It's a humming agricultural community. Leaf-cutter ants forage for plant tissue to feed to their garden of fungus and bacteria, which then provides the ants with food. "The system is not an ant-fungus mutualism in isolation," says Cameron Currie at the University of Wisconsin, Madison. "We've been discovering other microbes within this community." There is also a parasitic fungus that attacks the garden, but bacteria growing on the ants provide antibiotics that treat the fungus — if the yeast that eats the bacteria on the ants is kept in check.