Animal suicide is when an animal intentionally ends its own life through its actions.[1] It implies a wide range of higher cognitive capacities that experts have been wary to ascribe to nonhuman animals such as a concept of self, death, and future intention. There is currently not enough empirical data on the subject for there to be a consensus among experts.[2] For these reasons, the occurrence of animal suicide is controversial among academics.[3]

While it has not been proven that non-human animals do, or even can, die by suicide, many animals behave in ways that may seem suicidal. There are anecdotes of animals refusing to eat in periods of grief or stress.[4][5] Some social insects have been known to defend their colony by sacrificing themselves.[6] Other animals are victims of parasites that are known to alter the behavior of their host to complete their lifecycle, which result in the host's death.[7]

Characteristics

There are yet to be definitive, unanimously agreed upon, instances of non-human animal suicide. This is due to the many components of suicide which are difficult to empirically observe without interpretation bias.[3] An animal would need to be aware of its own existence as distinct from other individuals. It would need to have an understanding of mortality and sufficient for it to realize that it is a possibility. To choose death for itself, the animal has to know about itself and that it can die. It would also need some concept of the future in order to intend to die. Each of these requisites have been studied independently, and there is some evidence of some animals being capable of each. The mirror test is currently used to determine whether an animal has a concept of self. Some animals, such as some species of cetaceans and primates, are believed to grasp the concept of death enough to mourn conspecifics.[8]

Some animals, such as octopuses, stop eating food and waste away after reproducing, seemingly losing any desire to live. As this is a genetically programmed behavior that all individuals of the species engage in, it is not intentional and therefore cannot be considered suicide.

Animal model of suicide

Several risk-factors for suicide, such as addiction, depression, and PTSD, have already been modeled independently in animals.[9][10] These animal models allow scientists to study the neuroscience behind these disorders as well as explore potential treatments. While demonstrating animal suicide itself in a lab is believed to be possible by some,[11] the ethics of driving an animal to kill itself are debated.[10][12] In the field, it can be difficult to not only find examples of suicide, but to be certain that the death was intentional, not accidental.

Suicidal behavior

Many animals that appear to be depressed or grieving begin to exhibit self-destructive behavior that sometimes ends in death, but this is not considered suicide, as the achieving of death was not necessarily the purpose or objective of the behaviors.[13]

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".[14] Every time he was rescued he attempted to do this again before he finally held his head underwater until death.[14] The newspaper ran stories on other dogs, as well as ducks, that had also allegedly drowned themselves, although the veracity or certainty of these cases is disputed.[15] In one of the alleged cases, one duck did so after the death of its mate.[16]

Another example of an alleged case of animal suicide is the case of the dolphin which most often portrayed Flipper on the 1960s television show Flipper. According to trainer Ric O'Barry in the film The Cove, Kathy, the dolphin, suffocated herself before him. The veracity or accuracy of this case has not been established in rigorous, scientific or objective terms.[17][18] Similarly, a male bottle nose dolphin named Peter who was a subject in a series of experiments led by John C. Lilly, a neuroscientist, and Margaret Howe Lovatt, a volunteer naturalist, apparently stopped breathing after it was moved to a lab in a different location and separated from Lovatt.[19][20]

Some dogs will refuse food from some unknown person after the death of their owner, a behavior that might lead to disease or death in severe cases.[16] The death of mourning animals is likely to be caused by depression leading to starvation or drowning, instead of the intent of suicide.

Aristotle described an unverified story involving one of the King of Scythia's horses dying by suicide after having been made to unwittingly impregnate its mother in his History of Animals.[21]

Group defense

Autothysis

Some species of social insects will die by suicide in an act of altruism through autothysis. These insects will sacrifice themselves if the colony is in danger, to alert the colony of danger, or if they become diseased they will sacrifice themselves to prevent the colony from becoming diseased.[6] Carpenter ants and some species of termite will rupture glands and expel a sticky toxic substance thought to be an aliphatic compound in a process called autothysis. Termites will use autothysis to defend their colony, as the ruptured gland produces a sticky harmful secretion that leads to a tar baby effect in defense.[22][23] When threatened by a ladybug, the pea aphid will explode itself, protecting other aphids and sometimes killing the ladybug.[14] Another example is the Camponotus saundersi, or Malaysian worker ant, which is capable of dying by suicide by exploding.[24]

Stinging

Honeybees use their stinger to deliver poisonous chemicals to their attacker, effectively both injuring the predator and killing the insect in the colony's defense.[25] This self-destructive and often altruistic defense is known as sting autonomy. The stinger is easily torn from the animal's body, allowing the hazardous stinger to be left stuck in the predator.[6] Honey bees are the only bees to die after stinging.[26]

Mal-adaptive behavior

Migration

Lemmings are known to migrate when the population in their area becomes too large for its food supply. During these migrations, some will swim to cross bodies of water, but not all of them will make it back to land alive. This unfortunate consequence of migration has sometimes been perceived as an act of mass suicide. This myth has been popularized in various media.[27]

Interference

Parasitism

Certain types of parasites will cause their hosts to engage in suicidal behavior, through altering how the intermediate host acts, but this is not considered suicide (at least not considered suicide in a psychological or ethological sense). The change in the host's actions often benefit the parasite's search for a final host.[28] 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.[29] 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.[30]

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.[31][32] 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.[33] 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.[34] The intermediate host of Parvatrema affinis is the bivalve mollusc, Macoma balthica.[35] The clams 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.

Examples

Tarsiers

One of the most clear examples of animal suicide would most likely be the suicidal behavior of tarsiers that are kept in captivity. Tarsiers are nervous and shy by nature, and do not do well in captivity. Many activities associated with captivity, such as camera flashes, being touched, and being kept in an enclosure, can stress the tarsiers. This stress can lead to sore eyes, which is an indication of a poor diet, and the lighting usually used in captivity can cause long-lasting damage to the eyes. When they feel too stressed out, they start beating their heads against hard surfaces, which leads to death.[36][37][38][39][40]

In media

A popular misconception is that the lemming will die by mass suicide during reproduction. 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.[41][42] Perhaps one of the most influential factors in this misconception was the 1958 Academy Award-winning Disney film White Wilderness, which showed staged footage of lemmings jumping off a cliff during reproduction.[43]

Werner Herzog's 2007 Academy Award-nominated documentary film Encounters at the End of the World features footage of a penguin marching away from the sea, going inland to its certain death.[44] National Geographic dubbed the penguin "suicidal".[45]

See also

References

  1. ↑ Courtet, Philippe, ed. (2016). Understanding Suicide. Cham: Springer International Publishing. doi:10.1007/978-3-319-26282-6. ISBN 978-3-319-26280-2.
  2. ↑ Peña-Guzmán, David M. (2017-01-01). "Can nonhuman animals commit suicide?". Animal Sentience. 2 (20). doi:10.51291/2377-7478.1201. ISSN 2377-7478. S2CID 56436713.
  3. 1 2 Preti, Antonio (December 2007). "Suicide among Animals: A Review of Evidence". Psychological Reports. 101 (3): 831–848. doi:10.2466/pr0.101.3.831-848. ISSN 0033-2941. PMID 18232440. S2CID 40423383.
  4. ↑ Preti, Antonio (January 2011). "Do Animals Commit Suicide? Does It Matter?". Crisis. 32 (1): 1–4. doi:10.1027/0227-5910/a000077. ISSN 0227-5910. PMID 21371964.
  5. ↑ Abnormal behavior in animals. Michael W. Fox. Philadelphia: Saunders. 1968. ISBN 0-7216-3825-2. OCLC 301659067.{{cite book}}: CS1 maint: others (link)
  6. 1 2 3 Shorter, J. R.; Rueppell, O. (February 2012). "A review on self-destructive defense behaviors in social insects". Insectes Sociaux. 59 (1): 1–10. doi:10.1007/s00040-011-0210-x. ISSN 0020-1812. S2CID 13257903.
  7. ↑ Moore, Janice (April 1984). "Altered Behavioral Responses in Intermediate Hosts -- An Acanthoceptalan Parasite Strategy". The American Naturalist. 123 (4): 572–577. doi:10.1086/284224. ISSN 0003-0147. S2CID 86700440.
  8. ↑ Reggente, Melissa A. L.; Alves, Filipe; Nicolau, Cátia; Freitas, Luís; Cagnazzi, Daniele; Baird, Robin W.; Galli, Paolo (2016-09-27). "Nurturant behavior toward dead conspecifics in free-ranging mammals: new records for odontocetes and a general review". Journal of Mammalogy. 97 (5): 1428–1434. doi:10.1093/jmammal/gyw089. ISSN 0022-2372.
  9. ↑ Malkesman, Oz; et al. (April 2009). "Animal Models of Suicide Trait-Related Behaviors". Trends in Pharmacological Sciences. 30 (4): 165–173. doi:10.1016/j.tips.2009.01.004. PMC 2788815. PMID 19269045.
  10. 1 2 Preti, Antonio (June 2011). "Animal model and neurobiology of suicide". Progress in Neuro-Psychopharmacology and Biological Psychiatry. 35 (4): 818–830. doi:10.1016/j.pnpbp.2010.10.027. PMID 21354241. S2CID 3459576.
  11. ↑ Lester, David (2017-01-01). "Non-human animal suicide could be tested". Animal Sentience. 2 (20). doi:10.51291/2377-7478.1286. ISSN 2377-7478.
  12. ↑ Comai, Stefano; Gobbi, Gabriella (2016), Courtet, Philippe (ed.), "Translational Research in Suicide: Is It Possible to Study Suicide in Animal Models?", Understanding Suicide, Cham: Springer International Publishing, pp. 177–188, doi:10.1007/978-3-319-26282-6_14, ISBN 978-3-319-26280-2, retrieved 2021-10-23
  13. ↑ Melissa Hogenboom. "Many-animals-seem-to-kill-themselves-but-it-is-not-suicide". BBC.Or see: http://www.bbc.com/earth/story/20160705-many-animals-seem-to-kill-themselves-but-it-is-not-suicide
  14. 1 2 3 O'Hanlon, Larry (10 March 2010). "Animal Suicide Sheds Light on Human Behavior". Discovery News. Archived from the original on 26 March 2015. Retrieved 16 August 2013.
  15. ↑ Maudsley, Henry (July 1879). "Alleged Suicide of a Dog". Mind. 4 (15): 410–413.
  16. 1 2 Palmer, Brian (16 November 2011). "Hairy-Kiri: Do animals commit suicide". Slate. Retrieved 16 August 2013.
  17. ↑ Nobel, Justin (2010-03-19). "Do Animals Commit Suicide? A Scientific Debate". Time. ISSN 0040-781X. Retrieved 2017-01-26.
  18. ↑ Peña-Guzmán, David (2017-01-01). "Can nonhuman animals commit suicide?". Animal Sentience. 2 (20). doi:10.51291/2377-7478.1201. ISSN 2377-7478.
  19. ↑ Riley, Christopher (2014-06-08). "The dolphin who loved me: the Nasa-funded project that went wrong". The Observer. ISSN 0029-7712. Retrieved 2020-11-04.
  20. ↑ "The Girl Who Talked to Dolphins". BBC Four. Retrieved 2018-04-16.
  21. ↑ History of Animals, Book 9, Chapter 34 (page 274).
  22. ↑ Maschwitz, Ulrich; Maschwitz, Eleonore (1974). "Platzende Arbeiterinnen: Eine neue Art der Feindabwehr bei sozialen Hautflüglern". Oecologia (in German). 14 (3): 289–294. Bibcode:1974Oecol..14..289M. doi:10.1007/BF01039798. PMID 28308625. S2CID 23644298.
  23. ↑ C. Bordereau; A. Robert; V. Van Tuyen; A. Peppuy (1997). "Suicidal defensive behavior by frontal gland dehiscence in Globitermes sulphureus Haviland soldiers (Isoptera)". Insectes Sociaux. 44 (3): 289–297. doi:10.1007/s000400050049. S2CID 19770804.
  24. ↑ Jones, T. H.; Clark, D. A.; Edwards, A. A.; Davidson, D. W.; Spande, T. F.; Snelling, R. R. (2004). "The Chemistry of Exploding Ants, Camponotus SPP. (Cylindricus COMPLEX)". Journal of Chemical Ecology. 30 (8): 1479–1492. Bibcode:2004JCEco..30.1479J. doi:10.1023/B:JOEC.0000042063.01424.28. ISSN 0098-0331. PMID 15537154. S2CID 23756265.
  25. ↑ Hermann, Henry R. (June 1971). "Sting autotomy, a defensive mechanism in certain social Hymenoptera". Insectes Sociaux. 18 (2): 111–120. doi:10.1007/bf02223116. ISSN 0020-1812. S2CID 42293043.
  26. ↑ Urban Bee Gardens Archived 2010-05-01 at the Wayback Machine Urban Bee Legends – by Jaime Pawelek
  27. ↑ Clough, Garrett C. (1965). "Lemmings and Population Problems". American Scientist. 53 (2): 199–212. ISSN 0003-0996. JSTOR 27836007.
  28. ↑ Moore, Janice (April 1984). "Altered Behavioral Responses in Intermediate Hosts – An Acanthoceptalan Parasite Strategy". The American Naturalist. 123 (4): 572–577. doi:10.1086/284224. ISSN 0003-0147. S2CID 86700440.
  29. ↑ Shaoni Bhattacharya (August 31, 2005). "Parasites brainwash grasshoppers into death dive". New Scientist.
  30. ↑ F. Thomas; A. Schmidt-Rhaesa; G. Martin; C. Manu; P. Durand; F. Renaud (May 2002). "Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts?". Journal of Evolutionary Biology. 15 (3): 356–361. CiteSeerX 10.1.1.485.9002. doi:10.1046/j.1420-9101.2002.00410.x. S2CID 86278524.
  31. ↑ Webster, JP; McConkey, GA (June 2010). "Toxoplasma gondii-altered host behaviour: clues as to mechanism of action". Folia Parasitologica. 57 (2): 95–104. doi:10.14411/fp.2010.012. PMID 20608471.
  32. ↑ Webster, J. P. (2007). "The Effect of Toxoplasma gondii on Animal Behavior: Playing Cat and Mouse". Schizophrenia Bulletin. 33 (3): 752–756. doi:10.1093/schbul/sbl073. PMC 2526137. PMID 17218613.
  33. ↑ Berdoy, M.; Webster, J. P.; Macdonald, D. W. (2000). "Fatal Attraction in Rats Infected with Toxoplasma gondii". Proceedings: Biological Sciences. 267 (1452): 1591–1594. doi:10.1098/rspb.2000.1182. ISSN 0962-8452. JSTOR 2665707. PMC 1690701. PMID 11007336.
  34. ↑ Trail, Deborah R. Smith (1980). "Behavioral Interactions between Parasites and Hosts: Host Suicide and the Evolution of Complex Life Cycles". The American Naturalist. 116: 77–91. doi:10.1086/283612. hdl:1808/17548. S2CID 16777324.
  35. ↑ Swennen, Ching (1974). "Observations on the trematode parvatrema affinis, causative agent of crawling tracks of macoma balthica". Netherlands Journal of Sea Research. 8 (1): 108–115. Bibcode:1974NJSR....8..108S. doi:10.1016/0077-7579(74)90029-5.
  36. ↑ "18 Facts About The Tarsier: Suicidal Monkey of Philippines!". Man vs Clock. 14 December 2022. Retrieved 18 June 2023.
  37. ↑ Bales, Bob (11 November 2022). "The Heartbreaking Story Of The Philippine Tarsier Of Bohol: And Why They Commit Suicide". The Traveling Fool. Retrieved 18 June 2023.
  38. ↑ "Spectral Tarsier – Why are Tarsiers Suicidal?". Primates Park. 20 March 2022. Retrieved 18 June 2023.
  39. ↑ Mudditt, Jessica (16 April 2018). "Inside the Mystery of Animal 'Suicide'". VICE. Retrieved 18 June 2023.
  40. ↑ "Philippine Tarsiers, the Suicidal Primates". Treehugger. 7 March 2012. Retrieved 18 June 2023.
  41. ↑ Lederer, Muriel. "Return of the Pied Piper". The American Mercury, Dec. 1953, pp. 33–4.
  42. ↑ Blum, Geoffrey. 1996. "One Billion of Something", in: Uncle Scrooge Adventures by Carl Barks, #9.
  43. ↑ "Did Disney Fake Lemming Deaths for the Nature Documentary 'White Wilderness'?". Snopes.com. 27 February 1996.
  44. ↑ Cooke, Tim (25 April 2017). "What does Werner Herzog's nihilist penguin teach us about life?". Little White Lies. Retrieved 28 December 2022.
  45. ↑ Potts, Mary Anne (22 July 2008). "Herzogian Antarctica: Pink Floyd Seals and a Suicidal Penguin". National Geographic. Archived from the original on December 28, 2022. Retrieved 28 December 2022.

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