Powell's Books - Review-a-Day - The Superorganism: The Beauty...

The means that ants use to find their way in the world are fascinating. It has recently been found that ant explorers count their steps to determine where they are in relation to home. This remarkable ability was discovered by researchers who lengthened the legs of ants by attaching stilts to them. The stilt-walking ants, they observed, became lost on their way home to the nest at a distance proportionate to the length of their stilts.

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From an ant's perspective, they are three-dimensional tunnels perhaps a centimeter wide that lead to food, a garbage dump, or home. If you wipe your finger across the trail of ants raiding your sugar bowl, you can demonstrate how important the pheromone trail is: as the ants reach the spot where your finger erased their trail they will become confused and turn back or wander.

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In the case of the attines, however, the varying size classes have specific jobs to do. Some cut a piece from a leaf and drop it to the ground, while others carry the leaf fragment to a depot. From there others carry it to the nest, where smaller ants cut it into fragments. Then ants that are smaller still take these pieces and crush and mold them into pellets, which even smaller ants plant out with strands of fungus. Finally, the very smallest ants, known as minims, weed and tend the growing fungus bed. These minute and dedicated gardeners do get an occasional outing, however, for they are known to walk to where the leaves are being cut and hitch a ride back to the nest on a leaf fragment. Their purpose in doing this is to protect the carrier ants from parasitic flies that would otherwise attack them. Clearly, not only did the attines beat us to agriculture, but they exemplified the concept of the division of labor long before Adam Smith stated it.

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Thus these special bacteria must be considered as comprising the third element in a triumvirate of coevolved organisms, whose fate is now so closely interwoven that they are utterly interdependent and form a single, functional whole. Humanity's dependence upon a few grains -- principally wheat and rice -- and the complete dependence on cultivated varieties of these plants by human farmers presents a similar symbiosis.

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In their native land fire ants form discrete colonies, with just one or a few queen ants at the center of each. This is how most ants live, but something very strange happened to the fire ants soon after they reached the United States. They gave up founding colonies by the traditional method of sending off flights of virgin queens, and instead began producing many small queens, which spread the colony rather in the way an amoeba spreads, by establishing extensions of the original body. Astonishingly, at the same time the ants ceased to defend colony boundaries against other fire ants. As Holldobler and Wilson put it, "With territorial boundaries erased, local populations now coalesce into a single sheet of intercompatible ants spread across the inhabited landscape." This remarkable shift was caused by a change in the frequency of a single gene.

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