18 January 2012

Scientists have discovered how Boa Constrictors know when to stop squeezing their victims, according to research published today in Biology Letters.

Researchers based at Dickinson College in the US used partially reanimated dead rats – which were warmed up and fitted with a device mimicking a beating heart – to investigate how Boa Constrictors work out when they’ve killed their prey.  Constriction requires an enormous amount of effort on the snake’s behalf, so scientists were curious to find out how they avoid wasting effort when preying on small mammals, lizards and birds.

The scientists discovered that the snakes actually monitor their victims’ heartbeats, releasing the unfortunate animal as soon as its heart stops beating.  However, the researchers point out that their findings raise further questions, stating that “These findings are interesting, but seem to conflict with what we know about the physiology of endothermic [warm blooded] prey animals.”  Warm blooded animals tend to die fairly quickly once ensnared by a boa constrictor, so the research raises questions over why the snakes have evolved such a sophisticated mechanism for ensuring that their prey are dead.

One possibility is that heartbeat detection helps the snakes dispatch cold-blooded prey like lizards.  These creatures can survive for much longer when being strangled by slowing down their heartbeat and remaining completely still, so the snakes’ heartbeat detection could help them work out exactly when to release their cold-blooded prey without risking their escaping.  Another possibility is that the snakes are simply very good at detecting heartbeats as a result of their limbless lifestyle – slithering along the ground has allowed them to evolve highly developed tactile abilities, which they now use to grisly effect in finishing off their prey with perfect timing. 

Either way, the research has certainly made clear that snakes may be more sophisticated than previously thought, with lead author Dr Scott Boback commenting: “Many of us think of snakes as audacious killers, incapable of the complex functions we typically reserve for “higher” vertebrates.  We found otherwise and suggest that this remarkable sensitivity was a key advancement that forged the success of the entire snake group.”