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qualities of nests and perform reconnaissance when they evaluate the possibilities. The official definition of reconnaissance, according to the Oxford English Dictionary, is "an examination of a region to ascertain strategic features through a preliminary survey," and the ants manage this by retaining information about the different potential nests and using it later to recruit for different sites. Like a person who sees an ice cream store while jogging in the morning and files away the information for dessert, the ants can remember the landmarks near a potential nest site or the odors left there, even if they are not actively house hunting at the time. If these cues are removed by an investigator, and the ants are then required to find a new home by virtue of the scientist destroying the old one, the ants can no longer distinguish among the sites.

Ants can also arrive at the best group decision almost as a by-product of individual behavior, without the need for extensive communication. Say that a tasty bit of food can be found at the other side of a deep crack in the ground from the colony. A leafy branch lies across the crevice, and the ants can either take a shorter, direct path to the food or a longer, more convoluted one, depending on which twig they use to cross. The shorter path would be more efficient, and it turns out that this is the one favored by the ants. But how did they arrive at the decision? Even for a devoted myrmecophile, it defies reason to imagine the ants testing out one path and then the other, timing both, and then sending the message to the rest of the colony that they can save their exoskeleton some wear by taking the shorter journey.

It turns out they don't have to. Franks and several other scientists determined that a much simpler process is at work. As an ant returns from a food source, she lays down an odor trail that attracts her nest mates. The more ants that have been back and forth from the colony, the stronger the attraction of a particular pathway. Thus, the shorter trip over the twig gets more use and builds up more odor, simply because it takes less time to go to and from the food, and the ants themselves reinforce the easier path as the best choice. Others follow and, voilà, the colony as a whole has made the right decision. Similar behavior allows the ants to select the easiest sites to excavate when the possible nest entrances are blocked with sand.

At least one other species of ant, the delightfully named gypsy ant, can make collective decisions about which kinds of food can be harvested singly and which require enlisting reinforcements. A group of French and Spanish researchers presented the gypsy ants with dead crickets, which could be moved by a cooperating group of ants but not by a single individual; dead shrimps, which are five hundred times heavier than a worker and must be butchered into individually transportable pieces; or sesame seeds, which as any picnicker knows can be easily borne aloft by an ant acting alone. Making off with food in a timely and efficient manner is important, because other ant species are potentially lurking nearby, ready to snatch any food left unattended. The ants were able to gauge the number of workers necessary to lift and carry the crickets depending on the size of the prey, with small crickets requiring about a dozen workers but large ones fifteen or more, and they quickly recruited an even greater number of ants to carry out the dismemberment of the shrimp before it could be detected by competitors.

Not all group decisions by insects have such a happy outcome. Although the social ants and bees get most of the attention, scientists have also examined collective behavior in forest tent caterpillars, which live in groups until they spin their cocoons and become adult moths. The caterpillars move in munching hordes through the treetops and may either linger on a particularly succulent tree or move quickly through it in search of a more nutritious set of leaves. Because of the caterpillars' discerning tastes, forests that have been attacked