Free The Meaning of Human Existence by Edward O. Wilson Page A

and ants: where we send our young men to war, ants send their old ladies. No moral lesson there, unless you are looking for a less expensive form of elder care.
    Ants that are ill move along with the aged to the nest perimeter, and even to the outside. There being no ant doctors, leaving home is not to find an ant clinic but solely to protect the rest of the colony from contagious disease. Some ants die of fungus and trematode worm infections outside the nest, allowing these organisms to disseminate their own offspring. This behavior can be easily misinterpreted. You may wonder, if you have seentoo many Hollywood films on alien invaders and zombies, as I have, whether the parasite is controlling the brain of its host. The reality is much simpler. The sick ant has a hereditary tendency to protect its nestmates by leaving the nest. The parasite, for its part, has evolved to take advantage of ants that are socially responsible.
    The most complex societies of all ant species, and arguably of all animals everywhere, are the leafcutters of the American tropics. In lowland forests and grasslands from Mexico to warm temperate South America, you find conspicuous long files of reddish, medium-sized ants. Many carry freshly cut pieces of leaves, flowers, and twigs. The ants drink sap but don’t eat solid fresh vegetation. Instead, they carry the material deep into their nests, where they convert it into numerous complex, spongelike structures. On this substrate they grow a fungus, which they do eat. The entire process, from collection of raw plant material to the final product, is conducted in an assembly line employing a sequence of specialists. The leafcutters in the field are medium in size. As they head home with their burdens, unable to defend themselves, they are harassed by parasitic phorid flies eager to deposit eggs that hatch into flesh-eating maggots. The problem is solved, mostly, by tiny sister ant workers that ride on their backs, like mahouts on elephants, and chase the flies away with flicks of their hindlegs. Inside the nest, workers somewhat smaller than the gatherers scissor the fragments into pieces about a millimeter in diameter. Still smaller ants chew the fragments into lumps and add their own fecal material as fertilizer. Even smaller workers use the gooey lumps thus created to construct the gardens. The smallest workers—the same size as the anti-fly guards—plant and tend the fungus in the gardens.
    There is one additional caste of leafcutter ants, comprising the largest workers of all. They have outsized heads swollen with adductor muscles, which close their razor-sharp mandibles with enough force to slice leather (not to mention your skin). They appear to be specialized to defend against the most dangerous predators, including especially anteaters and probably a few other sizable mammals. The soldiers stay hidden deep in the lower chambers, charging forth only when the nest is in serious trouble. During a recent field trip in Colombia, I stumbled on a way to bring these brutes to the surface with almost no effort. I knew that leafcutter nests are constructed as a giant air-conditioning system. Channels near the center accumulate exhausted, CO 2 -laden air heated by the gardens and the millions of ants living on them. As the air is warmed, it moves by convection through openings directly above. At the same time fresh air is pulled into the nest through openings to channelslocated around the periphery of the nest. I found that if I blew into the peripheral channels, allowing my mammalian breath to be carried down into the nest center, the big-headed soldiers soon came out looking for me. I admit that this observation has no practical use, unless you like the thrill of being chased by really serious ants.
    The advanced superorganisms of ants, bees, wasps, and termites have achieved something resembling civilizations almost purely on the basis of instinct. They have done so with brains one-millionth the size of