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updated 1/18/2012 1:20:42 PM ET 2012-01-18T18:20:42

Snakes do not just kill on instinct, but they instead monitor the condition of their victims right until the very end.

The tightness and duration of a constricting snake’s death squeeze are timed to perfection, matching the heartbeat and weakening state of the snake’s unfortunate prey, according to a study published in the latest Royal Society Biology Letters.

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The findings reveal that snakes are far more intelligent than previously thought, capable of complex functions typically reserved for “higher” vertebrates. They are also master hunters, ready to kill at any given moment.

“A snake first detects its prey with visual and chemosensory means,” lead author Scott Boback, an assistant professor of biology at Dickinson College, told Discovery News. “In addition to these, Boas also have heat sensitive neurons located beneath their lip scales. These neurons can sense temperature differences in their environment, such as an endothermic prey animal.”


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“They can kill their prey through a variety of means, including constriction, envenomation or a combination of both,” Boback added.

For the study, Boback and his colleagues caught 16 wild Boas, raising them in a temperature-controlled lab on a diet of dead chicks and rats. Some rat cadavers were outfitted with a simulated heart that permitted the researchers to control how it pumped.

The scientists next dangled the warmed, outfitted rats tantalizingly over the snakes. As the snakes went into their death grip, Boback and his team analyzed the pressure generated by the snakes. The snakes responded to the beating heart, constricting longer and with greater total pressure until the heartbeat ceased.

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This video shows a boa striking and constricting during a kill.

Snakes naïve to live prey also responded to the simulated heart, suggesting that the behavior is partly innate. But experienced snake hunters perfectly timed their kills to the heartbeats.

“That suggests to us that snakes can learn how to change their constriction duration and pressure to effectively kill their prey,” Boback said.

He also explained that since snakes use a variety of cues to monitor the state of their victims, they would not waste their time squeezing an animal that does not die after a certain period of time. During the study, if the researchers kept the simulated heartbeat in the rat cadaver going, the snake did eventually release the rodent.

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The scientists suspect that snakes evolved their acute detection abilities to deal with tricky prey. Iguanas, for example, can remain submerged in water for up to 4.5 hours, slowing their heart rate and oxygen needs. A variety of lizards, snakes and crocodilians can also survive anoxia for up to 1.5 hours.

It can therefore prove difficult to confirm the death of certain prey based on cessation of muscular or lung movement. Cardiovascular function turns out to be a more reliable cue.

Prior research suggests that many snakes pay attention to the heartbeats of others, with the ability being widespread in constricting species.

Warren Booth, an integrative molecular ecologist at North Carolina State University, informed Discovery News of another Boa snake skill: Females can give birth as mate-less virgins.

Booth said genetic confirmation of virgin birthing, technically known as parthenogenesis, has been confirmed in “boa constrictors, rainbow boas, various shark species, Komodo dragons, and domestic turkeys, to name a few.”

Boback and his colleagues suspect many such snake abilities evolved early on in the snake lineage, perhaps going back to the Late Cretaceous.

© 2012 Discovery Channel

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