The densities of active ant colonies were estimated in three habitats: creosotebush shrubland, grassland, and shinnery-oak mesquite dunes. Diurnal foraging patterns were studied at bait boards. Species richness of ant communities in this transitional region (8-12 species) was considerably lower than Chihuahuan Desert ant communities in an area with lower annual average rainfall. The numerically dominant species was Forelius pruinosus. Crematogaster spp. Was subdominant in all of the habitats and exhibited relatively constant activity throughout the growing season. Harvers ants, Pogonomyrmex spp. Exhibited different seasonal activity patterns in the three habitats. One species, Trachymyrmex septentrionalis, was not recorded until October, when its nests were conspicuous with discarded leaf fragments around the entrances. Several species of ants feeding at bait board extended their foraging times in comparison to colonies of the same species too distant from the bait boards for foragers to reach the baits. Only one species (Pogonomyrmex apache) exhibited a high-tolerance foraging behavior by initiating foraging at the bait boards after soil surface temperatures exceeded 40ºC and other species had ceased foraging. Foraging activity of most species continued throughout the day when cloud cover reduced soil surface temperatures to 40ºC during midday.