AMONG THE MORE than fifteen thousand species of ants classified by entomologists, there exists a babble of tongues, each a Formic,† an array of pheromones used by workers to order their social life. Other biologists and I have discovered in part how to translate their chemical language into the audiovisual languages of human beings.
So, how many pheromones does a worker of a given species use? How many words exist in what I hope I may be permitted to call a “formicese”? My guess is somewhere between ten and twenty, the exact amount according to species. In addition, ants are able to create new messages by varying the amount of the pheromone released.
For example, when a harvester ant (Pogonomyrmex badius) trying to collect seeds and other food is confronted by a pack of fire ants, its deadly enemy, it spritzes a fine spray of the alarm substance methyl heptanone from twin glands at the junctures of its sawtoothed mandibles. The material is volatile, so it dissipates rapidly to produce an odor easily detected by ants, and people. Unless the ant then runs away, the methyl heptanone vapor forms a hemispheric “active space,” within which the pheromone can be smelled, by ant or human. The substance, hence the odor, is greatest at the point of release on the front of the ant’s head. It weakens exponentially toward the boundary of the active space.
The result of speech achieved by smell is that when first detected by the “listening” ant at the edge of the active space, the signal is weakest. A weak signal serves to attract the receiver and guide it toward a higher concentration of the pheromone vapor. The methyl heptanone is comparable to a flickering red light; it says, Attention! Something is wrong. Come here and check it out. As the ant moves toward the source and into a higher concentration of the pheromone, it becomes excited and begins to run around in search of the trouble. Help. A nestmate is in a struggle. Run to her, into the higher concentration. Soon, usually within a few seconds, the follower ant arrives at her distressed nestmate and joins the fray. From one pheromone, the harvester ant has fashioned the equivalent of three words.
Can one ant species actually “read” the pheromone language of another? In some cases they can, and the capacity to do so opens the door to their victimization by social parasitism. One example I discovered in the mountain forests of northern Trinidad involved the arboreal species Azteca chartifex. The colonies, which grow to immense size, build massive nests of masticated wood fiber. Tens of thousands of workers stream outward in thick marching columns along the tree branches and down the trunks to forage on the rich plant material and insect populations that inhabit the ground vegetation.
While visiting a nature reserve in the mountains of northern Trinidad, I noticed that a second kind of ant, somewhat larger and differently colored (later identified as Camponotus apicalis), was running with the Azteca. They were following the Azteca trails out of their own nest in the tree down to the feeding area on the ground. In effect, the Camponotus were using information stolen from the Azteca to appropriate part of the Azteca food supply. The Azteca tried to catch the Camponotus, but the intruders were too strong and fast to be trapped and pinned.
Ants are geniuses of olfaction. Dogs have an almost unlimited capacity to distinguish odors, but no more than ants, which know better what to do with them. Ants have built civilizations upon odors to which their brains are genetically designed to respond. Humans do better with sounds and visual signals—words—given arbitrary meanings that can be pieced together with sentences, yielding thereby a vastly larger potential array of meanings.
Ants, for example, can put together pheromones with other odors to create “proto-sentences.” A foraging worker, having encountered fire ants, rushes into its home nest with the equivalent of shouting Emergency, danger by spraying alarm pheromones, then Enemies by presenting the odor of fire ants it has acquired on its integument during a recent tussle, and then This way, follow me, as it turns and runs back along the odor trail it has just laid. I can imagine another pheromone in the air implicit to those who go forth in battle: The Queen! the Queen! Fight to the death for our Queen!
Might the ants, as well, during their 150-million-year evolution by thousands of species, have evolved a true language? Can they emit pulses of pheromones varying in frequency or amplitude to create words, as we do so well using sound? The answer, established by models from mathematical physics, is maybe, but highly improbable. Odor pulses are fundamentally different from sound pulses. In generating information—to talk with odor, so to speak—it would be necessary to control the emission and reception over a distance of only a few millimeters.
Ants and other invertebrate animals are too small, and their brains too meager, to inch past the limits of communication which they possess. Even so, social insects in general, and ants in particular, have, somewhere among the thousands of living species, accomplished almost every other innovation with chemical communication that we are able to imagine.
† “Formic” is the name Robert Frost used for ant language in his splendid little poem “Departmental.”