Ants are so much a part of our everyday lives that unless we discover them in our sugar bowl we rarely give them a second thought. Yet those minuscule bodies voyaging across the kitchen counter merit a closer look, for as entomologists Bert Hölldobler and Edward O. Wilson tell us in their latest book, they are part of a superorganism. Superorganisms such as some ant, bee, and termite colonies represent a level of organization intermediate between single organisms and the ecosystem: you can think of them as comprised of individuals whose coordination and integration have reached such a sophisticated level that they function with some of the seamlessness of a human body. The superorganism whose “hand” reaches into your sugar bowl is probably around the size of a large octopus or a garden shrub, and it will have positioned itself so that its vital parts are hidden and sheltered from climatic extremes, while it still has easy access to food and water.
The term “superorganism” was first coined in 1928 by the great American ant expert William Morton Wheeler. Over the ensuing eighty years, as debates around sociobiology and genetics have altered our perspectives, the concept has fallen in and out of favor, and Hölldobler and Wilson’s book is a self-professed and convincing appeal for its revival. Five years in the making, The Superorganism draws on centuries of entomological research, charting much of what we know of the evolution, ecology, and social organization of the ants.
For all its inherent interest to an intelligent lay reader, it’s a technical work filled with complex genetics, chemistry, and entomological jargon such as, for example, “gamergate,” “eclosed,” and “anal trophallaxis.” Occasional lapses add to the lay reader’s difficulties. The etymology of “gamergate” (“married worker”), for example, which is so useful in understanding the term, is given only many pages after it’s first introduced. I fear that The Superorganism may reach a smaller audience than it deserves, which is a great pity, for this is a profoundly important book with immediate relevance for anyone interested in the trends now shaping our own societies.
Ants first evolved around 100 million years ago, and they have since diversified enormously. With 14,000 described species, and perhaps as many still awaiting discovery, they have colonized every habitable continent, and almost every conceivable ecological niche. They vary enormously in size and shape. The smallest are the leptanilline ants, which are so rarely encountered that few entomologists have ever seen one outside of a museum. They are possibly the most primitive ants in existence, and despite being less than a millimeter in length they are formidable hunters. Packs of these Lilliputian creatures swarm through the gaps between soil particles in search of venomous centipedes much larger than themselves, which form their only prey. The largest ant in existence, in contrast, is the bullet ant, Dinoponera quadriceps (of which Hölldobler and Wilson give abundant details, yet frustratingly neglect to inform us precisely how large these formidable-sounding creatures are). Inhabitants of the Neotropics—South and Central America—bullet ants belong to a great group known as the ponerines.
In explaining what a superorganism is, Hölldobler and Wilson draw up a useful set of “functional parallels” between an organism (such as ourselves) and the superorganism that is an ant colony. The individual ants, they say, function like cells in our body, an observation that’s given more piquancy when we realize that, like many of our cells, individual ants are extremely short-lived. Depending upon the species, between 1 and 10 percent of the entire worker population of a colony dies each day, and in some species nearly half of the ants that forage outside the nest die daily. The specialized ant castes—such as workers, soldiers, and queens—correspond, they say, to our organs; and the queen ant, which in some instances never moves, but which can lay twenty eggs every minute for all of her decade-long life, is the equivalent of our gonads.
Pursuing the same reasoning, Hölldobler and Wilson argue that the nests of some ants correspond to the skin and skeleton of other creatures. Some ant nests are so enormous that they are akin to the skeletons of whales. Those of one species of leafcutter ant from South America, for example, can contain nearly two thousand individual chambers, some with a capacity of fifty liters, and they can involve the excavation of forty tons of earth and extend over hundreds of square feet. Coordination within such giant colonies, which can house eight million individual ants, occurs through ant communication systems that are extraordinarily sophisticated and are the equivalent of the human nervous system. Not all ant species have reached this level of organization. Indeed, one of the most successful groups of ants, the ponerines, rarely qualifies for superorganism status.
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’s 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, they are promptly carried off to the ant cemetery by the undertakers, 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 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. 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 depart 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.
Some ant species do not have queen ants in the strict sense. Instead, worker ants (which are all female) that have mated with a male ant become the dominant reproductive individuals. These are the gamergates, or “married workers,” and their sex life can be brutal. In one species the gamergates venture outside of the nest to attract a male, engage him in copulation, then carry him into the nest before snipping off his genitals and throwing away the rest of his body. The severed genitals continue to inseminate the gamergate for up to an hour, after which they too are discarded. The fertilized gamergates then vie for dominance, causing disruptive conflict in the nest. Sometimes an oligarchy of gamergates is established, but in other instances a single gamergate triumphs.
You might think that such an established gamergate would watch the colony carefully for signs of emerging rivals, but this is not the case. Instead it’s the worker ants that do so by taking a keen interest in the sexual status of their sisters. If they sense that one is becoming a sexually active gamergate, they will turn on her, either assaulting her or watching carefully until she produces eggs, which they promptly consume. It’s intriguing that the sterile workers play the role of monitoring and regulating the sexual life of the colony. In a stretch of the imagination, I can see parallels between this behavior and the role of policing and censuring the sex lives of the rich and famous that gossip magazines play in our own society.
The ponerines are the most diverse of all the ant groups, and are global in distribution. They cannot really be thought of as sophisticated superorganisms, however, for they tend to live in small colonies of a few tens to a few thousand individuals, with one Australian species living in colonies of just a dozen. Like Stone Age human hunters who specialized in killing woolly mammoths, the ponerines tend to specialize in hunting one or a few kinds of prey. That the great success of the ponerines is achieved despite their primitive social organization presents entomologists with what is known as the ponerine paradox. It lacks a widely accepted solution, but researchers suspect that it’s the ponerine predilection to seek specialized types of prey that limits their colony size (for such specialized hunters cannot gather enough food to develop large and sophisticated colonies). If this is the case, then the very characteristic that helps the ponerines to diversify and survive in a wide variety of environments also prevents them from attaining superorganism status.
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 tens of 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 like 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.
The fungus farmed by the leafcutter ants grows in underground chambers whose temperature, humidity, and acidity are precisely regulated to optimize its growth. The fungus, which produces a tiny mushroom, grows nowhere else, and genetic studies reveal that various attine ant species have been cultivating the same fungus strain for millions of years. In truth, after tens of millions of years of coevolution such is their interdependence that the ants cannot live without the fungus, nor the fungus without the ants. The system is not perfect, however, for the ants’ fungal gardens are occasionally devastated by pests. One of the worst is an invasive fungus known as Escovopsis, whose depredations can become so severe that the leafcutters must desert their hard-won gardens and start elsewhere anew. Often a colony so beset evicts a smaller attine colony, taking over the premises and enlarging them to suit.
Fortunately, the ants possess a potent defense against this fungal weed that usually prevents its proliferation. Their fungicide is produced by a bacterium that is found only in pits located on specific parts of the ants’ bodies, and that is known to exist nowhere else. These bacteria produce secretions that not only destroy the Escovopsis pest, but promote the growth of the fungus the ants wish to cultivate. 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.
One curious aspect of the agricultural enterprise of the attines is that the worker ants rarely eat the fungus they cultivate. Studies show that the adults gain most of their nutrition from plant sap, deriving a mere 5 percent from fungus. The balance of nutrients in the fungus, as it happens, is poorly suited to the needs of adult ants but is perfect for their growing young. The mushroom gardens are thus cultivated principally for the delectation of the ant larvae. Indeed it forms their only source of food.
When growing fungus on such a large scale, waste management becomes a crucial issue, and the attines have developed a finely tuned solution. Their sanitation teams comprise one group of workers that gathers the refuse from inside the colony and dumps it at depots outside. From there dump managers that work exclusively outside the nest carry the waste to great disposal sites far from the colony. The dump managers that work outside are mostly older ants that have only a short time to live in any case, which is a good thing, for the great refuse dumps they toil at teem with pathogens and toxins. This system effectively quarantines the colony from a dangerous threat and at the same time minimizes worker loss of life. Curiously, humans have found a use for the ant refuse. So strong is the ants’ aversion to it that South American farmers gather it and sprinkle it around young plants they wish to protect from attacks by leafcutters.
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.
This capacity is perhaps most clearly illustrated when an ant colony finds reason to move. Many ants live in cavities in trees or rocks, and the size, temperature, humidity, and precise form and location of the chamber are all critically important to the success of the superorganism. Individual ants appear to size up the suitability of a new cavity using a rule of thumb called Buffon’s needle algorithm. They do this by laying a pheromone trail across the cavity that is unique to that individual ant, then walking about the space for a given period of time. The more often they cross their own trail, the smaller the cavity is.
This yields only a rough measure of the cavity’s size, for some ants using it may choose cavities that are too large, and others will choose cavities that are too small. The cavity deemed most suitable by the majority, however, is likely to be the best. The means employed by the ants to “count votes” for and against a new cavity is the essence of elegance and simplicity, for the cavity visited by the most ants has the strongest pheromone trail leading to it, and it is in following this trail that the superorganism makes its collective decision. The band of sisters thus sets off with a unity of purpose, dragging their gargantuan queen and all their eggs and young to a new home that gives them the greatest chance of a comfortable and successful life.
Reflecting on our own societies when armed with knowledge of the ants as provided in The Superorganism, it’s hard to avoid the conclusion that we are in the process of metamorphosing into the largest, most formidable superorganism of all time. Yet even the creation of a superorganism on this colossal scale is not entirely new, for just thirty years ago another gargantuan superorganism came into existence, and it was the ants that created it. This superorganism is composed of fire ants, and already it covers most of the southern United States. It consists of billions of individuals whose ancestors were accidentally imported from South America to Mobile, Alabama, in the 1930s.
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 Hölldobler 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.
Is it possible, The Superorganism left me wondering, that the invention of the Internet is leading to a similar social evolution of our own species? The proliferation of conflict, much of it prompted by defense of national boundaries, may make us doubt it, but other trends are occurring that give pause for thought. As we strive to avert a global economic disaster or agree on a global treaty to prevent catastrophic climate change, we inevitably build structures that, as with the ants, allow the superorganism to function more efficiently. But of course it’s possible that we’ll fail to make the grade—that our destructive path will catch up with us before we can make the transition to a seamlessly working superorganism.
When conferring an honorary degree upon the man who invented the term “superorganism,” President Lowell of Harvard University said of William Morton Wheeler that he had demonstrated how ants “like human beings can create civilizations without the use of reason.” Create perhaps, but there is no question of maintaining this first global civilization without resort to humanity’s defining faculty. As the twenty-first century progresses we’ll doubtless find ourselves trying to shape our planet-sized nest as carefully as an ant colony does, but the great difference is this: in the case of the human superorganism it will be our intelligence that will guide us. We have to hope that we shall find ourselves living sustainably in a global superorganism whose own self-created intelligence has been bent to the management and the maintenance of its life systems for the greater good of life as a whole.
February 26, 2009