The nest architecture of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae).

Nests of species of the genus Atta are, structurally, the most complex among those of the Attini tribe. The objective of this research was to describe external and internal characteristics of nests of the leaf-cutting ant Atta sexdens (L. 1758) (Hymenoptera: Formicidae) in Vitória da Conquista, Bahia state, Brazil. Ten nests (N1 to N10) of this ant were selected and their external architecture described according to the loose soil removed from excavations by ant forage workers. The length and width of foraging trails and the distance of their entrance holes to the mound of loose soil in nests of this ant were measured. The internal architecture and the number, shape, dimensions and depth of the internal chambers and tunnels of the N1, N2 and N3 nests, with loose soil areas of 78.02, 8.06 and 4.78 m2, respectively, were described and measured. The nest N1 was excavated without moulding and the N2 and N3 moulded with 5 kg of cement in 10 L of water and subsequently excavated. Trenches, one meter deep, were made before excavation began and widened and deepened until exposing the chambers and tunnels of these nests. The ants deposited loose soil irregularly, forming small mounds around the entrance holes of their nests. Fungus and empty chambers are spherical with twig-like branches. The inner sections of the tunnels are elliptical or circular with different dimensions.