Tango (from the Greek thánatos“death”), pretend to be dead Staying completely immobile, it is a fairly widespread behavior among animals, which put it in place as defensive behavior when they are touched by a potential predator, or in one dangerous situation. The most famous example, to the point of becoming proverbial, comes fromopossumspecifically the Opossum of Virginia (Didelphis Virginiana). When he feels threatened, this marsupial pretends to be dead: he spreads to the side by stiffening himself, lines the tongue out of his mouth and secretes a foul -smelling liquid of the anus. Even if the majority of animals prefers to flee, tanitosis can offer a last chance to distract or confuse the predator when the animal feels put on the tightening. From opossum to snakes, from spiders to fish, it is a strategy for mainly defensivebut which is also used by some predators or for reproductive purposes.
Which animals pretend to be dead and the evolutionary origins of tanitosis
Tangosi is found in more disparate animals: mammals, reptiles (snakes), amphibians (frogs), birds, fish and numerous invertebrates. It is a behavior in particular not strictly related among them, and for this reason an example of convergent evolution: this behavior did not emerge in a single species and then went to its ancestors, but instead it emerged several times in a manner independent during the evolutionary history of different species.
For this reason, the advantages for survival hypothesized by evolutionist scholars are the most disparate: from defensive and predatory strategies, to the reproductive ones, such as some species of spiders, and it is possible that tanitous increases the survival of individuals of species that live in colonies or numerous groups. Many predators, in fact, faced with the choice of chasing active prey or those who pretend to be death, tend to focus on the first: whoever pretends to be dead thus have the selfish opportunity to Attract less attention and exploit the distraction offered by his escape companions to save himself calmly, as soon as the danger moves away.
Defensive tanitosis
The most common tanitosis in the animal world is of the “defensive” type, that is, the one used by the prey that are attached or perceive imminent threat. This must be distinguished from the behavior of “freezing”, or immobilization, used by both predators and prey not to be noticed. The sight of many animals is very susceptible to movements and, remaining immobile when you are lurking or when you perceive something suspicious, animals increase their survival chances trying to get noticed as little as possible.
Tango, on the other hand, is a state of tonic immobility and comes when you are instead certain to have been seen. Animal animals pretend to be dead and the lie can be very convincing. In the opossum, for example, the frequency of the heartbeat and breathing are reduced by 46% and 31% respectively, becoming more difficult to perceive, and the body temperature drops by 0.6 degrees, replicating the cooling of a dead body recently.
In most cases there is a muscle stiffeningwhich simulates the rigor mortis of the corpses: the animal, even if it continues to observe the surrounding environment, remains rigid and immobile even if touched or handled by a predator. In the opossum this pseudo-city self-induced state It can last even 4 hours, but the animal remains conscious during the duration and can quickly return to an aggressive and reactive state.
To make deception even more convincing, some animals expel feces and vomiting that replicate the smell of decompositionlike the Porco muzzle snake (Herodon Nasicus) which can even issue blood from the mouth. The advantage of pretending to be dead and decomposed comes from the fact that instinctively many species do not consume corpses, for fear of diseases, and thus lose interest. Even once captured, tangosi can offer a last one escape opportunities: believing that his prey is dead and no longer able to react, a predator can lower his guard and give up the grip for an instant, when enough to the animal to escape away from his clutches.
Tanquiosi as a predatory strategy
The use of the predators is much rarer to the use of the predators. At the foxes, perhaps because of their reputation as a shrewd predator, for example the tactic is attributed to pretend to be died to attract the crows, and then attack them as soon as they approach. However, Solid scientific evidence is missing on the actual occurrence of this behavior.
The only proven observation of tanitosi in predators for attract saprophagi animals (that is, that they feed on corpses) We find it in some cycle species, a family of fresh water fish from African and South American lakes. The fish set up on the side on the sandy bottom of the lake and change the coloring of their skin, making it more discolored and slumped. Small saprophages like other fish or invertebrates, attracted by the carcass, approach and end up being eaten by the cyclid, which attacks them quickly as soon as they are at reach.
