Ants were among the world’s first farmers

Finding the chemical basis for the close association between the Attine ants, inhabiting an area extending from Argentina to the southern United States, and the fungus they culture is the aim of research … by Prof. Michael M. Martin of the University of Michigan. Although many animals feed on fungi, the culturing of fungus by the Attine ants is the only known example of creatures growing their own. — Science News, November 11, 1967

Update
Attine ants, a group of more than 200 species, began cultivating fungus “gardens” for food around 60 million years ago. Total codependence between the ants and fungi evolved around 30 million years ago, scientists wrote in April in Proceedings of the Royal Society B. During a global shift to a more arid climate with long seasonal dry periods, the moisture-loving fungi may have had a harder time surviving outside of ant-tended plots. Ants also became more dependent on fungi, losing, among other things, the ability to produce the amino acid arginine.