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It’s not clear precisely how and why some ancestral species of ant first took up fungus farming, but scientists have determined by genetic testing that it happened about 50 million years ago.
Today, several species of ant (including the famed leaf-cutters of Central and South America) carefully tend and nurture gardens of fungi in vast underground nests.
Ants lack the necessary enzymes to digest leaves and stems themselves, so they cut them up and feed them to the fungi, which break down cellulose (the tough fibrous material in plant tissues), making nutrients available to the ants.
The ants excavate nests and build nice, cozy, safe chambers for their fungal gardens; they clean off debris and parasites from the fungi; and even produce special antibiotics in their bodies to ward off or kill infectious organisms that might attack their crops.
In return, the fungi produce swellings at the tips of their hyphae (long strings of fungal cells) that are rich in proteins, sugars and other nutrients. The ants dine on these nutritious swellings, called gongylidia.
The fungi are ensured a copious food supply and a stable, nurturing environment in which to live.
The fungi rely upon the ants for reproduction. Before new queen ants fly off to mate and found their own colonies, they tuck a bit of fungus in their mandibles to start their new gardens. The fungi growing in virtually every leaf-cutter garden are actually clones of the same fungus farmed by ants 25 million years ago.