Dice Snakes Make Playing Dead Even More Dramatic

Dice snakes are not the only animals to use playing dead as a defensive tactic, but certain particularly theatrical individuals have been observed taking the performance to extraordinary lengths.

As well as lying limp with their mouths open, dice snakes (Natrix tessellata) deploy some remarkably unpleasant effects. They may defecate and rub the faeces over themselves, release foul-smelling musk, and even bleed from the mouth, creating what may be nature's most convincing imitation of death.

Although this behaviour can look excessive, it appears to bring an advantage. Scientists investigating these highly developed performances found that snakes adding these extra touches could escape sooner, avoiding predators more effectively than those that did not make the additional effort.

"Our results," write zoologists Vukašin Bjelica and Ana Golubović of the University of Belgrade in Serbia, "highlight the functional integration of antipredator behaviors across different phases of predator-prey interactions, emphasizing the need for future research to prioritize studying the sequential display of behaviors."

Dice snakes and apparent death

Apparent death, also called tonic immobility, occurs widely throughout nature and across numerous taxa. Its prevalence indicates that it is an effective anti-predator response, though the precise reason remains uncertain. Some studies indicate that it is commonly a final attempt to get away once a predator has already made contact with its prey.

Whatever the mechanism, some snakes appear to have pushed the odds further in their own direction. Eastern hog-nosed snakes (Heterodon platirhinos), for instance, roll onto their backs, convulse, vomit and release musk. This unpleasant-smelling material is produced by glands close to the snake's cloaca, resembling the anal glands of skunks.

Dice snakes, a non-venomous species whose diet consists mainly of fish, are already known to use faeces and musk in their defensive arsenal. When disturbed, they wriggle, hiss and cover themselves in odour. They also feign death and have been recorded bleeding from the mouth through a capability called autohaemorrhaging.

Their range extends across western Europe, northern Africa, the Middle East, Central Asia and western China. They are also a desirable meal for many predators, including reptiles, birds and mammals.

Studying dice snake defences in the wild

Bjelica and Golubović set out to examine how the snake's defences operate in natural conditions. On the Macedonian island of Golem Grad, they quietly approached and startled snakes in their habitat.

The researchers disturbed 263 snakes by grasping them around the middle and recording their reactions. Almost half of the animals - 124 - defecated, while a far lower number - 28 - bled from the mouth. Autohaemorrhaging was observed only in snakes that also feigned death.

When the team calculated how long each snake remained motionless, however, they found something notable. Snakes that enhanced their death display spent roughly two seconds less pretending to be dead.

The researchers say this indicates that combining defensive tactics gives the snakes an additional benefit: those making the extra effort can leave sooner. Examining how behaviours function together, they add, could reveal much more about animal defence.

"Our findings provide evidence for the functional integration of distinct antipredator behaviors across sequential phases of the predator-prey interaction (musking during the capture phase and death-feigning and autohemorrhaging during the post-capture phase)," the researchers write.

"Consequently, future research should prioritize examining the precise sequence of behaviors displayed during experiments rather than focusing on isolated displays."

Every snake involved in the study was released unharmed where it had been captured.

The research was published in Biology Letters.