Horned lizards, Phrynosoma cornutum, were observed between sunrise and sunset in order to record the time spent at different behaviors and the prey taken. Two ant species, Pogonomyrmex desertorum and Pogonomyrmex rugosus, were the most important prey. The behavioral responses of these prey species were studied by subjecting them to varying levels of simulated predation.... The horned lizards have evolved a foraging strategy that allows maximization of prey availability over weeks or a month rather than per hour or day. Estimates of horned lizard densities, ingestion rates, and numbers of potential prey suggest that horned lizard numbers are regulated by the availability and productivity of Pogonomyrmex spp. These estimates also suggest Pogonomyrmex spp. colonies are extremely productive, essentially replacing the entire worker population each year.