Red harvester ants of the genus Pogonomyrmex played a central role as vision-inducing agents in the religious and medical systems of many indigenous groups in southern and south-central California. The ants were ingested alive in massive quantities in order to induce prolonged catatonic states, during which hallucinogenic visions were reported to manifest. They also played an important role in both curative and preventative medicine, treating a diverse body of natural and supernatural ailments. In this article I present an ethnographic and toxicological overview of the ritual and therapeutic use of red ants, bringing together both published and unpublished accounts in an attempt to reconstruct this poorly-known facet of indigenous California culture. The data presented in this paper strongly suggest that, through either direct or indirect action on the central nervous system, massive quantities of Pogonomyrmex venom are capable of producing highly altered metabolic states during which hallucinatory visions are apt to manifest. This topic is of considerable interest, as it is the first well-documented ethnographic example of an hallucinogenic agent of insect origin.