Physics of Snake Venom

Its physical properties as a fluid are as perilous as its chemical composition

The effectiveness of snake venom at achieving its designated task, immobilising or killing prey, seems to be connected with its physical properties, which appear to matter as much as its chemical ability to stun or kill. It has long been known that some snakes such as cobras inject venom directly into their victim’s body through hollow poison fangs, but researchers  Leo von Hemmen, a biophysicist at the TU Muenchen, and Professor Bruce Young, a biologist at the University of Massachusetts, Lowell, working on snake hearing have found that this is true only for a fraction of poisonous snake species—only one-seventh, to be precise. 

The vast majority of snake species lack these fangs and instead punch holes into victims’ skin and then let the venom flow out onto the prey and enter the wound. This is true of many Indian snakes such as the mangrove pit viper found in Assam. The problem with the method is that snake venom is a thick viscous liquid that should not flow with any ease to enter the wound in sufficient quantity to have impact. The researchers found that ‘snakes developed a trick in the course of evolution: when a snake attacks, the fang grooves and the surrounding tissue form a canal. Just like blotting paper, the tissue sucks the venom through this canal. And snake venom has a very special property to facilitate this effect: just like ketchup, which becomes significantly more fluid upon shaking, the sheer forces that arise from the suction cause the venom to become less viscous, allowing it to flow through the canal quickly as a result of the surface tension’.

‘Scientists refer to substances with these characteristics as non-Newtonian fluids. These have a very practical consequence for snakes: as long as there is no prey in sight, the venom in the groove remains viscous and sticky. When the snake strikes, the poisonous “tears” flow along the groove—just like wine along a glass—and into the wound, where the venom takes its lethal effect.’

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