The purpose of this study was to determine if black-tailed prairie dogs (Cynomys ludovicianus Ord) influence harvester ant nest density and species composition within the shortgrass prairie biome of southwestern Kansas. Two treatments were established: areas colonized by prairie dogs and areas not colonized by prairie dogs. We recorded 183 harvester ant nests of 3 species. Harvester ant nest density did not differ significantly between prairie dog colonies (3.08 nests ha -1 ) and non-colonized shortgrass prairie sites (4.54 nests ha -1 ), but species composition did. Pogonomyrmex rugosus Emery was the most frequent species on prairie dog colonies where it accounted for 87% of ant nests present, as opposed to 33% on sites where prairie dogs were absent. Pogonomyrmex barbatus Smith was the most abundant species on non-colonized areas, making up 49% of the ant nests sampled. Pogonomyrmex occidentalis Cresson comprised 11% of ant nests sampled, and was nearly absent from prairie dog colonies (20 nests on non-colonized sites vs. 1 nest on prairie dog colonies). The average number of harvester ant species found per site was consistently greater on sites where prairie dogs were absent.