Snakes, invertebrates, birds, and more have evolved several reasons for feigning death.
Of all the ways animals have evolved to evade predators, feigning death might be one of the most creative—and risky.
Scientifically known as thanatosis, or tonic immobility, playing dead occurs across the animal kingdom, from birds to mammals to fish. Perhaps the most famous death faker is North America’s Virginia opossum, which opens its mouth, sticks out its tongue, empties its bowels, and excretes foul-smelling fluids to convince a predator it’s past the expiration date.
Guinea pigs and many species of rabbits pretend to have perished, as do a number of snakes, such as the Texas indigo snake. Avian imposters include Japanese quail, domestic chickens, and wild ducks. Some sharks even pretend to go belly up: If flipped on their backs and momentarily restrained, lemon sharks will go limp, displaying laboured breathing and occasional tremors.
Dozens of invertebrates practice tonic immobility, making them among the most common—or at least most studied—species to do so.
For instance, when approached by a predator, pygmy grasshoppers in Japan will play dead by sticking out their legs in several directions, making it nearly impossible for frogs to swallow them.
In general, scientists don’t know enough about this intriguing behaviour, Rosalind Humphreys, a postgraduate student at the University of St. Andrews, Scotland, says by email. It’s difficult to record in the wild, and there are ethical concerns about creating lab experiments in which predators attack prey, she says. Here’s what scientists do know.
“The last chance”
Many insects feign death after a predator has grabbed them, a phenomenon called post-contact immobility.
For instance, the larvae of Euroleon nostras antlions—a fierce type of predatory winged insect—can play dead for an astonishing 61 minutes. Charles Darwin, on the other hand, was surprised to note a beetle that played dead for 23 minutes.
It goes a little like this: A predator, let’s say a hedge sparrow, notices a group of antlion larvae pits and dives to grab the insect. The sparrow drops the larva, as happens with some frequency, and the insect plays dead. (Learn about five more trickster animals that feign death.)
“It’s the last chance of your life,” says Ana Sendova-Franks, a visiting fellow at the U.K.’s University of Bristol and a co-author of a March 2021 study on the behaviour in the journal Biology Letters.
Post-contact immobility is different from momentarily staying still, “like when a burglar enters your house, and you freeze on the spot to protect yourself from being seen,” says Sendova-Franks. Instead, it’s often an involuntary physiological change, such as slowing the heart rate.
Playing dead for food or sex
While most creatures play dead to escape death, others have found alternate uses for the technique.
Take the nursery web spider. Females often prey on males, so to mate, the male makes a bundle of food, attaches himself to it, and pretends to be a goner. The female then drags around the food and supposedly dead male. When she begins eating the food, the male comes back to life and tries mating again—sometimes successfully, says Trine Bilde, a biology professor at Aarhus University in Denmark.
“Death feigning seems to be a male mating effort in addition to/or instead of being an anti-predatory strategy,” she writes in an email. “Perhaps it serves both functions.”
On the other end of the spectrum is the female moorland hawker dragonfly, which goes to great lengths to avoid mating: She’ll stop flying and crash to the ground to escape aggressive males, which can harm her.
The Central American cichlid pretends to be dead on lake bottoms to lure fish and other prey, When another fish comes in to take a bite of the carcass, the cichlid awakens and strikes. Similarly, the comb grouper of Brazil fakes its own death to attract young fish.
An odd, but successful, defence
Tonic immobility can seem “odd as a ‘last resort’ defence, given that we would expect prey animals to want to struggle and get away,” Humphreys says. “However, there are a number of means by which [tonic immobility] might succeed in reducing the likelihood of further attack.”
For instance, in the British antlion experiments, scientists found larvae that played dead longer than other larvae were less likely to be eaten by a predator, which was either fooled or simply frustrated by the larvae’s response. (This is why insects rule the world.)
In a 1975 experiment, scientists observed how captive red foxes preyed on five different duck species, most of which would play dead immediately when caught. The foxes then carried the ducks back to their dens to eat later. Experienced foxes knew to kill or maim the ducks immediately, but inexperienced foxes sometimes left the supposedly dead ducks, allowing their quarry to escape.
That’s why Sendova-Franks calls the behaviour a last chance. Moving guarantees death, but playing dead offers a possibility—however small—of survival.
