Seasonal activity, factors affecting foraging activity and forage selection were studied in three species of Pheidole (Hyminoptera: Formicidae) on a watershed in the southern New Mexico Chihuahuan Desert. Pheidole spp. exhibited a seasonal pattern in numbers of active colonies with most colonies active in July coincident with onset of summer rains and seed drop by annual plants. Pheidole militicida occurred only on the deeper soils of the lower watershed while Ph. rugulosa and Ph. xerophila occurred on the entire watershed. The three Pheidole spp. were active only at soil temperatures between 15-35C and were most active at sunrise. Analysis of factors affecting foraging intensity using a stepwise discriminant function and regression showed evaporation and soil surface temperature to be the strongest influences and seed availability to rank second. However, the factors included in the analysis accounted for less than 50% of the variance in all three species. Pheidole militicida collected mostly forb seeds while Ph. xerophila utilized primarily grass seeds, especially the seeds of fluff grass Erioneuron pulchellum.