Because they have such a propensity to cut and gather leaves, it was long believed that these ants from Central and South America also ate the leaves they collected.
That all changed in 1874, when a mining engineer by the name of Thomas Belt (whose hobby was natural history) published "A Naturalist in Nicaragua." In the book, he wrote: "I believe the real use they make of them is as a manure, on which grows a minute species of fungus, on which they feed — that they are, in reality, mushroom growers and eaters."
Belt was correct. Leaf-cutter ants don't actually eat leaves. Instead, they gather leaves to cultivate a fungus that grows on them, and then they eat the fungus.