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.