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Published on Feb 6, 2018
Leaf-cutter ants | Atta (genus) Leaf-cutter ants | Atta (genus) Leaf-cutter ants | Atta (genus)
Atta is a genus of New World ants of the subfamily Myrmicinae. It contains at least 17 known species.
Leaf-cutter ants are relatively large, rusty red or brown in colour, and have a spiny body and long legs. The three main castes within a nest are the queen, worker and soldier. Only the queens and males have wings, and these ants are also known as 'reproductives' or 'swarmers'. Although most of the ants in the nest are female, only the queens produce eggs. Queens are usually over 20 mm long.
Evolution Leaf cutter ants are very specialized organisms in that they coevolved with another organism through symbiosis. This process took millions of years to occur, about 50 million years ago, which is when these ants began their relationship with plants. The fungus eventually lost the ability to produce spores and the ants capitalized on that by making the fungus its main food source. About 66 million years ago, South America was isolated from other land masses, and this is when gardening ants started their relationship with a fungus. It has been hypothesized that leafcutter ants propagated the same fungal lineage for 25 million years, which means they caused the fungus to reproduce itself. The leafcutter ants are different from other ants by their underground fungi cultivation; they have not been thought to be derived from another ant, but they bear a resemblance to the harvester ant, Pogonomyrmex. Ecological effects Leafcutter ants can create bottom-up gaps by forming their large nests. The ants excavate soil rich in organic matter, and store additional organic matter in their underground chambers. This creates rich soils that promote plant growth. The ants can also trim the leaves of plants in the understory, allowing for more light to hit the forest floor. They can also control the types of trees and other plants by selectively bringing seeds into the underground chambers. Depending on the location of the chamber, a seed can grow by reaching light.