Atta (ant)
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Atta is a genus of ants found in South, Central, and southern North America (including the Carribean). They belong to the subfamily Myrmicinae. Atta are commonly referred to as leafcutter ants, although that name is shared with members of the genus Acromyrmex.<ref>Template:Citation</ref>
Atta are notable for their feeding habits. Worker ants gather plant material from around their colony and carry the plant parts into the colony's underground chambers. The organic material nourishes symbiotic fungus growing inside of the colony, which the ants consume. Leafcutters don't sting, thus do not inject venom,<ref>Template:Cite journal</ref> but are known to be strong biters.
Life Cycle
As with all ants, Atta species undergo complete metamorphosis. They emerge from their eggs as a larva, which grows until it forms a pupa. Finally, the adult form emerges from the pupa.
Adult leafcutter ants are divided into different castes, which are distinct from each other in appearance and duties.
The Worker Caste
By far the greatest number of ants living in a colony belong to the worker caste. All workers are wingless females who cannot sexually reproduce. Workers gather food, excavate the nest, and care for the queen and brood. Mature colonies of Atta ants can consist of millions of workers.<ref>Template:Citation</ref>
Physically distinct forms have also been recognized within the worker and larva castes. For example, a study of Atta sexdens found that among larvae there are two distinct forms: gardeners and nurses, and within-nest generalists.<ref>Template:Cite journal</ref>
The Soldier Caste
The leafcutter soldier caste is responsible for the colony's defense. Like workers, soldiers are wingless and sexless. While some recognize soldiers as a distinct class, they are often considered a sub-caste of workers. Soldiers appear among lines of workers carrying their leaf fragments. They are recognizable by their conspicuously larger size, more formidable spines, and very large heads. These large heads house the muscles used for closing their powerful pincer-like mandibles on enemies.<ref>Template:Cite journal</ref> Soldiers should not be confused with army ants.
The Winged Male Caste
Drones are winged males which are larger than workers and soldiers. They are the only male ants who inhabit the colony, and their sole purpose is to mate with a queen during her mating or nuptial flight. Drones are fed by workers and do little or no work in the nest. Commonly among ant species, queens can live for up to 15 years and workers about 7 years, while drones survive only for 1-2 weeks. This is because once they mate with the queen, the colony no longer needs them, and they die.<ref>Template:Cite web</ref>
The Queen Caste
The queen ant plays a major role in both creating new colonies and maintaining the ant population in established ones. When a queen is ready to mate, she leaves her colony of origin and flies into the air with many drones following her. One or more may mate with her, the number depending on the species and circumstances. Once mating is accomplished, the queen finds somewhere to begin digging a nest. Inside her nest, she lays a few eggs. These will hatch into workers who will expand the nest. From there, she will continue to spawn workers and other queens. After several years, a typical queen may average laying more than 25,000 eggs per day, and over her lifetime she may produce as many as 150 million daughters.<ref name=lib>Template:Cite web</ref>
The Leafcutters' Fungus
Leafcutter workers carry fresh plant material into their subterranean nests, where a specialized species of fungus, Leucoagaricus gongylophorus grows on the plant material they bring. All the ants feed on this fungus.<ref name=lib></ref> Larvae, pupae, and adults feed on liquids produced in the fungus' bulbous tip structures, the gongylidia.
The ants are completely dependent on the fungus and provide for all of its needs. Both gain from this mutualist relationship.
Before leaving their parent colonies, Atta queens store a small amount of fungus from their home colony into their infrabuccal or fungus pockets, which is essentially a depression below the head.
This fungus stays with the queen during her nuptial flight and while mating. After she loses her wings and has dug out ground to begin her future colony, the queen uses the fungus she has brought with her and "seeds" her underground space. She doesn't eat from the fungus initially; she gives it time to grow by fertilizing it with her fecal matter. While waiting for the fungus to grow, she survives on her body fat reserves, by eating 90% of the eggs she lays, and by using nutrients made available by the degeneration of her now unneeded wing muscles.<ref name=":0">Template:Cite book</ref>
Besides their fungus, workers acquire water and nutrients from plant sap they ingest as they cut plant leaves.<ref name="Littledyke&Cherrett_1976"/>
Unique Behaviours
Often, workers are seen harvesting leaf parts well away from their nest, despite that same plant species growing closer to their nest. It's also observed that a nest's workers may harvest leaf sections from a certain species for some time, then change to another species.
Studies suggest that many factors explain these behaviours. One reason may be that the ants can't actually see where the trees are, and thus miss viable nearby food sources while scouting for food.
A unique behaviour exhibited by certain workers is that they'll climb onto cut sections of leaf and ride the leaf back to the nest as another worker carries the leaf and its passenger. Such leaf riders protect the other workers from a particular species of phorid fly that parasitises the leaf-carriers. While hitchhiking, the ants riding the leaf also work to decontaminate the leaf fragment before it arrives at the nest.<ref name="Vieira-Neto_et_al_2006" /> In fact, in any healthy ant community, there's such a complex division of labour among highly specialized forms that often the community itself is regarded as a superorganism.
Atta ants avoid plant material containing chemical compounds which are fungicidal (dangerous for the fungus), repellent, and/or toxic.<ref>Template:Citation</ref>
If Atta ants become trapped in a collapsed tunnel, they make a tapping sound, and their sisters will rescue them.<ref> Sandved and Emsley, op. cit. p. 137.</ref>
Predators
Army ants prey on leafcutter ant larvae. Birds, bats, and ground mammals feed on Atta queens searching for a nest site after mating.<ref name="lib"></ref>
Armadillos are well adapted to feed on all ant species; in Texas, Nine-banded Armadillos often feed on Texas leafcutting ants.<ref>Template:Cite web</ref>
Evolution
The leafcutter ant genera Atta and Acromyrmex split from a common ancestral species about 10 million years ago (Mya). The Trachymyrmex group and Sericomyrmex are the closest relatives to the leafcutters; they split off about 17 Mya.<ref name=":0" />
Beginning around 50 Mya, the evolutionary history of various leafcutter ant taxa has been strongly affected by ants coevolving with their fungus.<ref name="Hoyt_1996"/> During this coevolution, the fungus lost its ability to produce spores, and the ants made it their main food source. Leafcutter ants are thought to have propagated the same fungal lineage for 25 million years, during which time the ants took over the fungus's reproduction process.<ref name="Hoyt_1996"/>
Ecological effects
Atta ants are often considered ecosystem engineers, meaning that they create and modify habitats. Among their most important effects: they transfer organic matter underground, enhance soil aeration, and increase soil nutrient availability and nitrogen fixation rates.<ref name=agu>Template:Cite journal</ref>
These effects are normally regarded as beneficial to the soil. However, a study found that emissions of carbon dioxide, or CO2, over soil in which leafcutter nests were present, were 15 to 60% more than over nearby soil having no leafcutter nest below it. At the ecosystem scale, this amounted to leafcutter nests causing an increase of 0.2 to 0.7% more CO2 added to the atmosphere.<ref name=agu></ref> The emitted CO2 was produced by the large amounts of decomposing plant material stored in the leafcutters' underground nests.<ref name=agu></ref>
As human behavior and climate change increasingly fragment the tropical and subtropical parts of the Americas where leafcutters occur, leafcutter ants are becoming more abundant<ref>Template:Cite journal</ref> and their impact on soil carbon dynamics is expected to increase.
Leafcutter ants can also create gaps in forests with an otherwise closed or unbroken canopy by trimming the leaves of plants in the understory; this allows more light to hit the forest floor. They can also alter the types of trees and other plants in their area by selectively bringing seeds into the underground chambers. If the chambers aren't too deep, such seeds can send shoots upward, which reach light and grow into established plants.<ref>Template:Cite journal</ref>
Interactions With Humans
Defoliation of Desired Plants
Many people consider leafcutters to be major pests.<ref name="UrbanEntomoTAMU">Template:Cite web</ref><ref name="Lucia-et-al-2013">Template:Cite journal</ref> They can completely defoliate a wide range of ornamental, garden, and agricultural plants. Because leafcutter ants only eat the fungus they cultivate, they may not be as affected as other ants by common insecticides.<ref>Template:Cite web</ref>
As food
Atta drones are a popular ingredient in Mexican cuisine, particularly in the southern states such as Chiapas, Guerrero, Hidalgo, Puebla, Veracruz, and Oaxaca.<ref>Template:Cite web</ref> It is considered a delicacy, as well as a food of high protein content, so often it's served as a main dish, not as garnish. They may be eaten as the sole filling in tacos. A fan of chicatana dishes in Mexico describes them as "smoky and earthy, with a crunchy texture -- ahumado y terroso, con textura crujiente". <ref>Template:Cite web</ref>
In Brazil, the flying adults of leafcutter ants (locally known as tanajuras) are highly appreciated as delicacies in several regions.<ref>Template:Cite web</ref> The techniques involving their capture and cooking are considered a part of the cultural heritage of people of the Tianguá municipality, in Ceará.
The native Guanes people of central Colombia first began cultivating and cooking the insects in the 7th century. They also used the ants' sharp pincers as stitches to heal wounds. Later the marauding Spanish conquistadors adopted the habit.Template:Citation needed
Leafcutter Ants in Popular Culture
Princess Atta from A Bug's Life was named after the leafcutter genus Atta.<ref name="Shaffer2017">Template:Cite book</ref>
In Atta (novel), a man is shrunk by a bolt of lightning and befriends an ant named Atta.<ref name="Atta_book">Template:Cite book</ref>
Species
- Atta bisphaerica Forel, 1908
- Atta capiguara Gonçalves, 1944
- Atta cephalotes (Linnaeus, 1758) -- central Mexico south throughout most of northern South America
- Atta colombica Guérin-Méneville, 1844
- Atta cubana Fontenla Rizo, 1995 -- Cuba
- Atta goiana Gonçalves, 1942
- Atta insularis Guérin-Méneville, 1844
- Atta laevigata (F. Smith, 1858) (Colombia south to Paraguay)
- Atta mexicana (Smith, 1858) -- Arizona and Texas in the US south into Nicaragua
- Atta opaciceps Borgmeier, 1939
- Atta pilosa (Buckley, 1866) -- AntWiki considers this taxon to be unidentifiable and its identity uncertain
- Atta robusta Borgmeier, 1939
- Atta saltensis Forel, 1913
- Atta sexdens (Linnaeus, 1758)
- Atta tardigrada (Buckley, 1866)
- Atta texana (Buckley, 1860) - Texas leafcutter ant (East Texas and western Louisiana in the United States, northeastern Mexico)
- Atta vollenweideri Forel, 1893