Leaf-cutting ants (genera Atta and Acromyrmex) have been denoted key species of American rain-forest ecosystems (Fowler et al. 1989) because of their multifarious effects on the vegetation. Being dominant herbivores, cutting up to 13% of the standing leaf crop in a colony's territory per year, they affect directly and significantly individual plants, plant communities and ecosystems (Wirth et al. 2003). The considerable ecological impact of these ants is paralleled by the well-known fact that some species strongly benefit from human-driven habitat alterations and represent prime pests throughout Latin America (Cherrett 1986). Numerous studies have documented populations of leaf-cutting ant to increase with increasing agricultural land use, deforestation and/or disturbance (Fowler et al. 1986, Jaffe & Vilela 1989, Jonkman 1979). Specifically, elevated colony densities have been recorded in (1) transformed vegetation such as pastures (Fowler 1983) and plantations (Jaffe 1986, Oliveira et al. 1998), (2) early successional forests (Vasconcelos & Cherrett 1995), and recently (3) isolated forest remnants (Terborgh et al. 2001).