluded that boa constrictors - and other constricting or crushing snakes - kill their prey by cutting off the blood supply to the heart, brain and other vital organs and thus causing their victims to pass out in a matter of seconds and die. His findings appear in The Journal of Experimental Biology.

Michael E. Dorcas, the Nancy and Erwin Maddrey Professor of Biology at Davidson College who didn't take part in the study, called the findings "very cool."

"This is excellent research that dispels the common and long-held notion that constricting snakes slowly suffocate their prey," Dorcas told CBS News. "Some prey are potentially dangerous and could injure snakes during constriction and thus, it makes sense from an evolutionary perspective that if you are capable of incapacitating your prey quickly by squeezing it with a lot of force, you should do so."

Boback said the findings could help scientists gain a better appreciation of this behavior in snakes, as they have increased the size of their prey in more recent times. Ancient snakes, some of which didn't kill by constriction, were probably limited to smaller prey, he said.

"By understanding the mechanisms of how constriction kills, we gain a greater appreciation for the efficiency of this behavior and the benefit it provided early snakes," Boback said.