Boa constrictors are well-known for wrapping themselves around prey when moving in for the kill. However, these animals take the lives of their victims by cutting off the target's supply of blood, not air, a new study reveals. Previously, most biologists believed the powerful grip of the snake caused the target to suffocate.

Researchers examined the blood pressure and heart rate of rats as the rodents were killed by the snakes. The prey animals were provided with an anesthetic beforehand to prevent suffering. Investigators learned that death by boa constrictor is relatively quick and efficient. The rodents became unconscious within seconds of the start of an attack, the study noted. Compression by the boa cuts off blood that would have carried oxygen to vital organs including the heart and brain. These actions kill the prey animal in much less time than if the snake had to wait for the target to die of asphyxiation.

Investigators believe this is the first time such a study has been carried out, detailing methods by which boas take the lives of their victims.

"If the snake is wrapping around the chest, it could also be limiting breathing, too. But an absence of blood flow will cause death more rapidly than suffocation," said Scott Boback of Dickinson College in Pennsylvania.

The snake started attacks by biting into the neck of the intended victim, and wrapping itself around the body of the target. Within seconds, circulation in the rats shut down. Arterial pressure dropped, and pressure in the veins rose. Heart rate quickly rose, and became irregular. Researchers believe the lack of fresh blood in the brain caused the rats to fall unconscious before vital organs failed, bringing about death. The animals were examined after death, in an effort to better understand the process.

Blood samples were taken from the rats before and after death to record changes in oxygen levels. This examination could serve to advance treatment methods for people recovering from crush-related injuries, such as car wrecks.

Learning how boas kill they prey could also offer new insights into the evolution of these snakes, as well as other species. It is possible that the ability to carry out constriction allowed the snakes to hunt larger animals.

"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.

Analysis of how boa constrictors kill their prey was detailed in The Journal of Experimental Biology.

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