Harvester ants, the primary prey item for HLs, are not just red ants. The genus Pogonomyrmex or harvester ant, are also dark brown/black. There are several harvester ant genus that horned lizards eat. Pogonomyrmex is just one genus. There are also Messor, Myrmycocystus and numerous others. There are a minimum of 17 different genus of ants that horned lizards eat and are beneficial. You might want to try and find local supplies of ants that are available in you area and collect small supplies and test you HLs reactions to these ants. Refrigeration is an excellent way to maintain the ants and offer only a few ants at a time. In captivity, the HLs are confined and react/stress easily.

Lester G. Milroy III
Conservation Biologist