Yet the colony does just fine. Consider the way it responds quickly and effectively to changes in its environment. If patrollers this morning discover a tasty pile of seeds, additional ants will head out to look for more within minutes, and these additional ants will become foragers. Did last night’s storm damage the nest? More maintenance workers will show up to repair it, even if that requires younger nurse ants to pitch in. Depending on the challenge or the opportunity, the colony as a whole calculates quickly and precisely how many workers are needed to take care of a job, then adjusts its resources accordingly.
This flexible system, evolved during 140 million years of ant history, is one of the main reasons that the world’s fourteen thousand or so known species of ants have flourished in a bewildering variety of ecosystems, from tropical rain forests to city sidewalks. Their way of doing things may look messy, but it enables them to accomplish amazing feats, such as organize highways, build elaborate nests, and stage epic raids—all without any leadership, game plan, or the least sense of mission.
How do they do it?
Ants Aren’t Smart
Every morning in August, Deborah Gordon sets out from the Southwestern Research Station near Portal, Arizona, and drives just across the border into New Mexico to observe red harvester ants. Every afternoon, once the ants have retreated underground to escape from the blazing heat, the biologist returns to the station with a renewed sense of wonder—not that the ants are so skillful at what they do, but that they appear to be such little dummies.
“If you watch an ant try to do something, you’ll be impressed by how inept it is,” she says. “Often, it doesn’t go about things the way you think would be best, it doesn’t remember anything for very long, and it doesn’t seem to care if it succeeds.” Only one in five ants actually accomplishes what it sets out to do. “The longer you watch an ant the more you end up wanting to help it.”
Gordon doesn’t study ants as individuals, though. Her research focuses on the behavior of ant colonies. As colonies, she says, ants are capable of solving problems far beyond the abilities of individuals, such as how to find food, allocate resources, or respond to competition from neighbors.
“Ants aren’t smart,” she clarifies. “Ant colonies are.”
The central focus of Gordon’s research has been the ants’ system of task allocation, which is how a colony decides which jobs need to be done on any particular day. Given all the uncertainties that red harvesters face—from the iffy availability of food to competition from neighbors—a colony must calculate as a group how many workers to send out foraging, how many to keep on patrol, how many to hold back to tend brood, and so on.
“One of my favorite moments in the movie Antz is a scene I call the Bureau of Task Allocation,” she says of the 1998 DreamWorks animated film. “The ants are brought to some bureaucrats—they’ve got clipboards—behind a counter, and each ant is just stamped, and given its task. This, of course, is the way we organize our work, where certain individuals have the job of assigning work to other individuals. So it’s easy for us to imagine that there’s somebody in there with a clipboard, telling somebody else what to do.” But that’s not how the ants do it.
To understand the real process of task allocation, Gordon and fellow biologist Mike Greene conducted a series of experiments a few years ago with foragers. They knew that a colony, depending on circumstances, doesn’t forage every day. It might be too cold or windy to go outside, or there might be a hungry lizard waiting at the edge of the nest mound. Patrollers seem to be the key to this decision. As they return from their early-morning scouts of the neighborhood, they’re greeted near the nest entrance by a crowd of foragers. The foragers touch antennae with the patrollers, and if they bump into the right number of patrollers, the foragers are more inclined to go out. The behavior of the patrollers, in other words, informs the decisions of the foragers.
It doesn’t happen in the way you might expect, though. “The patrollers aren’t passing along anything elaborate,” Gordon says. “They’re not coming back and giving instructions to the foragers, saying go here and do this. The message is merely in the contact. And that’s what’s hardest for us to understand, because we keep falling into the temptation to think that they’re doing it the way that we would.”
To get to the bottom of this group-oriented behavior, she and Greene conducted an experiment using fake patrollers. First they captured real patrollers leaving several colonies one morning. Then, after waiting thirty minutes, they dropped tiny glass beads coated with the smell of patrollers into each nest entrance. Red harvesters, like most ants, are covered with a layer of grease that keeps them from drying out. This grease, made of hydrocarbons, carries an odor specific not only to their colony but also to their task group. “For the ants, you might say, chemicals are what vision is for us,” Greene says. When foragers inside the nest encountered the glass beads coated with patroller hydrocarbons, they took them for real patrollers.
What Gordon and Greene wanted to know was whether the rate at which foragers encountered patrollers made any difference. If it did, that might represent an important mechanism in the colony’s decision-making process. So they varied the speed at which they dropped patroller beads into each nest. In the first of four trials, they added one bead every three minutes. In the second, one bead every forty-five seconds. In the third, one bead every ten seconds. In the last, one bead every second. The results were dramatic.
In the first two trials, the relatively slow rates prompted few foragers to go out. The same was true of the fourth trial with the fastest rate. But in the third trial, when foragers encountered glass beads at just the right rate—one bead every ten seconds—they left the nest in a big rush with four times as many foragers.
“The rate needs to be about ten seconds because that must be how long an ant can remember what happened to it,” Gordon says. “If an ant has to wait forty-five seconds to meet another ant, it forgets the previous one. It’s as if the encounter never happened.” Red harvesters, it seems, have a very short attention span. If the rate is too fast, meanwhile, that may mean that something has driven foragers back to the nest, such as a predator. The rate has to be just right.
A forager’s decision, that is, doesn’t depend on it receiving instructions from a patroller or figuring out on its own what’s needed. It depends instead on the ants following a simple rule of thumb: If it meets the right number of patrollers returning at the right rate, it goes out looking for seeds. If it doesn’t, it stays put. “Nobody’s deciding whether it’s a good day or not to forage,” Gordon says. “The collective is, but no particular ant is.”
Once the first foragers leave the nest, a separate mechanism kicks in to regulate the total number of foragers that go out that day. The key encounters this time take place between foragers only. As successful foragers return to the nest with seeds, they’re met at the nest entrance by foragers waiting in reserve. This contact stimulates the inactive ants to go out. Foragers normally don’t come back until they find something. So the faster the foragers return, the faster other ants go out, enabling the colony to tune its work force to the probability of finding food.
This simple rule, applied by one forager after another in the crowded space near the entrance hole, functions like a simple calculator for the colony. The sum of all the decisions by all the ants gives the colony the answer to the question “How many foragers do we need searching for food today?”
The ants aren’t smart. The colony is.
THIS INTRIGUING BEHAVIOR, of course, isn’t unique to ants. Many groups of animals, from honeybees to herring, tackle difficult problems without direction from leaders. They do it through a phenomenon that scientists call self-organization—the first principle of a smart swarm. Although examples of self-organization appear all around us in nature, scientists