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Thanatosis — pretending to be dead — is one of the best strategies that certain wild animals came up with in order to survive. Since the prey is usually inferior to its predator, it must use wit to its advantage. When all else seems futile, thanatosis seems the only way to go.
Thanatosis – what is it?
Thanatosis, colloquially speaking, is playing dead. It is a behavior manifested by certain animals to deceive their predators. Running away could have been the best option but when cornered the animal has to make a hasty decision between fighting back and feigning death. In certain situations, thanatosis works; it proves to be more useful than battling it out in the rubble. Not only does it make the animal save up precious energy but it also buys time to figure out a route with higher chances of escape. Instead of forcing a way out, thanatosis applies trickery, i.e. by deceptively submitting to the opponent only to seize the right opportunity to escape when it comes.
Thanatosis and predation
Several animals use thanatosis to facilitate escape. For instance, a threatened Eastern hognose snake (Heterodon platirhinos) initially displays an intimidating pose. It raises its head off the ground, hiss, and strike. When the threat display fails, the snake engages its opponent to a dramatic performance of thanatosis. As if poisoned and about to die, the snake rolls onto its back, shudders, and hangs out its tongue. Not only will it look dead… it will also smell dead when it releases a foul-smelling fluid from its cloaca.1
The phrase “playing possum” stems from the thanatosis behavior of Virginia opossum (Didelphis virginiana). When it senses extreme danger, it appears dead similar to a comatose state. Out of great fear, it lies on its side with eyes and mouth open and tongue hanging out. It releases a greenish fluid that smells rotten through its anus. This trickery display causes the deterrence of predators. A prey that died suddenly seemed like something went wrong and eating it might lead to trouble.
Unfortunately, there are also predators that utilize thanatosis to deceive preys. Cichlids (Nimbochromis sp.), for instance, act dead by not moving so that an unsuspecting prey will be lured closer, and therefore get a better chance of capturing it.
Thanatosis to evade sexual cannibalism
Apart from evading a predator, certain animals use thanatosis to deceive an aggressive female to mate with. Mating in some spiders can be a dangerous activity. The female spiders attack the male spiders to feed on them after sex. This devouring of another individual of the same species before, during, or after copulation is called sexual cannibalism. While there are spiders that welcome it (read: The Amazing Spider Dads), other spiders attempt to circumvent it. For instance, the male wolf spiders perform thanatosis to avoid ending up as a meal after copulating.2 The male nursery web spiders (Pisaura mirabilis) also resort to thanatosis but apart from it they also do nuptial gift-giving during courtship rituals. In a study by Hansen et al.3, the male spiders that played dead had more success in mating with hostile females and stayed alive right after.
In the wild, resorting to thanatosis to survive is not uncommon. At the edge of demise, these animals enact the greatest performance of their lives. They appear to have died a disturbing death to mislead predators. Who prefers a spoiled meat? Most predators want their meal fresh; hence, they may no longer find a prey looking repulsive and smelling putrid appetizing. Thanatosis proves its invaluable use as an anti-predation strategy. Besides that, animals playing dead for sex and evading cannibalism demonstrate that thanatosis is tantamount to surviving — die to live!
— written by Maria Victoria Gonzaga
1 FrankSnakes. (2012). Eastern Hognose (Heterodon platirhinos) Playing Dead. Retrieved from https://www.youtube.com/watch?v=UxbT2acTsrM
2 Seriously Science. (2016). Male spiders play dead to avoid “sexual cannibalism.” Retrieved from http://blogs.discovermagazine.com/seriouslyscience/2016/05/26/5406/
3 Hansen, L.S., Gonzales, S. F., Toft, S., & Bilde, T. (2008).Thanatosis as an adaptive male mating strategy in the nuptial gift–giving spider Pisaura mirabilis. Behavioral Ecology, Volume 19, Issue 3, 1 May 2008, Pages 546–551. Retrieved from https://academic.oup.com/beheco/article/19/3/546/185057