The Texas horned lizard, Phrynosoma cornutum, feeds primarily on harvester ants (Pogonomyrmex) across much of its range. We quantified behavior of P. cornutum foraging on Pogonomyrmex relative to habitat and time. For the duration of their morning activity, 14 lizards were observed; we determined their use of habitat and location of ants that were captured. Lizards spent most of their time under vegetation; the type of vegetation used varied throughout the morning. Most feeding took place in the open and involved ants dispersed away from colonies. When feeding under vegetation, most feeding took place under mesquites (Prosopis), and location of mesquites under which lizards fed was nonrandom with respect to distance from entrances to colonies of ants. Feeding at entrances to colonies was restricted to a shorter period of the morning than feeding on dispersed ants. Males and females differed in use of habitat and in foraging behavior, with males more likely to feed in the open and to feed at entrances of colonies than females.