{{Short description|Over 50 species of leaf-foraging ants of the Americas}} [[File:Atta cephalotes-pjt.jpg|thumb|upright=1.15|''Atta cephalotes'', Wilhelma Zoo, Stuttgart]]
'''Leafcutter ants''' are fungus-growing ants that share the behaviour of cutting leaves which they carry back to their nests to farm fungus. Next to humans, leafcutter ants form some of the largest and most complex animal societies on Earth. In a few years, the central mound of their underground nests can grow to more than {{convert|30|m|ft|abbr=on}} across, with smaller radiating mounds extending out to a radius of {{convert|80|m|ft|abbr=on}}, taking up {{convert|30|to|600|m2|sqft|abbr=on}} and occupied by 3.55 million individuals.<!--<ref name="Ross-11"/>-->
== Leafcutting groups ==
Leafcutter ants are any of at least 55 species<ref name="antwiki-acromyrmex">{{cite web |last1=Shattuck |first1=Steven O. |title=''Acromyrmex'' |url=https://antwiki.org/wiki/Acromyrmex |website=AntWiki |publisher=antwiki.org |access-date=15 October 2024 |ref=antwiki-acromyrmex}}</ref><ref name="antwiki-atta">{{cite web |last1=Shattuck |first1=Steven O. |title=''Atta'' |url=https://antwiki.org/wiki/Atta |website=AntWiki |publisher=antwiki.org |access-date=15 October 2024 |ref=antwiki-atta}}</ref><ref name="antwiki-amoimyrmex">{{cite web |last1=Shattuck |first1=Steven O. |title=''Amoimyrmex'' |url=https://antwiki.org/wiki/Amoimyrmex |website=AntWiki |publisher=antwiki.org |access-date=15 October 2024 |ref=antwiki-amoimyrmex}}</ref> of leaf-chewing ants belonging to the three genera ''Atta'', ''Acromyrmex'', and ''Amoimyrmex'', within the tribe Attini.<ref name="cristianoetal2020">{{cite journal |last1=Cristiano |first1=Maykon Passos |last2=Cardoso |first2=Danon Clemes |last3=Sandoval-Gómez |first3=Vivian E. |last4=Simões-Gomes |first4=Flávia Carolina |display-authors=1 |title=''Amoimyrmex'' Cristiano, Cardoso & Sandoval, gen. nov. (Hymenoptera: Formicidae): a new genus of leaf-cutting ants revealed by multilocus molecular phylogenetic and morphological analyses |journal=Austral Entomology |date=5 December 2020 |volume=59 |issue=4 |pages=643–644 |doi=10.1111/aen.12493 |url=https://onlinelibrary.wiley.com/doi/full/10.1111/aen.12493 |access-date=15 October 2024 |ref=cristianoetal2020|url-access=subscription }}</ref> These species of tropical, fungus-growing ants are all endemic to South and Central America, Mexico, and parts of the southern United States.<ref name="Ross-11">{{Harvnb|Piper|2007|pp=11–13}}.</ref> Leafcutter ants can carry up to 50 times their body weight<ref>{{Cite web |title=9 Facts About Leafcutter Ants |url=https://www.treehugger.com/crazy-facts-leaf-cutter-ants-4864484 |access-date=2025-05-08 |website=Treehugger |language=en}}</ref> and cut and process fresh vegetation (leaves, flowers, and grasses) to serve as the nutritional substrate for their fungal cultivates.<ref name="SchultzBrady2008">{{cite journal |title=Major evolutionary transitions in ant agriculture |journal=Proceedings of the National Academy of Sciences of the United States of America |last1=Schultz |first1=T. R.|first2=S. G. |last2=Brady |year=2008 |volume=105 |issue=14 |doi=10.1073/pnas.0711024105 |pages=5435–5440 |pmid=18362345 |pmc=2291119 |bibcode=2008PNAS..105.5435S |doi-access=free}}</ref> The leaf cutter ant species has a bite force of 800 mN, which is 2600 times their body weight, which allows them to cut leaves as well as defend the nest.<ref>{{Cite journal |last1=Püffel |first1=Frederik |last2=Roces |first2=Flavio |last3=Labonte |first3=David |date=2023-07-01 |title=Strong positive allometry of bite force in leaf-cutter ants increases the range of cuttable plant tissues |journal=The Journal of Experimental Biology |volume=226 |issue=13 |pages=jeb245140 |doi=10.1242/jeb.245140 |issn=1477-9145 |pmc=10357016 |pmid=37293932 |bibcode=2023JExpB.226B5140P }}</ref>
''Acromyrmex'' and ''Atta'' ants have much in common anatomically; however, the two can be identified by their external differences. ''Atta'' ants have three pairs of spines and a smooth exoskeleton on the upper surface of the thorax, while ''Acromyrmex'' ants have four pairs and a rough exoskeleton.<ref>{{Cite web |url=http://www.cs.unc.edu/~hedlund/dev/ants/GenusDiag/GenusDiag.html |title=Diagnoses of the North American: Ant Genera (Hymenoptera: Formicidae) |date=March 2005 |first=Kye S. |last=Hedlund |archive-date=August 24, 2007 |archive-url=https://web.archive.org/web/20070824104128/http://www.cs.unc.edu/~hedlund/dev/ants/GenusDiag/GenusDiag.html }}</ref> The exoskeleton itself is covered in a thin layer of mineral coating, composed of rhombohedral crystals that are generated by the ants.<ref>{{Citation |last1=Li|first1=Hongjie |name-list-style=amp |last2=Sun |first2=Chang-yu |year=2020 |title=Biomineral armor in leaf-cutter ants |journal=Nature Communications|volume=11 |issue=11 |page=5792 |doi=10.1038/s41467-020-19566-3 |pmid=33235196 |pmc=7686325 |doi-access=free |bibcode=2020NatCo..11.5792L }}.</ref> ''Amoimyrmex'' and ''Acromyrmex'' differ in that ''Amoimyrmex'' lacks tubercles on the first gastral segment, and recent phylogenetic evidence shows that ''Amoimyrmex'' diverged before the other two genera of leafcutter ants.<ref name="cristianoetal2020"/>
== Colony lifecycle ==
=== Reproduction and colony founding ===
[[File:Atta_colombica_queen.jpg|thumb|''Atta colombica'', queen with larvae and workers on substrate]]
Winged females and males leave their respective nests ''en masse'' and engage in a nuptial flight known as the ''revoada'' (Portuguese) or ''vuelo nupcial'' (Spanish). Each female mates with multiple males to collect the 300 million sperm she needs to set up a colony.<ref name="Extraordinary_Animals" >{{citation |title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals |first=Ross |last=Piper |year=2007 |page=[https://archive.org/details/extraordinaryani0000pipe/page/298 298] |isbn=978-0-313-33922-6 |publisher=Greenwood Press |url=https://archive.org/details/extraordinaryani0000pipe/page/298 }}.</ref>
Once on the ground, the female loses her wings and searches for a suitable underground lair in which to found her colony. The success rate of these young queens is very low, and only 2.5% will go on to establish a long-lived colony. To start her own fungus garden, the queen stores bits of the parental fungus garden mycelium in her infrabuccal pocket, which is located within her oral cavity.<ref name="Gardening_Ants,_The_Attines" >{{citation |title=Gardening Ants, The Attines |first=Neal A. |last=Weber |year=1972 |pages=[https://archive.org/details/gardeningantsatt0000webe/page/14 14, 34] |isbn=978-0-87169-092-0 |publisher=The American Philosophical Society |url-access=registration |url=https://archive.org/details/gardeningantsatt0000webe/page/14 }}.</ref> Colonies are generally founded by individual queens — haplometrosis.<ref name="Lofgren-Meer-2018">{{cite book | editor-last1=Lofgren | editor-first1=Clifford | editor-first2=Robert K. Vander | editor-last2=Meer | title=Fire Ants and Leaf-cutting Ants : Biology and Management | publisher=Routledge | publication-place=New York, NY | year=2018 | isbn=978-0-429-03826-6 | oclc=1090012991 | pages=xv+435}}</ref>{{rp|125}} Because colonies with multiple queens over the lifespan of the colony have been found by a large number of investigators {{endash}} by Weber (1937), Jonkman (1977), Huber (1907), Moser & Lewis (1981), Mariconi & Zamith (1963), Moser (1963), and Walter et al. (1938) — it is believable that some colonies have multiple foundresses — termed pleometrosis.<ref name="Lofgren-Meer-2018" />{{rp|125}} Colony founding by pleometrosis has only been confirmed in ''Atta texana,'' by Vinson (1985).<ref name="Lofgren-Meer-2018"/>{{rp|125}}
=== Colony hierarchy ===
In leafcutter colonies, ants are divided into castes, based mostly on size, that perform different functions. ''Acromyrmex'' and ''Atta'' exhibit a high degree of polymorphism, four castes being present in established colonies — minims, minors, mediae, and majors. Majors are also known as soldiers or dinergates. ''Atta'' ants are more polymorphic than ''Acromyrmex'', meaning comparatively less difference occurs in size from the smallest to largest types of ''Acromyrmex''.{{cn|date=October 2024}}
[[File:leaf cutter ants arp.jpg|thumb|right|Leafcutter ant ''Atta cephalotes'']]
* Minims are the smallest and skinniest workers, and tend to the growing brood or care for the fungus gardens. Head width is less than 1 mm. * Minors are slightly larger than minim workers, and are present in large numbers in and around foraging columns. These ants are the first line of defense and continuously patrol the surrounding terrain and vigorously attack any enemies that threaten the foraging lines. Head width is around 1.8–2.2 mm. * Mediae are the generalized foragers, which cut leaves and bring the leaf fragments back to the nest. * Majors, the largest worker ants, act as soldiers, defending the nest from intruders, although recent evidence indicates majors participate in other activities, such as clearing the main foraging trails of large debris and carrying bulky items back to the nest. The largest soldiers (''Atta laevigata'') may have total body lengths up to 16 mm and head widths of 7 mm.{{cn|date=October 2024}}
== Ant–fungus mutualism ==
Their societies are based on an ant–fungus mutualism, and different species of ants use different species of fungus, but all of the fungi the ants use are members of the family Lepiotaceae. The ants actively cultivate their fungus, feeding it with freshly cut plant material and keeping it free from pests and molds. This mutualistic relationship is further augmented by another symbiotic partner, a bacterium that grows on the ants and secretes chemicals; essentially, the ants use portable antimicrobials. Leaf cutter ants are sensitive enough to adapt to the fungi's reaction to different plant material, apparently detecting chemical signals from the fungus. If a particular type of leaf is toxic to the fungus, the colony will no longer collect it. The only two other groups of insects to use fungus-based agriculture are ambrosia beetles and termites. The fungus cultivated by the adults is used to feed the ant larvae, and the adult ants feed on leaf sap. The fungus needs the ants to stay alive, and the larvae need the fungus to stay alive, so mutualism is obligatory.
The fungi used by the higher attine ants no longer produce spores. These ants fully domesticated their fungal partner 15 million years ago, a process that took 30 million years to complete.<ref>{{Cite web |last=Institution |first=Smithsonian |title=Crop Domestication Is a Balancing Act |url=https://www.si.edu/newsdesk/releases/crop-domestication-balancing-act |access-date=2024-09-29 |website=Smithsonian Institution |language=en}}</ref> Their fungi produce nutritious and swollen hyphal tips (gongylidia) that grow in bundles called staphylae, to specifically feed the ants.<ref>{{Cite news |last=Wade |first=Nicholas |date=1999-08-03 |title=For leaf-cutter ants, farm life isn't so simple |url=https://www.nytimes.com/1999/08/03/science/for-leaf-cutter-ants-farm-life-isn-t-so-simple.html?pagewanted=all |work=The New York Times}}</ref> ''Leucoagaricus gongylophorus'' is the most commonly documented fungi farmed by higher attine ant species.<ref>{{Cite journal |last1=Pathak |first1=Ayush |last2=Kett |first2=Steve |last3=Marvasi |first3=Massimiliano |date=2019-09-26 |title=Resisting Antimicrobial Resistance: Lessons from Fungus Farming Ants |url=https://linkinghub.elsevier.com/retrieve/pii/S0169534719302563 |journal=Trends in Ecology & Evolution |language=en |volume=34 |issue=11 |pages=974–976 |doi=10.1016/j.tree.2019.08.007|pmid=31564381 |bibcode=2019TEcoE..34..974P |url-access=subscription }}</ref><ref>{{Citation |last1=Benjamin |first1=Richard K. |date=2004-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780125095518500210 |work=Biodiversity of Fungi |pages=395–433 |editor-last=Mueller |editor-first=Gregory M. |place=Burlington |publisher=Academic Press |doi=10.1016/b978-012509551-8/50021-0 |isbn=978-0-12-509551-8 |access-date=2022-07-08 |last2=Blackwell |first2=Meredith |last3=Chapela |first3=Ignacio H. |last4=Humber |first4=Richard A. |last5=Jones |first5=KEVIN G. |last6=Klepzig |first6=Kier D. |last7=Lichtwardt |first7=Robert W. |last8=Malloch |first8=David |last9=Noda |first9=Hiroaki |title=Insect- and Other Arthropod-Associated Fungi |editor2-last=Bills |editor2-first=GERALD F. |editor3-last=Foster |editor3-first=Mercedes S.|url-access=subscription }}</ref>
== Behaviour ==
thumb|Workers of ''Atta colombica'' at work
thumb|Leafcutter ant in Costa Rica
Leafcutter ants have very specific roles in taking care of the fungal garden and dumping the refuse. Waste management is a key role for each colony's longevity. The necrotrophic parasitic fungus ''Escovopsis'' threatens the ants' food source and thus is a constant danger to the ants. The waste transporters and waste-heap workers are the more dispensable leafcutter ants, ensuring the more precious ants can work. The ''Atta colombica'' species, unusually for the Attine tribe, have an external waste heap. Waste transporters take the waste, which consists of used substrate and discarded fungus, to the waste heap. Once dropped off at the refuse dump, the heap workers organise the waste and constantly shuffle it around to aid decomposition. ''A. colombica'' have been observed placing dead ants around the perimeter of the waste heap.<ref>{{Citation |last1=Hart |first1=A. G. |last2=Ratnieks |first2=F. L. W. |year=2002 |title=Waste management in the leaf-cutting ant ''Atta colombica'' |journal=Behavioral Ecology |volume=13 |issue=2 |pages=224–231 |doi=10.1093/beheco/13.2.224 |doi-access=free }}.</ref><ref>{{Citation |last1=Bot |first1=A. N. M. |last2=Currie |first2=C. R. |last3=Hart |first3=A. G. |last4=Boomsma |first4=J. J. |year=2001 |title=Waste Management in Leaf-cutting Ants |journal=Ethology Ecology and Evolution |volume=13 |issue=3 |pages=225–237 |doi= 10.1080/08927014.2001.9522772|bibcode=2001EtEcE..13..225B |s2cid=18918574 }}.</ref>
In addition to feeding the fungal garden with foraged food, mainly consisting of leaves, it is protected from ''Escovopsis'' by the antibiotic secretions of Actinomycetota (genus ''Pseudonocardia''). This mutualistic micro-organism lives in the metapleural glands of the ant.<ref>{{Citation |last1=Zhang |first1=M. M. |last2=Poulsen |first2=M. |name-list-style=amp |last3=Currie |first3=C. R. |year=2007 |title=Symbiont recognition of mutualistic bacteria by Acromyrmex leaf-cutting ants |journal=The ISME Journal |volume=1 |issue=4 |pages=313–320 |doi=10.1038/ismej.2007.41 |pmid=18043642 |doi-access=free |bibcode=2007ISMEJ...1..313Z }}.</ref> Actinomycetota are responsible for producing the majority of the world's antibiotics today.
Leafcutter ants use chemical communication and stridulation (substrate-borne vibrations) to communicate with each other.<ref>{{Cite journal|last1=Hager|first1=Felix A.|last2=Kirchner|first2=Lea|last3=Kirchner|first3=Wolfgang H.|date=2017-12-15|title=Directional vibration sensing in the leafcutter ant Atta sexdens|journal=Biology Open|language=en|volume=6|issue=12|pages=1949–1952|doi=10.1242/bio.029587|issn=2046-6390|pmc=5769659|pmid=29247049}}</ref>
Leafcutter ants prefer disturbed habitats, likely due to higher concentrations of pioneer plant species. These are more attractive food sources because pioneer plants have lower levels of secondary metabolites and higher nutrient concentrations than the shade-tolerant species that will come later.<ref name="Farji-Brener-2001">{{cite journal | last=Farji-Brener | first=Alejandro G. | title=Why are leaf-cutting ants more common in early secondary forests than in old-growth tropical forests? An evaluation of the palatable forage hypothesis | journal=Oikos | publisher=Nordic Society Oikos (Wiley) | volume=92 | issue=1 | year=2001 | issn=0030-1299 | doi=10.1034/j.1600-0706.2001.920120.x | pages=169–177 | bibcode=2001Oikos..92..169F | hdl=10088/1425}}</ref>
== Parasites ==
When the ants are out collecting leaves, they are at risk of attack by some species of phorid flies, parasitoids that lay eggs in the crevices of the worker ants' heads. Often, a minim will stand on a worker ant's leaf and ward off any attack.<ref>{{Citation |url=https://www.lpzoo.org/articles/features/Leafcutter_Ants/index.html |archive-url=https://web.archive.org/web/20080516000857/https://www.lpzoo.org/articles/features/Leafcutter_Ants/index.html |url-status=dead |archive-date=2008-05-16 |work=Lincoln Park Zoo |title=Leafcutter Ants }}</ref>
Also, the wrong type of fungus can grow during cultivation. ''Escovopsis'', a highly virulent fungus, has the potential to devastate an ant garden, as it is horizontally transmitted. ''Escovopsis'' was cultured, during colony foundation, in 6.6% of colonies.<ref>{{Citation |last1=Currie |first1=C. R. |last2=Mueller |first2=U. G. |name-list-style=amp |last3=Malloch |first3=D. |year=1999 |title=The agricultural pathology of ant fungus gardens |journal=PNAS |volume=96 |issue=14 |pages=7998–8002 |bibcode = 1999PNAS...96.7998C |doi = 10.1073/pnas.96.14.7998 |pmid=10393936 |pmc=22176 |doi-access=free }}.</ref> However, in one- to two-year-old colonies, almost 60% had ''Escovopsis'' growing in the fungal garden.<ref>{{Citation |last1=Reynolds |first1=H. T. |name-list-style=amp |last2=Currie |first2=C. R. |year=2004 |title=Pathogenicity of Escovopsis weberi: The parasite of the attine ant-microbe symbiosis directly consumes the ant-cultivated fungus |journal=Mycologia |volume=96 |issue=5 |pages=955–959 |url=http://www.mycologia.org/cgi/content/abstract/96/5/955 |doi=10.2307/3762079|jstor=3762079 |pmid=21148916 |url-access=subscription }}.</ref>
Nevertheless, leafcutter ants have many adaptive mechanisms to recognize and control infections by ''Escovopsis'' and other micro-organisms.<ref>{{Citation| last1=Goes |first1=A. C. |last2=Barcoto |first2=M. O. |last3=Kooij |first3=P. W. |last4=Bueno |first4=O. C. |last5=& Rodrigues |first5=A. |year=2020 |title= How do leaf-cutting ants recognize antagonistic microbes in their fungal crops? |journal= Frontiers in Ecology and Evolution |volume=8 |issue=95 |pages=1–12 |doi = 10.3389/fevo.2020.00095 |bibcode=2020FrEEv...8...95G |doi-access=free}}.</ref> The most common known behaviors rely on workers reducing the number of fungal spores by grooming, or removing an infected piece of the fungus garden and throwing it away at the waste dump (described as weeding).<ref>{{Citation| last1=Currie |first1=C. R. |last2=& Stuart |first2=A. E. |year=2001 |title= Weeding and grooming of pathogens in agriculture by ants |journal= Proceedings of the Royal Society of London B |volume=268 |issue=1471 |pages=1033–1039 |doi = 10.1098/rspb.2001.1605 |pmid=11375087 |pmc=1088705 }}.</ref>
== Interactions with humans ==
In some parts of their range, leafcutter ants can be a serious agricultural pest, defoliating crops and damaging roads and farmland with their nest-making activities.<ref name="Extraordinary_Animals" /> For example, some ''Atta'' species are capable of defoliating an entire citrus tree in less than 24 hours. A promising approach to deterring attacks of the leafcutter ant ''Acromyrmex lobicornis'' on crops has been demonstrated. Collecting the refuse from the nest and placing it over seedlings or around crops resulted in a deterrent effect over a period of 30 days.<ref>{{Citation |last1=Ballari |first1=S. A. |name-list-style=amp |last2=Farji-Brener |first2=A. G. |year=2006 |title=Refuse dumps of the leaf-cutting ants as a deterrent for ant herbivory: does refuse age matter? |journal=The Netherlands Entomological Society |volume=121 |issue=3 |pages=215–219 |doi=10.1111/j.1570-8703.2006.00475.x |bibcode=2006EEApp.121..215B |s2cid=85410418 }}.</ref>
== See also ==
* List of leafcutter ants * ''Atta sexdens'' * Lepiotaceae
== References ==
{{Reflist}}
== External links ==
{{commons category}} * {{cite web |url = http://www.bristolzoo.org.uk/learning/animals/invertebrates/ant |title = Leaf-cutter ant (''Atta cephalotes'')|publisher= Bristol Zoo Gardens|access-date =2006-05-12 |url-status = dead |archive-url = https://web.archive.org/web/20100327194311/http://www.bristolzoo.org.uk/learning/animals/invertebrates/ant |archive-date = 2010-03-27}} * {{cite web |url=https://www.pbs.org/wgbh/evolution/library/01/3/l_013_01.html| title = Ancient Farmers of the Amazon | publisher=PBS Evolution Library| access-date = 2009-02-22}} *[https://www.keyapa.com/leafcutters/ The Lurker's Guide to Leafcutter Ants]
{{DEFAULTSORT:Leafcutter Ant}} Category:Ants Category:Atta (ant) Category:Symbiosis Category:Folivores Category:Acromyrmex