Boa constrictors kill prey by quickly stopping their blood flow, according to a new study which busts the longstanding myth that the large, heavy-bodied snake suffocates its prey to death.
The study found that rats attacked by boas do not die from a lack of air. Instead, the boa's tight coils block the rat's blood flow, leading to circulatory arrest.
The deadly grip helps to more quickly subdue rats and other prey that might be clawing back, allowing the snake to quickly end the struggle and preserve its energy, the researchers said.
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It is not surprising that it was suspected that the Boa constrictor used suffocation to kill prey, said lead researcher Scott Boback, an associate professor of biology at Dickinson College in Pennsylvania.
Oftentimes, it looks like prey is gasping for breath as it fights against the snake's hold, Boback said.
But two studies - one published in 1928 and the other in 1994, the latter written by Dr David Hardy, an anesthesiologist who studies snakes - suggested otherwise.
Suffocation can take minutes to kill a rat, whereas circulatory arrest can lead to death within 60 seconds, Boback told 'LiveScience'.
"What Hardy saw was the speed at which the animals were dying. They were dying way too quickly for it to be suffocation," said Boback.
"He suspected that it was circulatory or cardiac arrest because of the speed at which death was occurring," he said.
Boback and his colleagues tested how anesthetised rats responded to boas' constriction.
They implanted electrocardiogram electrodes to measure the rats' heart rates, and inserted blood pressure catheters into a major artery and vein in each rat.
They also inserted a pressure probe, and took a blood sample from each of the 24 rats, before placing them, anesthetised, next to the hungry snakes.
The snakes struck quickly, biting the rats' heads and wrapping their bodies around the prey. The sensors embedded in the rats showed that the rodents' circulation shut down within seconds of the attack, Boback said.
The rats' arterial pressure dropped, meaning their hearts had trouble pumping oxygenated blood to the rest of their bodies. Meanwhile, their venous pressures rose, suggesting that the snakes' constriction applied a pressure that was too high for the blood to return to the heart.
Blood samples also showed that the rats' potassium levels skyrocketed, likely leaking from burst cells and thus indicating cardiac arrest. The researchers didn't measure the rats' brain activity, but the lack of blood to the brain also likely hastened the rats' deaths, Boback said.
The study was published in The Journal of Experimental Biology.
