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Wars or conflicts can break out between different groups in some ant species for a variety of reasons. These violent confrontations typically involve entire colonies, sometimes allied with each other, and can end in a stalemate, the complete destruction of one of the belligerents, the migration of one of the groups, or, in some cases, the establishment of cordial relations between the different combatants or the adoption of members of the losing group. For some species of ants, this is even a deliberately undertaken strategy, as they require capturing pupae from other species to ensure the continuity of their colony. Thus, there are specific biological evolutions in certain species intended to give them an advantage in such conflicts. In some of these confrontations, ants can adopt ritualized behavior, even governed by certain implicit rules, for example by organizing duels between the most important ants of each colony or choosing a specific location for a battle.

These conflicts are not simply internal to ants, which can fight each other even within the same species, but also involve other animals, particularly other eusocial insects like termites or wasps. In the early 21st century, with the rapid spread of many species into new habitats facilitated by human colonization, significant wars are being waged between different supercolonies.

Terminology

The use of the term "war", found in scientific literature, is an anthropocentric analogy, derived from human wars.

Causes and prevalence

Causes

The reasons that can lead ant colonies to clash are varied and depend on the species, locations, and contexts. For a number of them, such as leafcutter ants Atta laevigata, wood ants of the genus Formica, certain species of the genus Carebara, or giant ants Dinomyrmex gigas, it is a matter of territory covered and thus the available food for the different colonies. It can also be related to issues of overpopulation of the same species in the same area at certain times of the year. In other cases, some species aim to capture the pupae of an opposing group to use them in their own colony later.

Prevalence

It is difficult to assess the prevalence of this type of behavior in ants, given the significant diversity of species, behaviors, and different situations. Some species undergo specific evolutions with the sole purpose of engaging in these conflicts, such as Polyergus rufescens, which have sickle-shaped mandibles. The emergence of supercolonies from the 19th century, facilitated by human movements, has certainly reinforced these behaviors in the affected ants. It also seems to depend on the context in which the ants find themselves. For instance, within the same species, a colony facing external threats from another ant colony can produce up to twice as many soldier larvae as a colony not experiencing the same pressures. Some species are almost exclusively on defensive strategies, such as Camponotus ligniperdus, which are peaceful and occupy a small territory but defend it fiercely against any incursion, even against more dangerous or deadly species.

Process and outcomes

Process

In general, there are two main ways ants conduct these conflicts. On the one hand, some species use specific ants that are more powerful and whose primary function is to fight. On the other hand, colonies increase the number of available fighters and send large numbers of individuals into battle. In some species, conflict is ritualized, for example through limited duels undertaken by the individuals most capable of combat, but phenomena of battles are also common. In the genus Formica, such battles are commonplace and can involve tens of thousands of individuals, and they are sometimes ritualized, with the respective groups withdrawing at nightfall only to return the next day to the same locations to resume the battle. The bodies of dead or injured ants are then brought back to the colony, where they are eaten. In other species, such as within the genus Carebara, ants arrange themselves in specific formations before the battle, like phalanxes, and advance against each other. They also regularly sacrifice workers, whose role is to try to hinder, injure, and attack enemy majors, before their own majors join the battlefield and can intervene.

In other cases, particularly among ants that aim to capture larvae or pupae, colonies use chemical weapons, such as olfactory propaganda, to try to enter the targeted colonies as discreetly as possible.

Outcomes

Generally, wars between ants are costly for the groups, which must allocate a significant portion of their production to the war effort, to the detriment of forming workers, for example. These wars can result in the death of tens of thousands of individuals within a few hours; for wood ants of the genus Formica, there are regularly 10,000 casualties per day during the spring. For these ants, the war ends either when the opposing colony is destroyed or when the available prey is sufficient again for the needs of the colonies, which have then lost thousands of members. Estimates from 2016 on certain ant species show a loss of about a third of the total colony population in case of victory.

For some species, such as Crematogaster mimosae, victory over an opposing colony usually results in the flight or death of the opposing queen, but the victorious colony often adopts the surviving ants of the losing colony, likely a way to avoid and mitigate the significant resource loss due to the war effort. In a few rare cases, the queen of the losing colony is herself adopted by the victorious colony, and the two merge.

Supercolonies

With the development of ant supercolonies, which follows human expansion into new areas, groups of dozens, hundreds, or even thousands of colonies engage in large-scale conflicts against other species. For example, around San Diego in the 2010s, millions of ants died each month in significant battles between the supercolony formed by Argentine ants and three other supercolonies present in the area.

References

1. On the idea that ants may be capable of acting according to rules, see Giuseppe Lorini, Donato A. Grasso, Andrea Loi (2024) https://doi.org/10.1163/1568539X-bja10265
2. ^ Chauvin, Rémy (1974). "Les sociétés les plus complexes chez les insectes". Communications. 22 (1): 63–71. doi:10.3406/comm.1974.1338. Archived from the original on 9 March 2024. Retrieved 8 July 2024.
3. ^ Pfeiffer, Martin; Linsenmair, Karl Eduard (1 December 2001). "Territoriality in the Malaysian giant ant Camponotus gigas (Hymenoptera/Formicidae)". Journal of Ethology. 19 (2): 75–85. doi:10.1007/s101640170002. ISSN 1439-5444.
4. ^ Mabelis, A. A. (1 January 1983). "Interference Between Wood Ants and Other Ant Species (Hymenoptera, Formicidae)". Netherlands Journal of Zoology. 34 (1): 1–20. doi:10.1163/002829684X00010. ISSN 1568-542X. Archived from the original on 8 March 2021. Retrieved 8 July 2024.
5. WHITEHOUSE, MARY E.A.; JAFFE, KLAUS (June 1996). "Ant wars: combat strategies, territory and nest defence in the leaf-cutting antAtta laevigata". Animal Behaviour. 51 (6): 1207–1217. doi:10.1006/anbe.1996.0126. ISSN 0003-3472. Archived from the original on 8 July 2024. Retrieved 8 July 2024.
6. ^ Moffett, Mark W. (2011). "Ants & the Art of War". Scientific American. 305 (6): 84–89. Bibcode:2011SciAm.305e..84M. doi:10.1038/scientificamerican1211-84 (inactive 1 November 2024). ISSN 0036-8733. JSTOR 26002920. PMID 22214134.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
7. Laurent Cournault. Les fourmis : une biodiversité méconnue (PDF). p. 6. Archived (PDF) from the original on 8 July 2024. Retrieved 8 July 2024.
8. ^ Keller, Laurent; Gordon, Élisabeth (2013). La vie des fourmis. Poches. Paris: O. Jacob. ISBN 978-2-7381-2968-0.
9. Czechowski, Wojciech (1 January 1988). "Inter- and intraspecific competive relations in Camponotus ligniperdus (Latr.) (Hymenoptera, Formicidae" (PDF). Annales Zoologici. Retrieved 8 July 2024.
10. ^ Lymbery, Samuel J.; Webber, Bruce L.; Didham, Raphael K. (12 September 2023). "Complex battlefields favor strong soldiers over large armies in social animal warfare". Proceedings of the National Academy of Sciences. 120 (37): e2217973120. Bibcode:2023PNAS..12017973L. doi:10.1073/pnas.2217973120. ISSN 0027-8424. PMC 10500280. PMID 37639613.
11. ^ CSIRO. "Ant wars: How native species can win the battle over invasive pests". phys.org. Archived from the original on 29 August 2023. Retrieved 8 July 2024.
12. ^ Rudolph, Kathleen P.; McEntee, Jay P. (17 December 2015). "Spoils of war and peace: enemy adoption and queen-right colony fusion follow costly intraspecific conflict in acacia ants". Behavioral Ecology. 27 (3): 793–802. doi:10.1093/beheco/arv219. ISSN 1045-2249. Archived from the original on 8 July 2024. Retrieved 8 July 2024.
13. Moffett, Mark W. (2012). "Supercolonies of billions in an invasive ant: What is a society?". Behavioral Ecology. 23 (5): 925–933. doi:10.1093/beheco/ars043. ISSN 1465-7279. Archived from the original on 24 August 2023. Retrieved 8 July 2024.

v t e Eusociality
Topics	Evolution of eusociality Presociality Social insects Agriculture Gamergate Group selection Haplodiploidy Identity in social insects Kin recognition Kin selection Polyethism Sexual selection in insects Social conflict Thelytoky War Worker policing
Groups	Hymenoptera Ant Apidae Crabronidae Halictidae Honey bee Vespidae Mammalia Blesmol Dwarf mongoose Meerkat Crustacean Synalpheus Thysanoptera Kladothrips Hemiptera Aphididae Coleoptera Austroplatypus incompertus Isoptera
In culture	Bees in mythology Coalescent
Pioneers, works	Karl von Frisch The Dancing Bees 1927 Charles Duncan Michener The Bees of the World 2000 Bert Hölldobler E. O. Wilson Sociobiology: The New Synthesis 1975 The Ants 1990 Journey to the Ants 1994

• War
• Dispute resolution
• Military ethics
• Violence
• Conflicts
• Ants
• Symbiosis
• Ethology
• Behavior