Inside Animal Minds: The New Science of Animal Intelligence by and Peter Miller Mary Roach Virgina Morell Read Free Book Online

return. As patrollers enter the nest, they touch antennae briefly with foragers.
    “When a forager has contact with a patroller, it’s a stimulus for the forager to go out,” Gordon says. “But the forager needs several contacts no more than ten seconds apart before it will go out.”
    To see how this works, Gordon and her collaborator Michael Greene of the University of Colorado at Denver captured patroller ants as they left a nest one morning. After waiting a half hour, they simulated the ants’ return by dropping glass beads into the nest entrance at regular intervals—some coated with patroller scent, some with maintenance worker scent, some with no scent. Only the beads coated with patroller scent stimulated foragers to leave the nest. Their conclusion: Foragers use the rate of their encounters with patrollers to tell if it’s safe to go out. (If you bump into patrollers at the right rate, it’s time to go foraging. If not, better wait. It might be too windy, or there might be a hungry lizard waiting out there.) Once the ants start foraging and bringing back food, other ants join the effort, depending on the rate at which they encounter returning foragers.
    “A forager won’t come back until it finds something,” Gordon says. “The less food there is, the longer it takes the forager to find it and get back. The more food there is, the faster it comes back. So nobody’s deciding whether it’s a good day to forage. The collective is, but no particular ant is.”
    That’s how swarm intelligence works: Simple creatures are following simple rules, each one acting on local information. No ant sees the big picture. No ant tells any other ant what to do. Some ant species may go about this with more sophistication than others. (
Temnothorax albipennis
, for example, can rate the quality of a potential nest site using multiple criteria.) But the bottom line, says Iain Couzin, a biologist at Oxford and Princeton Universities, is that no leadership is required. “Even complex behavior may becoordinated by relatively simple interactions,” he says.
    Inspired by the elegance of this idea, Marco Dorigo, a computer scientist at the Université Libre in Brussels, used his knowledge of ant behavior in 1991 to create mathematical procedures for solving particularly complex human problems, such as routing trucks, scheduling airlines, or guiding military robots.
    In Houston, for example, a company named American Air Liquide has been using an ant-based strategy to manage a complex business problem. The company produces industrial and medical gases, mostly nitrogen, oxygen, and hydrogen, at about a hundred locations in the United States and delivers them to 6,000 sites, using pipelines, railcars, and 400 trucks. Deregulated power markets in some regions (the price of electricity changes every 15 minutes in parts of Texas) add yet another layer of complexity.
    “Right now in Houston, the price is $44 a megawatt for an industrial customer,” says Charles N. Harper, who oversees the supply system at Air Liquide. “Last night the price went up to $64, and Monday when the cold front came through, it went up to $210.” The company needed a way to pull it all together.
    Working with the BiosGroup (now NuTech Solutions), a firm that specialized in artificial intelligence, Air Liquide developed a computer model based on algorithms inspired by the foraging behavior of Argentine ants
(Linepithema humile)
, a species that deposits chemical substances called pheromones.
    “When these ants bring food back to the nest, they lay a pheromone trail that tells other ants to go get more food,” Harper explains. “The pheromone trail gets reinforced every time an ant goes out and comes back, kind of like when you wear a trail in the forest to collect wood. So we developed a program that sends out billions of software ants to find out where the pheromone trails are strongest for our truck routes.”
    Ants had evolved an efficient method to