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| Atta | |
|---|---|
 | |
| Queen ofAtta colombica tending her fungus | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Family: | Formicidae |
| Subfamily: | Myrmicinae |
| Tribe: | Attini |
| Genus: | Atta Fabricius, 1805 |
| Type species | |
| Atta cephalotes | |
| Diversity[1] | |
| 17 species | |
| Synonyms | |
| |
Atta is agenus ofants found in South, Central, and southern North America (including the Caribbean). They belong to thesubfamilyMyrmicinae.Atta are commonly referred to asleafcutter ants, although that name is shared with members of the genusAcromyrmex.[2]
Atta are notable for their feeding habits. Worker ants gather plant material from around theircolony and carry the plant parts into the colony's underground chambers. The organic material nourishes symbioticfungus growing inside of the colony, which the ants consume. Leafcutters don't sting, thus do not inject venom,[3] but are known to be strong biters.
As with all ants,Atta species undergocomplete metamorphosis. They emerge from their eggs as alarva, which grows until it forms apupa. Finally, the adult form emerges from the pupa.
AdultAtta ants are divided into differentcastes, which are distinct from each other in appearance and duties.
The greatest number of ants living in anAtta colony belong to theworker caste. All workers are wingless females who cannotsexually reproduce. Workers gather food, excavate the nest, and care for the queen and brood. Mature colonies ofAtta ants can consist of millions of workers.[4]
Physically distinct forms have also been recognized within the worker and larva castes. For example, a study ofAtta sexdens found that among larvae there are two distinct forms: gardeners and nurses, and within-nest generalists.[5]
TheAttasoldier 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-likemandibles on enemies.[6] Soldiers should not be confused witharmy ants.
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 ornuptial 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 seven 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.[7]
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. A typical queen lays more than 25,000 eggs per day and 150 million eggs over her lifetime.[8]
Atta 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.[8] Larvae, pupae, and adults feed on liquids produced in the fungus' bulbous tip structures, thegongylidia. The ants are completely dependent on the fungus and provide for all of its needs. Both gain from thismutualist relationship.
Before leaving their parent colonies,Atta queens store a small amount of fungus from their home colony into their infrabuccal orfungus pockets, which is a depression below the head. This fungus stays with the queen during her nuptial flight and while mating. After she loses her wings and digs out ground to begin her future colony, the queen uses the fungus she has brought with her to "seed" her underground space, fertilizing the fungus with herfecal 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.[9]
Besides their fungus, workers acquire water and nutrients from plant sap they ingest as they cut plant leaves.[10]
Workers ants often harvest 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 switch to another species. Studies suggest that many factors explain these behaviours, such as the ant's potential inability to see where the plants are.
Certain workers climb onto cut sections ofleaf 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 ofphorid fly thatparasitises the leaf-carriers. While hitchhiking, the ants riding the leaf also work to decontaminate the leaf fragment before it arrives at the nest.[11] Ant communities that exhibit this complexdivision of labour among highly specialized forms are often regarded assuperorganisms.
Atta ants avoid plant material containingchemical compounds which arefungicidal (dangerous for the fungus), repellent, and/ortoxic.[12]
IfAtta ants become trapped in a collapsed tunnel, they make a tapping sound, and their sisters will rescue them.[13]
Army ants prey onAtta ant larvae. Birds, bats, and ground mammals feed onAtta queens searching for a nest site after mating.[8]
Armadillos are well adapted to feed on all ant species; in Texas, Nine-banded Armadillos often feed onTexas leafcutting ants.[14]
The leafcutter ant generaAtta andAcromyrmex split from a common ancestral species about 10 million years ago (Mya). TheTrachymyrmex group andSericomyrmex are the closest relatives to the leafcutters; they split off about 17 Mya.[9]
Beginning around 50 Mya, the evolutionary history of various leafcutter anttaxa has been strongly affected by antscoevolving with their fungus.[15] 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.[15]
Atta ants are often consideredecosystem engineers, meaning that they create and modifyhabitats. They transferorganic matter underground, enhancesoil aeration, and increasesoil nutrient availability andnitrogen fixation rates.[16]
A study found that emissions ofcarbon dioxide, or CO2, over soil in whichAtta nests were present were 15–60% more than over nearby soil with noAtta nests. At the ecosystem scale, this amounted toAtta nests causing an increase of 0.2 to 0.7% more CO2 added to the atmosphere.[16] The emitted CO2 was produced by the large amounts of decomposing plant material stored in theAtta's underground nests.[16]
As human behavior and climate change increasingly fragment the tropical and subtropical parts of theAmericas,Atta ants are becoming more abundant[17] and their impact onsoil carbon dynamics is expected to increase.
Atta ants can also creategaps in forests with an otherwise closed or unbrokencanopy by trimming the leaves of plants in theunderstory; this allows more light to hit theforest 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.[18]
Many people considerAtta ants to be majorpests.[19][20] They can completely defoliate a wide range of ornamental, garden, and agricultural plants. BecauseAtta ants only eat the fungus they cultivate, they may not be as affected as other ants by commoninsecticides.[21]
Atta drones are a popular ingredient inMexican cuisine, particularly in the southern states such asChiapas,Guerrero,Hidalgo,Puebla,Veracruz, andOaxaca.[22] It is considered a delicacy, as well as a food of high protein content, so often it's served as a main dish. They may be eaten as the sole filling intacos. A fan ofchicatana dishes in Mexico describes them as "smoky and earthy, with a crunchy texture --ahumado y terroso, con textura crujiente".[23]
InBrazil, the flying adults ofAtta ants (locally known astanajuras) are highly appreciated as delicacies in several regions.[24] The techniques involving their capture and cooking are considered a part of thecultural heritage of people of theTianguá municipality, inCeará.
The nativeGuanes people of centralColombia first began cultivating and cooking the insects in the 7th century. They also used the ants' sharp pincers as stitches to heal wounds. The marauding Spanishconquistadors later adopted the habit.[citation needed]
Princess Atta fromA Bug's Life was named after the leafcutter genusAtta.[25]
InAtta (novel), a man is shrunk by a bolt of lightning and befriends an ant named Atta.[26]
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