Various aspects of the ecology of the Paraguayan grass-cutting ant, Acromyrmex Iandolti fracticornis (Forel), were studied in the field. Colonies were found lo linearly orient their foraging territories, partitioning the habitat in a mosaic pattern. The distance foraged by workers were found to be a function of colony size: (Log10 maximum distance foraged) = -0,5156 + 0.4121 (Log10 area of nest). Colony .pacing, however, was found to be not immediate y dependent on colony size. Colony spacing patterns are influenced by intra-specific aggression, and perhaps by the predation or execution of founding queens. Both the mound and superficial detritus heap of nests were found to favor the survivorship of forbs. Colony numbers were found to decrease significantly as grass coverage decreased and forb species became dominant.