of a marauder ant raid, though it’s less methodical and more dispersive than cohesive.22 A forager who detects wood at a distance, likely by scent, will abandon its search and move straight to the food. Usually she explores the wood alone, then lays a recruitment trail back to the nest. Being defenseless and easily dehydrated, termites expire fast when lost. Staying in the columnar networks helps them find their way back home and hastens the construction of the galleries the termites require to survive on exposed ground.
Another vegetarian engages in mass hunts that have a protective as well as a nutritive function. Whereas an unaccompanied eastern tent caterpillar can easily lose its grip on a tree, several together will lay a silk mat that engages their feet and keeps them from falling. These leaf eaters then find meals in a procession, with the pioneers pushing ahead short distances before retreating, to be replaced by the ones behind.23 A group can follow an old silk trail or strike out over new terrain. A lone caterpillar finding satisfactory greenery will lay an especially attractive—perhaps chemically stronger—recruitment trail back to the silk tent housing the colony, in some cases drawing out the entire population.
This is where all other animals that search for food in groups differ from ants like the marauder: whether caterpillar or bird, bacterium or wolf, individuals are fully capable of moving away from the pack or flock and foraging without companions. And with rare exceptions, “alone” in these species really means alone, because few animals have the capacity to recruit assistants from a distance. A few birds and primates call one another to food: for example, in Africa chimpanzees draw others to bonanzas of fruit in trees by uttering loud hoots, and pied babblers lead their novice fledgling offspring to feeding spots with a “purr” sound.24 But such social actions are virtually unknown in most species, where signals such as the yelp of the coyote or the singing of whales more often function in maintaining appropriate spacing between individuals, in combat, courtship, or group bonding, or to keep pack members together when they are on the hunt, than in calling in the troops.
One rare exception is the naked mole rat, an African rodent with antlike colonies that include queen, small worker, and soldier castes. The worker rodents lay odor trails to the root tubers their colonies feed upon.25 Another remarkable exception, involving a symbiosis between animals who have little in common, is the raven, who will call out to guide wolves to prey; the wolves share the prey with the ravens after the kill.26
COMPARATIVE MARTIAL ARTS
Even though marauder and army ant campaigns are directed at predation rather than military conquest, the byzantine structure of their pillaging and the frequency with which they do battle with other ants make it tempting to conceive of their “armies” in martial terms. Predation and combat have been linked in human history as well, the tools for one often serving handily for the other, with battles occasionally ending in cannibalism.27
Swarm raids compare neatly to the deployment of Roman heavy infantry and other early battalions that swept forward in a broad front. One Roman innovation was to spread troops a bit more widely than did previous armies, which gave each man a few square meters in which to defend himself. Though their workers are never far apart, marauder and army ants similarly tend to remain a few body lengths away from each other, right up to the front lines, a spacing most likely maintained by the ants in order to avoid treading on one another.28
Naturally, there are differences between the Roman armies and ant armies. Roman troops fell into formation only in times of active conflict, when soldiers on the front lines served as a defensive shield against another army open to view, protecting the soldiers behind them and slowing the advance of the opposing army before them. Among marauder and army ants, in contrast, the foremost workers serve as a contiguous search party to flush out prey. Rarely are the ants’ opponents arranged in a similar configuration; rather, they are discovered and overtaken in sporadic fights.
Despite their tactical responsiveness to prey, marauder raids can seem regimented when compared to the flexibility of Roman legions. Deployed in formations arrayed three deep, the Roman troops could be reconfigured in response to changes in an enemy’s assault. The phalanx might be preceded by cavalry that harried the enemy in advance, for example, or by scouts sent ahead to report on the lay of the land so that the day’s plan could be adjusted accordingly.
My painstaking observations of the marauder ant raids left me with several unanswered questions. Animals as diverse as wolves, birds, and bacteria are able to mass forage in organized groups and then to move off in isolation. Why aren’t marauder ants and army ants similarly able to employ long-distance scouts to assist in their concentrated raids? The risks a marauder or army ant scout might face would seem to be no different from those encountered by any kind of ant that searches on her own, entering a hostile world without backup. Wouldn’t the rewards, for the group, far outweigh the risk to the individual?
Perhaps risk has little to do with it. Watching the marauder ants cart off fruit, seeds, and animal prey, I suspected that the unpredictable quality of their plunder simply made such reconnaissance pointless. Or maybe any tendency for an individual ant to scope out her surroundings—and in so doing wander off on her own—somehow interferes with the mass-foraging process, in which a total fixation on tracking the pheromones of the group is key.
Humans are accustomed to supervision and chains of command that encompass every level from presidents to petty administrators. Roman soldiers wheeled and charged under the direction of officers moving through the ranks. For certain ants, too, transient leadership roles do exist, in some circumstances—as with the successful Leptogenys scout I observed in India, who always stayed with the assembled troops, guiding them to the termites she found. What, then, of the leadership role of individuals in a marauder ant raid?
Once, at the Botanic Gardens, I attempted the near impossible: to follow an individual marauder minor worker entering a swarm raid. I picked her out because she was missing the end of one antenna. It was too difficult to focus binoculars on her, so I tied fabric from an old T-shirt across my face to keep my breath from disturbing the ants and got in close. I followed “Stumpy” for a minute through the tributaries of workers in the raid fan. She dashed wildly for a moment near the commotion of ants on a beetle larva—agitated, I surmised, by alarm pheromones released from the poison glands of the struggling workers—then kept going. Approaching the raid front, she wandered and finally entered a stream of ants, where I lost her.
Nowhere along her route did I observe other individuals guiding her, or her influencing other workers. As with army ants, the marauder ant is a species with no established leaders. If I could communicate “take me to your leader” to one of them, it’s unlikely I would be shown the queen, who, like all ant queens, lays eggs but coordinates nothing. Nor does any of her workers inspire, cajole, or force the whole army to take a line of action. Proverbs 6:6–8 makes this point: we must “go to the ant” and “consider her ways, and be wise” because she does the job without “guide, overseer, or ruler.” King Solomon must have been a devoted ant observer to reach this conclusion. In all likelihood, he grew up watching Messor barbarus, the dominant seed harvester of the Mediterranean, which indeed “gathers her food for the harvest,” as the Bible tells us.
The hardworking ant described by King Solomon was likely a solitary-foraging seed harvester ant such as this Messor barbarus from the Kerman region of Iran.
A century ago, Harvard’s erudite ant scholar William Morton Wheeler called army ants “the Huns and Tartars of the insect world.”29 But no myrmecologist has ever identified a Genghis Khan or Attila among them. At best, an individual in the raid may be momentarily better informed than others, giving her a brief and local influence.30 That could happen when a worker at the front sends out recruitment signals to prey—but even then she is likely to be acting in concert with nearby sisters. No
