Of Ants and Men
By Tim Flannery
Parallels between the ants and ourselves are striking for the light they shed on the nature of everyday human experiences. Some ants get forced into low-status jobs and are prevented from becoming upwardly mobile by other members of the colony. Garbage dump workers, for example, are confined to their humble and dangerous task of removing rubbish from the nest by other ants who respond aggressively to the odors that linger on the garbage workers’ bodies.
Some of the most fascinating insights into ants have come from researchers who measure the amount of carbon dioxide given off by colonies. This is rather like measuring the respiration rate in humans in that it gives an indication of the amount of work the superorganism is doing. The researchers discovered (perhaps unsurprisingly) that colonies experiencing internal conflict between individuals seeking to become reproductively dominant produce more CO2 than do tranquil colonies where the social order is long established. But extraordinarily, they also discovered that about three hours after removing a queen ant, the CO2 emissions from a colony drop. “Removing the queen thus has a clear effect on worker behavior, apparently reducing their inclination to work for the colony,” the researchers concluded. While it is dangerous to anthropomorphize, it seems that ants may have their periods of mourning just as we humans do when a great leader passes from us.
However, ants clearly are fundamentally different from us. A whimsical example concerns the work of ant morticians, which recognize ant corpses purely on the basis of the presence of a product of decomposition called oleic acid. When researchers daub live ants with the acid, the undertakers promptly carry off the acid-daubed ants to the ant cemetery, despite the fact that they are alive and kicking. Indeed, unless they clean themselves very thoroughly they are repeatedly dragged to the mortuary, despite showing every other sign of life.
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.
The principal tools ants use, however, in guiding their movements and actions are potent chemical signals known as pheromones. So pervasive and sophisticated are pheromones in coordinating actions among ants that it’s appropriate to think of ants as “speaking” to each other through pheromones. Around forty different pheromone-producing glands have been discovered in ants, and, although no single species has all forty glands, enough diversity of signaling is present to allow for the most sophisticated interactions. The fire ant, for example, uses just a few glands to produce its eighteen pheromone signals, yet this number, along with two visual signals, is sufficient to allow its large and sophisticated colonies to function.
Pheromone trails are laid by ants as they travel, and along well-used routes these trails take on the characteristics of a superhighway. From the 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. The chemicals used to mark such trails are extraordinarily potent. Just one milligram of the trail pheromone used by some species of attine ants to guide workers to leaf-cutting sites is enough to lay an ant superhighway sixty times around the earth.
Ant sex seems utterly alien. Except for short periods just before the mating season, when an ant colony is reproducing, it is composed entirely of females, and among some primitive species virgin births are common. All the offspring of such virgin mothers, however, are winged males that almost invariably leave the nest. If a female ant mates, however, all of her fertilized eggs become females. In many ant societies, reproduction is the prerogative of a single individual—the queen. She mates soon after leaving her natal colony and stores the sperm from that mating (or from multiple matings) all of her life, using it to fertilize (in some cases) millions of eggs over ten or more years.
The progress of ants from this relatively primitive state to the complexity of the most finely tuned superorganisms leaves no doubt that the progress of human evolution has largely followed a path taken by the ants millions of years earlier. Beginning as simple hunter-gatherers, some ants have learned to herd and milk bugs, just as we milk cattle and sheep. There are ants that take slaves, ants that lay their eggs in the nests of foreign ants (much as cuckoos do among birds), leaving the upbringing of their young to others, and there are even ants that have discovered agriculture. These agricultural ants represent the highest level of ant civilization, yet it is not plants that they cultivate but mushrooms. These mushroom farmers are known as attines, and they are found only in the New World. Widely known as leafcutter ants, they are doubtless familiar from wildlife documentaries.
The attines, say Hölldobler and Wilson, are “Earth’s ultimate superorganisms,” and there is no doubt that their status is due to their agricultural economy, which they developed 50 to 60 million years before humans sowed the first seed. Indeed, it is in the changes wrought in attine societies by agriculture that the principal interest for the student of human societies lies. The most sophisticated of attine ant species has a single queen in a colony of millions of sterile workers that vary greatly in size and shape, the largest being two-hundred times heavier than the smallest. Their system of worker specialization is so intricate that it recalls Swift’s ditty on fleas:
So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite ‘em;
And so proceed ad infinitum.
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.
You may not believe it, but, like the sailors of old, the leafcutter ants “sing” as they work. Leaf-cutting is every bit as strenuous for the ants as hauling an anchor is for human beings, and their singing, which takes the form of stridulation (a sound created by the rubbing together of body parts), assists the ants in their work by imparting vibrations to the mandible that is cutting the leaf, enhancing its action in a manner akin to the way an electric knife helps us cut roasts. The leafcutters also use stridulation to cry for help, for example when workers are trapped in an underground cave-in. These cries for help soon prompt other ants to rush in and begin digging until they’ve reached their trapped sisters.
One can hardly help but admire the intelligence of the ant colony, yet theirs is an intelligence of a very particular kind. “Nothing in the brain of a worker ant represents a blueprint of the social order,” Hölldobler and Wilson tell us, and there is no overseer or “brain caste” that carries such a master plan in its head. Instead, the ants have discovered how to create strength from weakness by pooling their individually limited capacities into a collective decision-making system that bears an uncanny resemblance to our own democratic processes.
©Tim Flannery, The New York Review of Books 2009
Photo ©Anne Clark/Getty Images