Two harvester ants (Pogonomyrmex rugosus) from adjacent nests engaging in ritual warfare, pushing in a display of force but not actually harming each other. It is thought that colonies use these mock battles to gather information about their neighbors. Knowledge about the strength of competing colonies helps ants set territorial borders without loss of life. Tucson, Arizona, USA

Solenopsis xyloni is a fire ant native to southern and western North America. Solano County, California, USA

Tetramorium hispidum, along with its sister species T. spinosum, presents an unsolved evolutionary mystery of the North American ant fauna. Tetramorium, an ubiquitous and extraordinarily diverse genus in Africa and Asia, is nearly absent in the Americas. These two species, both confined to the desert Southwest, are the only native Tetramorium in the hemisphere. When and how the ancestor of these ants arrived is not known. Tucson, Arizona, USA