The dice snake lies motionless with its bloody mouth wide open to pretend to be dead, confusing the birds of prey and allowing them to relax their claws, giving them a chance to escape.
When captured by predators, the dice snake on Golem Grad, an island in the middle of a lake in North Macedonia, fouls itself with a mixture of feces and pungent compounds. Then, they became motionless, their mouths wide open, their tongues sticking out. Finally, to complete the act of pretending to be dead, some animals even vomited blood. This snake’s use of blood to fake death may be the key to creating a convincing performance, according to research published on May 8 in the journal Biology Letters.
Many species in the animal kingdom play dead when disturbed by predators, including insects, fish and reptiles. Even mammals do it. The great effectiveness of feigning death comes with high risks, according to Vukasin Bjelica, a PhD student at the University of Belgrade and author of the paper.
Some predators appear confused or frightened when they see another animal suddenly immobile, especially if they are smelly and bleeding. Other animals may stop watching closely and relax their claws, giving prey time to escape. But that requires the performing animal to lie still while someone wants to eat it. Therefore, the prey has an incentive to find ways to shorten the time it takes to pretend to be dead.
Bjelica’s research focuses on dice snakes, a non-venomous fish-eating snake that ranges from Western Europe to western China. They have many self-defense techniques, including biting, bulging and flattening their heads to imitate venomous snakes. But snakes on Golem Grad Island often pretend to be dead to deal with their main enemy, birds.
The research team led by Bjelica caught and examined 263 snakes, chasing them and catching them mid-flight to provoke a variety of defensive behaviors. While being careful not to hurt the snakes, they grabbed them, gently squeezed them and stretched them on the ground to simulate a hesitant predator and recorded the dice’s reactions.
They found that captured snakes tried to smear feces and pungent compounds all over their bodies (50% of snakes), spit blood from their mouths (10%), and pretended to be dead. Some snakes get quite stressed when playing dead, making it difficult for them to move. Others lay so still that the students could arrange them in the shape of a heart.
According to Bjelica, they were really dedicated to pretending to be dead. The strategy seems to be most effective on adult snakes. Immature dice snakes that are caught by birds rarely take risks and pretend to be dead in a much shorter time. The tactic also works when there are many other prey around, causing the predator to be distracted and not pay attention to the snake pretending to be dead.
However, because most of the data comes from a relatively specific population, that is, island snakes that are hunted by birds, Mr. Bjelica believes that further research on snake populations elsewhere is needed.