Animal suicide

Animal suicide refers to self-destructive behavior displayed by various species of animal that becomes likened to suicide.

Self-destruction

Carpenter ants and some species of termite will rupture glands in a process called autothysis. Termites will use autothysis to defend their colony, as the ruptured gland produces a sticky secretion that leads to a tar baby effect in defense.^[1][2] When threatened by a ladybug, the pea aphid will explode itself, protecting other aphids and sometimes killing the ladybug.^[3]

Suicidal behavior

Many animals that appear to be depressed or grieving begin to exhibit self-destructive behavior that sometimes ends in death.^[3] In 1845, the Illustrated London News reported that a Newfoundland dog had been acting less lively over a period of days before being seen "to throw himself in the water and endeavor to sink by preserving perfect stillness of the legs and feet".^[3] Every time he was rescued he attempted to do this again before he finally held his head underwater until death.^[3] Other dogs, as well as ducks, have also drowned themselves.^[4] One duck did so after the death of its mate.^[5] At Overtoun Bridge in Scotland, many dogs have been known to leap to their deaths; although long reported to be suicide, many scientists have now attributed it to the smell of mink.^[6] Some dogs will refuse food after the death of their owner until they die as well.^[5] Pods of whales have repeatedly beached themselves in mass strandings.^[7][8] In 2009, 28 cows and bulls mysteriously threw themselves off an alpine cliff over the span of three days.^[9] One deer leapt from a cliff to its death so as to avoid being captured by hunting dogs.^[5] In 2005 in Turkey, 1,500 sheep walked off a cliff; some 400 died.^[10] Suicidal behavior has been observed more in female animals than male and in more vertebrates than invertebrates.^[11]

Animal suicide was long used to define human suicide; in the 1800s animal suicide was seen as an act of abuse, madness, love, or loyalty, the same acts human suicide was seen as.^[3] Although it is impossible to determine what drives animals to self-destruction, some specific traits associated with human suicide can be successfully transferred to animals.^[12] Scientists have been unable to explain whether or not animals are able to consciously end their own lives.^[11]

Suicide-inducing parasitism

Certain types of parasites will cause their hosts to commit suicidal behavior. A main example is the phylum Acanthocephala, which will direct its host to a predator so as to be eaten by the predator, their new definitive host. The parasitic worm Spinochordodes tellinii will develop in grasshoppers and crickets until it is grown, at which time it will cause its host to leap into water to its death so that the worm can reproduce in water.^[13] However, S. tellinii only causes its host to drown when the host is already close to water as opposed to seeking it out over large distances.^[14]

Infection with Toxoplasma gondii has been shown to alter the behavior of mice and rats in ways thought to increase the rodents’ chances of being preyed upon by cats.^[15][16][17] Infected rodents show a reduction in their innate aversion to cat odors; while uninfected mice and rats will generally avoid areas marked with cat urine or with cat body odor, this avoidance is reduced or eliminated in infected animals. Moreover, some evidence suggests this loss of aversion may be specific to feline odors: when given a choice between two predator odors (cat or mink), infected rodents show a significantly stronger preference to cat odors than do uninfected controls.

Misconceptions

A popular misconception is that the lemming will commit mass suicide during migration. This misconception was first popularized by media in the 1950s, such as a mention in the Cyril M. Kornbluth short story "The Marching Morons" in 1951 and the 1955 comic "The Lemming with the Locket", inspired by a 1953 American Mercury article.^[18][19] Perhaps one of the most influential factors in this misconception was the Academy Award-winning Disney film White Wilderness, which showed staged footage of lemmings jumping off a cliff during migration.^[20]

See also

• Autothysis
• Exploding animal
• Self-destruct
• Antipredator adaptation

References