Anyone planning a fright for Halloween might learn a trick from a South American frog that dramatically fakes its own death, according to scientists.
Leaf litter frogs (Ischnocnema aff. henselii) of southern Brazil were recently observed playing dead by turning belly-up, shutting their eyes, and throwing back their arms and legs. The frogs stayed in their exaggerated death pose for about two minutes, according to a team lead by biologist Vinicius Batista of the State University of Maringá in Brazil and reported in the fall issue of the Herpetological Bulletin.
The behavior has not been seen before in this species, and it’s more dramatic than scientists are used to seeing in other animals. But it’s not uncommon for frogs to play dead in some way, says Andrew Gray, curator of herpetology at the Manchester Museum, U.K.
Technically known as thanatosis, playing dead is a way to trick predators that watch for movement in potential prey. And as the nickname “playing possum” suggests, it’s not unique to frogs.
Fire-bellied toads from Asia and Europe also get dramatic in fake death. When playing dead, the toads (which are scientifically classified as frogs) arch their backs and contort their limbs to display yellow or orange warning markings on the undersides of their feet. They may also flip onto their backs to show similar markings on their underside (hence the name fire-bellied toad).
“It’s a warning not to eat them because they’ve got these strong toxins in their skin," Gray says.
It’s thought that the lack of movement caused by thanatosis may focus a predator’s attention on such warning markings, or on foul-smelling odors.
Hognose Snakes and American Opossum
The American opossum (Didelphis virginiana) and hognose snakes from the North American genus Heterodon are two types of death-fakers that employ scents in their acts.
The snakes, which sometimes spew blood while playing dead, secrete a foul-smelling fluid from their anal glands during thanatosis.
“The message it’s giving off is that there’s something wrong with it,” Gray says.
The opossum also assaults a potential predator’s olfactory while playing dead. Dead animals may harbor dangerous bacteria and other harmful organisms, so many predators instinctively avoid eating them.
Nursery Web Spider
Among invertebrates such as ants, beetles and other insects, death-feigning is a fairly common survival tactic, but there’s also a spider that uses the behavior for sex.
During courtship, the male nursery web spider (Pisaura mirabilis) offers the female a silk-wrapped insect. If the larger female attempts to steal the food without mating, the male plays dead and is dragged off along with his gift.
“It seems as if death-feigning and hanging on to the gift allows him to stay close to the female,” says Trine Bilde, an evolutionary ecologist at Aarhus University in Denmark.
When the female starts feeding, the male comes to life and resumes its attempts to mate.
Bilde, who was the first scientist to record the behavior, says the nursery web spider is the only known animal that plays dead to induce mating.
Some preying mantid males freeze when trying to get away from cannibalistic females after mating, “but not to achieve mating,” Bilde notes. “So that would be an anti-predator behaviour.”
There are also predators that play possum. Two species of cichlid fish are known to pretend to be dying or dead to attract scavenging species as prey.
Lurking in Lake Malawi in East Africa, Livingston’s cichlid (Nimbochromis livingstonii) has been observed sinking to the bottom of the lake and lying motionless on its side, waiting for a moment to strike.
The fish’s blotchy coloring is thought to mimic a rotting carcass.
Any Halloween zombies out there might want to take note.