Estimates of colony densities of active colonies of ants were made at frequent intervals throughout the year in two Chihuahuan desert communities: a creosotebush bajada and mesquite-mormon tea playas fringe community. Densities of harvester ants, Pogonomyrmex, were higher on the playa site; and seed harvesters, Pheidole, were higher on the bajada. Some ant species exhibited specific habitat requirements with regard to soil type and/or plant cover: Formica perpilosa, Pogonomyrex imbericulus, Trachymyrmex smithi neomexicanus. Other species were more generally distributed. Two congeneric species pairs exhibited differences in seasonal activities suggesting competitive interactions. Peak densities of active ant colonies exceeded 4,000 colonies ha-1 on the playa and 2.000 colonies ha-1 on the bajada.