RESEARCH: Snakes know how much venom they have and they won’t attack if they don’t have enough

Not all snakes are venomous, but scientists at the Chinese Academy of Sciences in Chengdu wanted to know more about venomous snakes.

The researchers studied venomous Sharp-Snouted Pit Vipers (Deinagkistrodon acutus). The New Scientist magazine (22 June 2021) reported the research results.

The aggressive Sharp-Snouted Pit Viper may be able to sense how much venom it has and it won’t attack if it doesn’t have enough venom (poison). 

Previous research indicates that venomous animals, including spiders, scorpions, and snakes, use their venom frugally and carefully because they do not produce a lot of venom. However, previous research did not study the possibility of whether venomous snakes save their venom for specifc situations, such as self-defence.

Scientist Yige Piao and colleagues at the Chinese Academy of Sciences have now shown that Sharp-Snouted Pit Vipers appear to behave differently when threatened depending on their venom levels.

The researchers housed 23 juvenile snakes in separate boxes, dividing them into three groups defined by their venom levels: low, replenishing, and normal.

The low and normal venom groups followed a three-day testing cycle over 24 days. 

For the first two days of each cycle, the research team enticed individual snakes in the low venom group to bite into a cloth once each day to ensure that the snakes had little venom. 

The normal venom group experienced a blank test, during which the snakes were gently poked instead. 

Every third day, all snakes underwent a behavioural trial.

The replenishing venom group initially followed the same pattern as the low venom group. But for the final three testing cycles, the researchers gave these snakes four days of rest after each behavioural trial to allow them to replenish (refill) their venom naturally.

During the behavioural trials, each snake was provoked for a minute using a piece of medical silicone skin at the end of a snake hook. Snakes responded by sounding a warning (such as a hiss), fleeing (sliding away), or attacking (striking and injecting the silicone skin with venom).

The results of the experiment showed that snakes with normal venom levels performed more strikes overall. Conversely, low-venom snakes showed more fleeing behaviour. The venom-replenishing vipers became more willing to strike in the second half of the experiment, when they were given more time to build up their venom levels.

The researchers say the results suggest that the snakes can sense their venom levels and tailor their response to a threat accordingly.

“This conclusion makes considerable intuitive sense since many other venomous organisms are understood to ‘metre’ their venom,” says Timothy Jackson at the University of Melbourne in Australia. “I applaud the researchers – it is one thing to predict a phenomenon and quite another to demonstrate its existence in nature.”

“This carefully designed study certainly provides a lot of thought-provoking evidence,” says Arie van der Meijden at the University of Porto, Portugal. However, Arie van der Meijden said that fatigue, habituation, or hunger could also be factors that explain the results.

The snake researchers are confident that the experiments ruled out other factors. “Snakes were tested only once a day, so they got nearly 24 hours to relax, and their responses showed little sign of habituation,” says Piao, adding that there were enough “dry” bites and other defensive moves to suggest strikes were non-predatory.

So, researchers say that snakes know how much venom they have and they won’t attack an animal if they don’t have enough venom.

Journal reference: ToxiconDOI: 10.1016/j.toxicon.2021.06.003

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM

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