A survey of the filamentous fungi other than the symbiotic one found in association with Atta sexdens rubropilosa colonies was carried out. Different fungal species (27 taxa) were isolated a few days after treating the workers with toxic baits (sulfluramid; Mirex-S), from 40 laboratory and 20 field nests. Syncephalastrum racemosum (54%) and Escovopsis weberi (21%), Trichoderma harzianum (38%) and Fusarium oxysporum (23%) were the prevalent species in laboratory and field nests, respectively. Acremonium kiliense, Acremonium strictum, E. weberi, F. oxysporum, Fusarium solani, Moniliella suaveolens and T. harzianum were found in both nests' groups. We revealed that many filamentous fungi can co-exist in a dormant state inside the nests of these insects and some of them appear to be tightly associated with this environment.