Ant Farmers and Gardens of Fungi  Ant Farmers and Their Gardens
of Fungi  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 c