Adventures Among Ants - Mark W. Moffett [142]
Ants don’t break down their social identity into categories the way a person does. The same man can identify himself as an American, as a resident of Illinois and of Chicago, and as a fan of the Bears: one label doesn’t invalidate another. But even the most discriminating ant can only distinguish other individuals by their caste: as queen, soldier, or small worker. Other associations between nestmates—a team carrying food or pinning down an enemy, for example—are temporary and impersonal. Nor is it likely for an ant to show an allegiance to a particular site or group of nestmates within a colony. In one study, Argentine ants were marked with a radioactive tracer and then allowed to disperse; within three days, the workers had spread outward to other nests at least 40 meters away.12 That’s a lot of “ant miles” they put between themselves.
Despite the ants’ intermixing and flexibility in accommodating new odors, it is possible that the vast extent of a supercolony can mean differences in communication signals, leading to a breakdown in colonymate recognition. The mixture of scent signals used at one location might not apply elsewhere in the colony, for example. Local changes that affect the signals may arise by mutation, random shifts in gene frequency, or crossbreeding, as males fly in from other colonies to mate. The short-lived colonies of other species are unlikely to display genetic variability from place to place (residents can easily walk through the full territory of a colony, blending the population). But a supercolony has decades to accumulate genetic novelties, and because they spread slowly relative to the size of its territory, they will be limited to a particular area.13 The spread is further inhibited by the fact that reproductive Argentine ants disperse little: queens stay in their birth colony and travel only on foot, while males are weak fliers and are usually killed if they land in another colony. These factors lead to inbreeding and result in regions of a supercolony becoming genetically distinct, as is the case within the Very Large Colony.14
Would the Very Large Colony fall apart if a genetic change altered the scent signals its members use to recognize each other? Not necessarily. Suppose that the gene affecting the colony’s odor mutated in a queen. If this signal disrupted the colony identity, the workers in her birth nest would kill her, and the mutation would die with her. But if the mutation were subtle, she and her offspring would survive, and the colony would thereby incorporate the modest new aroma into its identity.
With discrete sites within a supercolony accumulating numbers of such small variations, we might expect ants from distant parts of the same supercolony to fight after being accidentally transported between suburbs in a rosebush or tossed together in a research tub.15 Yet surprisingly, no such overt hostility has been recorded.16 Researchers have brought together workers from hundreds of miles apart within the range of the Very Large Colony, from San Francisco and San Diego, and the ants accept their sisters-in-arms after taking at most a second to inspect them. Such perfect camaraderie amazes me. Argentine ants direct their aggression entirely toward outsiders, and none whatever toward their billions of colonymates.17 Their smoothly run societies make ours, marred by meddling, sharp differences of opinion, cheating, selfishness, outright aggression, and occasional homicides, look positively dysfunctional. As frequent New Yorker contributor Clarence Day put it in 1920: “In a civilization of super-ants or bees there would have been no problem of the hungry unemployed, no poverty, no unstable government, no riots, no strikes for short hours, no derision of eugenics, no thieves, perhaps no crime at all.”18
SOCIETIES WITHOUT END
The groups of Argentine ants that first arrived in the southeastern United States and, later, in California were each at most a few queens and workers from one colony. “It would be as if all of the people in the United States were descended from