Leafcutter Ant | Insect Tribe - Britannica

Ecological importance

Leafcutters are the dominant herbivores of the New World tropics. The amount of vegetation cut from tropical forests by the Atta ants alone has been estimated at 12–17 percent of all leaf production. Grass-cutting species accomplish similar feats: one species, A. capiguara, reduces the commercial value of pasture land in Brazil and Paraguay by as much as 10 percent.

Leafcutter ants profoundly affect their surroundings. By pruning vegetation, they stimulate new plant growth, and, by gardening their fungal food, they enrich the soil. Excavating nests that may occupy 23 cubic meters (800 cubic feet), a colony of A. sexdens leafcutters may turn over 40,000 kg (88,000 pounds) of soil in tropical moist forests, stimulating root growth of many plant species. In New World tropical rainforests, the large nests of these ants are often found among large trees that are spaced far apart with little undergrowth—a parklike setting created by the ants themselves. Many Atta species clear ant “highways” radiating out from the nest, along which wide columns of their kind can march unhindered.

Related Topics: harvester ant Atta Atta sexdens Atta cephalotes Atta capiguara (Show more) See all related content Explore Britannica Premium!

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Though voracious, leafcutter ants are not indiscriminate in their harvests. At a study site in Costa Rica, A. cephalotes attacked only 17 of 332 available plant species, selecting woody species over herbaceous ones and introduced species over natives. Members of the plant families Asteraceae, Solanaceae, and Euphorbiaceae are frequently attacked. Within the favored species, the ants prefer freshly sprouted leaves, flowers, and shoots. Some ant lineages specialize on certain types of plants, and some plants are preferred on a seasonal basis; some plants are avoided altogether. In the case of the Hymenea tree genus, this observation led to the discovery of antifungal chemicals. Species that are avoided tend to possess compounds called terpenoids, which may be toxic to the ants’ fungi. These include many trees used by indigenous tribes for medicinal purposes or fungicides.