Fungus-growing ants

Early ancestors of attine ants were probably insect predators. They likely began foraging for leaf sections, but then converted their primary food source to the fungus these leaf cuts grew. Higher attines, such as Acromyrmex and Atta, are believed to have evolved in Central and North America about 20 million years ago (Mya), starting with Trachymyrmex cornetzi. While the fungal cultivars of the 'lower' attine ants can survive outside an ant colony, those of 'higher' attine ants are obligate mutualists. The fungus the ants grew eventually became reproductively isolated and co-evolved with the ants. These fungi gradually began decomposing more nutritious material like fresh plant-material. Shortly after attine ants began keeping their fungus gardens in dense aggregations, their farms likely began suffering from a specialized genus of Escovopsis, which are mycopathogens. The ants evolved cuticular cultures of Actinomycetota that suppress Escovopsis and possibly other bacteria. These cuticular cultures are both antibiotics and antifungals. The mature worker ants wear these cultures on their chest plates and sometimes on their surrounding thoraces and legs as a biofilm. == Behavior ==

Mating Typically, one queen ant lives per colony. Every year after the colony is about three years old, the queen lays eggs of female and male alates, the reproductive ants that will pass on the genes of the queens. Before leaving the nest, queens stuff some of the fungus' mycelia in her cibarium. These winged males and queens then take their nuptial flights to mate high in the air. In some areas, species flights are synchronized with all local colonies' virgin royalty flying at the same time on the same day, such as Atta sexdens and Atta texana. Until the first workers have matured, the ant queen is the sole worker. She grows the garden, fertilizing it with her fecal liquid, but does not eat from it. Instead, she gains energy from eating 90% of the eggs she lays, in addition to catabolizing her wing muscles and fat reserves. == Caste system ==

Attines have seven castes performing roughly 20–30 tasks, meaning the potential exists for development of more specialized castes performing individual tasks for Atta's future.'' workers demonstrating the common polymorphism of higher attines Behavior Though all castes defend their nests in the event of invasion, a true soldier caste, with individuals called majors, exists. They are larger than other workers, and use their large, sharp mandibles, powered by huge adductor muscles, to defend their colonies from large enemies, such as vertebrates. When a foraging area is threatened by conspecific or interspecific ant competitor, the majority of respondents are smaller workers from other castes, since they are more numerous, and therefore better suited for territorial combat. All size groups defend their colonies from invaders, but older workers have been found to attack and defend territories most often. At least three of four physical castes of A. sexdens change their behavior based on their age. == Habitat ==

Lower attines mostly live in inconspicuous nests with 100–1000 individuals and relatively small fungus gardens in them. Higher attines, in contrast, live in colonies made of 5–10 million ants that live and work within hundreds of interconnected fungus-bearing chambers in huge subterranean nests. Some colonies are so large, they can be seen from satellite photos, measuring up to . == Farming ==

The majority of fungi that are farmed by attine ants come from the family Agaricaceae, mostly from the genera Leucoagaricus and Leucocoprinus, though variance occurs within the tribe. Some species in the genus Apterostigma have changed their food source to fungi in the family Tricholomataceae. Some species cultivate yeast, such as Cyphomyrmex rimosus. It was previously assumed that the cultures are always transmitted vertically from colony to young queen, but some lower attines have been found to be growing recently domesticated Lepiotaceae. Some species transfer cultures laterally, such as Cyphomyrmex and occasionally some species of Acromyrmex, whether by joining a neighboring tribe, stealing, or invading another colony's garden. worker taking a leaf to its colony Lower attines do not use leaves for the majority of the substrate for their gardens, and instead prefer dead vegetation, seeds, fruits, insect feces, and corpses. The lower attine ant species Mycocepurus goeldii has been found to farm Leucocoprinus attinorum whilst the sand dwelling Mycetophylax morschi farms the closely related species Leucocoprinus dunensis. Apterostigma dentigerum cultivates Myrmecopterula velohortorum in veiled hanging gardens whereas Apterostigma manni cultivates Myrmecopterula nudihortorum in spongelike masses in cavities in the ground or under logs. Worker recruitment The number of ants that are recruited to cut varies greatly based on the leaf quality available in addition to the species and location of the colony. Leaf quality is complex to measure because many variables exist, including "leaf tenderness, nutrient composition, and the presence and quantity of secondary plant chemicals" such as sugar. Studies suggest there are two purposes for marking the trails this way: worker recruitment and orientation cues. The trail recruitment pheromone methyl-4-methylpyrrole-2-carboxylate (MMPC), was the first whose chemical structure was identified. It is also the main trail recruitment pheromone in all Atta species except Atta sexdens, which uses 3-ethyl-2,5-dimethylpyrazine. MMPC is incredibly potent and effective at attracting ants. One milligram is theoretically powerful enough to create a path that A. texana and A. cephalotes would follow three times the Earth's circumference [] and that 50% of A. vollenweideri foragers would follow 60 times around the Earth []. Harvesting vegetation Most harvesting sites are in tree canopies or patches of savanna grasses. The sizes of leaf fragments have been found in some studies to vary based on the size of ants due to the ants' anchoring of their hind legs while cutting, though other studies have not found correlations. This is likely because many factors affect how ants cut leaves, including neck flexibility, body axis location, and leg length. Often, ants stridulate while cutting vegetation by raising and lowering their gasters in a way that makes a cuticular file on the first gastric tergite and a scraper on the postpetiole rub together. This makes a noise, audible by people with great hearing sitting very close to them and visible using laser-Doppler vibrometry. The metabolic rate of the ants while and after cutting vegetation is above standard. Their aerobic scope is in the range of flying insects, which are among the most metabolically active animals. Data does not show that this behavior maximizes load transportation, so scientists have explained this behavior in other ways, though the data are still inconclusive. One theory is that this type of task partitioning increases the efficiency of individual workers as they become specialists. Another is that the chains accelerate communication between ants about the quality and species of the plants being cut, recruits more workers, and reinforces territorial claims by reinforcing the scent markings. Gardening process First, foragers bring in to and drop leaf fragments on the nest's chamber floor. Workers that are usually slightly smaller clip these pieces into segments that are about across. Smaller ants then crush these fragments and mold them into damp pellets by adding fecal droplets and kneading them. They add the pellets into a larger pile of other prill. Cellulose has been found to be poorly degraded and assimilated by fungus, if at all, meaning that the ants that eat the fungus do not get much energy from the cellulose in plants. Xylan, starch, maltose, sucrose, laminarin, and glycoside apparently play the important roles in ant nutrition. It is not known yet how ants can digest laminarin, but myrmecologists E.O. Wilson and Bert Hölldobler hypothesize that fungal enzymes may occur in the ants' guts, as evidenced by the enzymes found in larval extract. Larvae seem to grow on all or nearly all fungi, whereas queens obtain their energy from the eggs nonqueen females lay and workers feed to them. Pseudonocardia has been identified as a defensive symbiont for the Attinae ants. It is a filamentous and sporulating bacteria that grows slowly in aerobic conditions. Like the fungus, virgin queens take a culture of the bacterial symbiont that they then pass to their new workers when establishing a colony. However, this relationship has not always existed and can be gained or lost in the attine phylogeny. In addition to the anti-fungal compounds, there is some evidence that the Pseudonocardia also produces anti-bacterial compounds. A colony can "[defoliate] a mature eucalyptus tree overnight". The cutting of leaves to grow fungus to feed millions of ants per colony has a large ecological impact in the subtropical areas in which they reside. ==Genera==

Extant • Acanthognathus • Acromyrmex • Allomerus • Amoimyrmex • Apterostigma • Atta • Basiceros • Blepharidatta • Cephalotes • Chimaeridris • Colobostruma • Cyatta • Cyphomyrmex • Daceton • Diaphoromyrma • Epopostruma • Eurhopalothrix • Ishakidris • Kalathomyrmex • Lachnomyrmex • Lenomyrmex • Mesostruma • Microdaceton • Mycetagroicus • Mycetarotes • Mycetomoellerius • Mycetophylax • Mycetosoritis • Mycocepurus • Myrmicocrypta • Ochetomyrmex • Octostruma • Orectognathus • Paramycetophylax • Phalacromyrmex • Pheidole • Pilotrochus • Procryptocerus • Protalaridris • Pseudoatta • Rhopalothrix • Sericomyrmex • Strumigenys • Talaridris • Trachymyrmex • Tranopelta • Wasmannia • Xerolitor Extinct • †Attaichnus (trace fossil) ==See also==