SYMBIOTIC ANTS. “Perhaps the most astounding case is that of the higher attine leaf cutting ants and their close association with Leucocoprinae fungi. Inside attine ant nests is a fungal garden, which constitutes the main source of nutrition for the workers of the colony. The two partners have been coevolving in a symbiotic relationship for an estimated 10 million years.”
http://www.pnas.org/content/112/33/10278.full