A leafcutter column carries leaf pieces to the nest, where smaller workers clean them, cut them finer, chew them into pulp and press them into a growing fungal mass. The cultivated fungus, in the genus Leucoagaricus, digests plant material the ants cannot, and produces nutrient-rich swellings called gongylidia that the ants harvest and feed to larvae.
The farm is maintained obsessively. Workers weed out spores of competing fungi, particularly the specialised parasite Escovopsis, and carry antibiotic-producing Pseudonocardia bacteria on their cuticle. Waste is moved to refuse chambers, sometimes tended by older workers who do not return to the gardens.
A mature Atta colony can hold several million workers and excavate a nest of thousands of chambers extending metres below ground. Founding queens carry a pellet of fungus from the parent nest in a mouth pocket, so the lineage of the crop can be continuous for decades. The ants are major agricultural pests in parts of the Neotropics for the same reason they are famous: they defoliate at scale, but they never digest a leaf.