Leaf-cutting Ants

There's something endearing about the leaf-cutting ant (Atta cephalotes), a mushroom-farming insect found in lowland forests throughout Costa Rica, carrying upright in its jaws a circular green shard scissored from the leaves of a plant. At some stage in your travels you're bound to come across an endless troop of "media" workers hauling their cargo along jungle pathways as immaculately cleaned of debris as any swept doorstep.

The nests are built below ground, sometimes extending over an area of 200 square meters, with galleries to a depth of six meters. Large nests provide a home for up to five million insects. (All ant societies are composed entirely of females; males exist only to fertilize the queen and then die. And only the queen, who may boast a thousand times the body weight of a minor worker, is fertile. Hence, all other ants in the colony are her daughters.) They set off from their nests, day and night, in long columns to demolish trees, removing every shoot, leaf, and stem section by tiny section and transporting them back to their underground chambers.

They don't eat this material. Instead, they chew it up to form a compost on which they cultivate a nutritional breadlike fungus whose tiny white fruiting bodies provide them with food. The species has evolved different physical castes, each specializing in its own social tasks. Most of the workers are tiny minors ("minimas"), which tend the nest. The cutting and carrying is performed by intermediate-size workers ("medias"), guarded by ferocious-looking "majors" about three-quarters of an inch long.