Unraveling the Mystery of Boa Constrictors’ Breathing Techniques During Prey Constriction

Researchers outfitted the snakes with electrodes and scanned them using X-rays to see how the flexing predators managed to take in air

Boas constrict their prey to death.

When coiled around a lizard or throttling a bird, a boa constrictor doesn’t actually suffocate its prey. Instead, the snake squeezes the unfortunate victim to death by cutting off the target’s blood circulation. But scientists have often wondered how the snakes themselves keep from suffocating during the process. Somehow boas are able to keep breathing, even while their own lungs are tightly squeezed during constriction and unable to get air normally.

Now a study published today in the Journal of Experimental Biology has uncovered the secrets of boa breathing. In it, researchers show how the adaptable serpents shift to a different style of respiration, using the rear parts of their long lungs and bodies to keep oxygen flowing even while putting a deadly squeeze on their victims. The authors theorize that boas’ incredible breathing adaptations may have evolved far back in their history, and enabled them to later adopt their effective method of subduing and devouring prey.

When not constricting prey, boas breathe by motions of their ribs, expanding and contracting the surrounding muscles in accordion-like fashion to fill their lungs and exhale again. This breathing typically occurs near the front of the snake, around its heart. But the snakes use that same section of body and ribs to squeeze the life out of a bird or small mammal, and when locked down around such prey this part of the snake’s body is unable to move or to provide oxygen as usual.

Scientists had witnessed the snakes’ bodies moving in varied ways during hunting and feeding and wondered what exactly was going on. “Watching animals constrict we were seeing that they were kind of breathing with regions that were different than when they were resting, using those regions further back on the body, so we built out an experiment to kind of tease that apart,” says ecologist John Capano of Brown University, who co-authored the new study.

Capano says scientists had puzzled for years over the snakes’ very long lungs, and the breathing adaptations they enabled, especially since a part of their rear lung is a balloon-like bag without enough blood vessels to be effective in delivering oxygen to the bloodstream. His group suspected that the snakes were able to alternate which parts of the ribcage and lungs they used to breathe, depending on whether they were lying around resting, squeezing the life out of a lizard, or digesting an enormous meal.

To find out how the snakes managed it the group used some constriction methods of their own. The researchers applied blood pressure cuffs to the ribs of boas to prevent them from breathing with certain sections of their ribcage at a given time. “We created a scenario to emulate what happened with constriction, just preventing the rib cage from being able to expand any more, and recreating what we’d seen them do when constricting and eating in a natural setting,” Capano says.