Animal suicide refers to any kind of self-destructive behavior displayed by various species of non-human animals There are anecdotal reports of grieving pets displaying such behaviour after the death of their owner, or monogamous animals refusing to feed after the death of their mate.
Some parasites manipulate the behavior of their host, causing them to expose themselves to greater risks of predation to enable the parasite to proceed to the next life-cycle stage. Some carpenter ants and termites use autothysis, producing a sticky secretion to trap colony marauders, and pea aphids will sometimes explode, protecting other pea aphids from ladybugs.
Suicidal behavior
It is generally considered that humans are the only known animals to use weapons when putting an end to their own life. There are examples of non-human animals dying in defence of their family or colony, such as the case of pea aphids increasing their chances of death as a response to parasitism. Many animals that appear to be depressed or grieving begin to exhibit self-destructive behavior that sometimes ends in death. 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". Every time he was rescued he attempted to do this again before he finally held his head underwater until death. Other dogs, as well as ducks, have also drowned themselves. One duck did so after the death of its mate. 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. Some dogs will refuse food after the death of their owner until they die as well. In 2009, 28 cows and bulls mysteriously threw themselves off a cliff in the Swiss Alps over the span of three days. One deer leapt from a cliff to its death so as to avoid being captured by hunting dogs. Another famous example of animal suicide is the case of the dolphin which most often portrayed Flipper, on the 1960s television show Flipper. According to trainer Richard O' Barry in the film The Cove, Kathy, the dolphin, drowned itself before him. Suicidal behavior has been observed more in female animals than male and in more vertebrates than invertebrates.
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. 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. Scientists have been unable to explain whether animals are able to consciously end their own lives.
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. When threatened by a ladybug, the pea aphid will explode itself, protecting other aphids and sometimes killing the ladybug. Another example is the Camponotus saundersi, or Malaysian worker ant, which is capable of committing suicide by exploding.
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. 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.
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. 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.
Suicide induction in intermediate hosts has been shown to help disperse the parasites to their final hosts. The intermediate host of Parvatrema affinis is the bivalve mollusc, "Macoma balthica". The clam feed when in the sublittoral and tidal flat muds, and usually leave no conspicuous marks in the mud that could indicate their presence. However, infected clams are concentrated in the higher parts of the tidal flats, closer to shore, and leave conspicuous zig-zag markings in the sand. Visual and tactile cues have shown to be used by oyster catchers and other shore birds, the definitive hosts of the parasite.
Misconceptions
A popular misconception is that the lemming will commit mass suicide during migration. This misconception was first popularized by media in the 1960s, 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. 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.
See also
- Self-destruction
- Antipredator adaptation