What a mouthful! How boa constrictors don’t suffocate while eating

In what’s clearly a growing field of study, scientists recently explained how whales don’t drown while eating. And, until now, it hasn’t been clear how modern snakes save themselves from suffocating while eating. Using different regions of the rib cage when inhaling had been considered, but no one had monitored in detail boa constrictor breathing patterns while they throttled their next meal.

“With no diaphragm, they rely entirely on motions of their ribs,” says lead author of a new study, research scientist in the Department of Ecology and Evolutionary Biology at Brown University, USA Dr John Capano.

The study shows that boa constrictors can move only specific segments of their ribs, allowing them to breathe with certain segments of their lung when others are hindered by constriction. They can even use the hind section of their lungs like a bellow, pulling air into the lung when the ribs further forward cannot move.

The researchers attached tiny metal markers to two ribs in three adult female boa constrictors, one a third of the way along the body and the other in the middle. They then positioned a blood pressure cuff over the ribs in the regions of the metal markers and gradually ramped up the pressure to immobilise them. They used X-rays during this process to see how the snakes’ ribs moved.

“Either the animals did not mind the cuff, or became defensive and hissed to try to get the researcher to leave,” says Capano, explaining that the reptiles really fill their lungs when hissing: “this was an opportunity to measure some of the biggest breaths snakes take.”

They found that boa constrictors could control the movements of ribs in different areas of the rib cage independently by activating the musculature around specific ribs. For instance, when the blood pressure cuff was constricting them a third of the way along the body, they breathed using ribs further back – specifically, they swung these ribs backward while tipping them up to draw air into the lungs.

Then, when the ribs further back were being constricted, they breathed using ribs closer to the head. Interestingly, the ribs at the far-back end of the lung only moved when the forward ribs were constricted.

These worked to draw air deep into the region, despite the area having a poor blood supply and therefore not providing the body with oxygen. Instead, the area behaved like a bellow; pulling air through the front section of the lung when it couldn’t breathe for itself.

Subduing and digesting their prey is one of the most energetic things these snakes can do, so it was likely essential that they evolved this ability before adopting the constricting lifestyle, to ensure they didn’t suffocate while doing so.

The research was published in Journal of Experimental Biology.