7 April 2021

The Science of Spitting Snakes

Some cobras have developed the ability to spit their venom from their fangs as well as inject it into their prey, but has evolution changed the formulation of the venom to make it more suitable for spitting?

Cobra

You don’t want to be the wrong end of cobra venom: it can be extremely dangerous, even fatal. However depending on the situation, species use their fangs to either spit their venom in defence or inject it into their prey as an attack.

But why are we talking about snake venom in Materials Science and Engineering? We’ll let Dr Chris Holland, Senior Lecturer in Natural Materials and PhD Student Edgar Barajas Ledesma, pick up the story.

“We’ve been working with academic colleagues from the University of Porto in Portugal and Liverpool School of Tropical medicine to understand the differences in the methods of venom delivery employed by cobras”, says Chris. “We thought that there would be differences in the flow properties of the venom to adapt to the method of delivery.

“Indeed, previous smaller-scale studies suggested that the faster the venom flows, the less viscous it is, making it a non-Newtonian fluid, like tomato ketchup and better for spitting. 

“However, our study, which involved measuring the properties of the venoms from 13 spitting and non-spitting cobras species, showed that, in fact, all venoms were Newtonian in behaviour, so there was no change in their flow properties when it was spat at speeds used  by the snake.

“We analysed the venom samples using a shear rheometer to detect any variability in the flow of the liquid when we caused it to flow. This is quite a common test in engineering applications, so it was interesting to get to use it for a more unusual research question.”

Interesting stuff, Chris, but what does this mean for the snake?

“So the material properties are much more straightforward that we initially thought they would be, but that doesn’t mean that the venoms are in any way simple”, continues Chris. “Venoms can contain more that 20 compounds, mainly proteins and polypeptides, resulting in a cocktail of proteins, enzymes, and various other substances with toxic and lethal properties. However despite their deadly origins, they can be used for good as there are several other compounds that are of interest from a medical and pharmacological perspective.”

Edgar Barajas Ledesma adds “For the snake, though, where we previously thought that they had evolved a venom more suitable for spitting, it turns out that there is a consistency in the fluid properties, and we have suggested that this consistency actually helps the snakes to hit their target.” 

But it does seem there are differences between spitting and non-spitting cobras. Edgar calculated the impact of venom viscosity and fang shape on the fluid pressure inside the fang and found that to eject venom required more pressure in the non-spitting fangs than the spitting fangs. However it is still no easy feat, Barajas-Ledesma adds “Spitting and non-spitting cobras still use the same pressure as a firehose to eject their venom, so perhaps it's not so surprising they need it to flow as consistently as possible”.

Thanks for that, Chris and Edgar. I’m still not sure that I want to encounter one of these deadly creatures any time soon!

This study has been published in the Journal of Experimental Biology, under the title of “Unexpected lack of specialization in the flow properties of spitting cobra venom”.