The survival technique of thanatosis, or in colloquial terms, “playing dead” is characterized by cessation of voluntary activity in an animal, where the said animal assumes a posture suggestive of death and decay.
The animal kingdom is full of varied astonishing and intriguing phenomena. If anyone keenly observes nature, it is very likely that he may notice and find many magnificent and strange things which might have been reported earlier or it might be brand new discoveries to the scientific domain. In our natural eco-system the most important thing which we observe and encounter everyday is the fight for food between intra and inter specific animals. Some animals like herbivores face somewhat less problems in regards to availability of sustenance, as there are plenty of plant species to fill their bellies, but the actual problem arises among the carnivores which depend upon and hunt herbivores for their food and survival. There is a continuous natural tug of war between the predator and prey to overcome or deceive one-another in order to survive. Consequently there are many survival techniques and behaviours found among prey animals which are thus mind blowing and surprising too. Playing possums or apparent death is one of the gimmicks which is displayed by the opossums to deceive and evade its predators.
An opossum is a small, cat- sized marsupial (animals which keep their immature young ones till its maturity in a pouch found in females called marsupium) found mainly in North, Central and South America. They generally grow no larger than 15 pounds. , and belong to the largest order of marsupials in the Western Hemisphere which comprises more than 103 species and 19 genera. Opossums generally originate in South and Central America, and have extended its territory in North America due to connection of the two continents. Due to their unspecialized biology, flexible diets and reproductive habits they have become successful colonizers and survivors in diverse conditions of the harsh American continents.
Resembling other marsupials like kangaroos and koalas, opossums belong to the order Didelphinomorphia, and thus have two (di) wombs. This small animal is a semi-arboreal omnivore. They have long snouts and a narrow braincase. Their incisors are very small but canines are large comparatively. Like new-world monkeys, opossums have prehensile tail which they use in for purposes like climbing, holding etc. It also helps in stability of the animal while foraging on trees. Even though opossums are opportunistic omnivores, their different species vary in the amount of meat and vegetation they include in their diet. Opossums are nocturnal animals and are useful to humans. They have a diverse diet and feed on many harmful pests – insect and small animal which tend to destroy crop.
Opossums are solitary and nomadic, and stay in one area as long as food and water are easily available. They usually prefer to avoid a fight if at all possible. As nocturnal animal they prefer dark and secure areas. They move slowly on the ground and thus are vulnerable to predators such as dogs, coyotes and foxes.
Opossums are generally peaceful animals, hence coming across any danger than they prefer to avoid fight as much as possible. On the other hand, if cornered they will hiss, growl and even bite and try to dodge themselves away from the scene of confrontation. In fact these are their first line of defence behaviour against their likely predators. But considering the situations where is no option to escape and death is inevitable, then these animals display a unique behaviour i.e. playing dead, feigning death or playing possum. In fact, this is their unique defence tactic whenever they perceive threat. Scientifically this form of animal deception is also known as tonic immobility or thanatosis. Playing dead is an involuntary response of the opossums. The stress of the confrontation facing the opossum causes them to go into a shock like condition. It can last from 40 minutes to an hour depending upon the situation. In this state the opossum’s front feet form into a ball like position and drool runs out from its mouth. In some extreme conditions their body becomes hard to move and appear that rigor mortis has begun and in this condition they can be turned and even carried away without any reaction. In addition to this they also produce a smell of decay. From their anal glands the opossum emit green mucus like substance that discourages most of their predators from feeding upon them. This foul smell leads the predators to believe that the opossum’s body is an unpleasant rotting carcass and is unhealthy to feed on them. Thus the inert opossum leaves no stone unturned to de-excite the appetite of its predator and therefore they leave it alone to decay. However despite appearances pointing otherwise, the opossum remains partially conscious throughout tonic immobility. The animal typically regains its full-consciousness after a period of few minutes to an hour – a process that begins with slight twitching of its ear.
In the light of its unique defence behaviour opossums have opened a new dimension of scientific research. Latest researches point out that this unique behaviour of apparent death is not confined only to opossums, rather myriad of other animal species also display apparent death whenever they perceive or sense a mark of danger or threat. For instance in various species of sharks such as Lemon shark, Reef sharks and Tiger sharks, apparent death or tonic immobility can be induced just by placing a hand lightly on the side of animals snout in the area surrounding the eyes. It has been observed that Orcas exploits sharks’ tonic immobility to prey on them. The hog-nosed snake found in the American continent displays another interesting example of apparent death. Whenever this snake senses an unwelcome condition than a threatened snake rolls into their back and appears to be dead dissipating a foul smell added with a volatile fluid which oozes from its body. Predators then lose interest in the snake which both look and smells dead. One possible reason for predators disliking the snake is that rotten smelling animals are avoided as they are potential candidate of any infectious disease. Apart from these there are other animals like Goldfish, Cichlids etc which remain into a quiescent state, unresponsive and motionless for a considerable period of time when sensing danger. It is not denying the fact that this apparent death tactic of opossum has influenced both the common resident and scientific community profoundly. Perhaps this is the reason that in English language, the phrasal idiom “Playing Possum” is formulated to describe humans who use this same method to avoid any danger or confrontational situations of their own.