Two kinds of harvester ants are in Colorado: the Western harvester ant, Cresson (Pogonomyrmex occidentalis), and the rough harvester ant, Emery (Pogonomyrmex rugulosus). Overall, both kinds are reddish-brown and about 5 to 7mm in length. The Western harvester ant is entirely reddish-brown, while the rough harvester ant has a distinctive black head and thorax.
These grassland species of ants are typically found in open areas. It is common to find the Western harvester ant on the eastern Plains, the San Luis Valley and the grassland areas of western Colorado. The rough harvester ant lives primarily in southeastern Colorado.
The mound surrounding the nest of the harvester ant is very distinctively broad and flat. It is easily visible, 1 to 4 feet wide and 2 to 10 inches tall. The ants remove surrounding plant material, possibly to prevent shade, and replace it with small pebbles, charcoal or dead leaves, most probably for warmth. One clue to detecting the ants' presence is the large bare spots in lawns and fields created by their mounds. The ants remain in the nests during the heat of the day and hibernate in them during winter.
Harvester ants typically eat dead insects and seeds. They easily break the seeds with their strong jaws.
Harvester ants have the capability to sting. They may do so if their nests are disturbed.