How a boa constrictor's deadly embrace works


A red-tail boa constrictor from the Amazonian forests swallows a mouse after squeezing it to death. Now scientists know how the process works.
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Scientists have finally worked out why snakes, such as boa constrictors, are so deadly in a somewhat macabre experiment using rats.

The researchers measured the cardiovascular function of (heavily anaesthetised) rats before, during and after being constricted by the snakes to determine the effect of constriction on the prey's circulatory function.

The results show that the process, whereby the boas immobilise and kill their prey, is as rapid as it is deadly.

Within six seconds of being constricted, peripheral arterial blood pressure at the femoral artery dropped to a half of baseline values.

Central venous pressure (CVP), meanwhile, increased 600% from baseline during the same time.

Electrocardiographic recordings from the rat's heart showed the heart rate plunged to nearly half of baseline within a minute of the snake starting to squeeze the life out of its victim.

By the end of the process the rat's PBP had fallen nearly 300% and nearly all the rats showed cardiac electrical dysfunction.

What is more, there were changes to the rats' blood chemistry during the process with potassium levels nearly doubling and the pH dropped from 7.4 to 7.0.

"Our results suggest that boas are subduing and killing their prey during constriction by significantly affecting the prey’s cardiovascular system," the researchers write in the Journal of Experimental Biology.

They believe that the snakes' technique is why they are such efficient killers.

"The snakes accomplish this by encircling their prey with loops of their bodies; pressure is then generated when this coil is reduced in diameter.

"We believe that this circumferential compression generated by snake constriction is especially effective because of the efficiency of energy transfer from this geometric shape change."

  1. http://jeb.biologists.org/content/218/14/2279.abstract
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