Adventures Among Ants - Mark W. Moffett [37]
Bulwarks constructed over trails and provisions prevent battles among competing marauder ant colonies as well. Where they are absent, combat can last a day and engage thousands of minor workers, which pour along the line of contact between the armies. Sometimes the tangle of ants stretches a meter wide. Compared to the free-for-alls that erupt during prey capture, the fights unfold with extreme care. At first the minor workers examine each other more like dancers than combatants. Brawls begin when pairs interlock mandibles, then grapple for several minutes before disengaging and maneuvering for better position. Fatalities escalate as additional workers pull on one of the locked ants. Fighters can tuck their hind ends beneath their trunks, making it difficult for others to grasp them at their fragile waists. Meanwhile they wave their abdomens in an action called stridulation, in which a ridged surface like a nail file on the undersurface of their abdomen rubs against a scraper located below their slender waist to produce a rasp like the sound made by strumming a comb; it is barely audible when a large worker is squeezed lightly and held up to the ear. This may be a call for help, though ants, being deaf, detect the rasps only as vibrations through the substrate. After some minutes of struggle, one of the ant’s limbs will pop off like the arm of a medieval torture victim stretched on the rack. Slowly, surely, the workers pull each other apart.
Among ants in general, most lethal fights are variants on this hand-to-hand combat. Some species avoid prolonged tussles, instead taking a hit-and-run approach, inflicting damage fast and then dashing away. Many of these use a sort of chemical mace, spraying insecticides from their abdomens. Otherwise ants have not developed techniques to safely inflict damage from a distance—a development in human conflict that began with the invention of the spear. In one remarkable exception, workers from cone ant colonies stop their opponents from foraging by surrounding the enemy nest and dropping stones down the entrance and onto their heads as they attempt to leave, a nonlethal, but effective, technique.8
Which marauder ant colony wins? One especially sizzling afternoon in the Singapore Botanic Gardens I conducted an experiment with bottles of spray paint. By spritzing a different neon color lightly on the traffic moving along the trunk trail, I was able to mark a small portion of several colonies’ worker populations. Three days later I came upon a battle between two of the nests. Scanning the thousands of grappling ants, I watched as the pink colony’s larger battalion eventually swamped the greens, which retreated. With only a hundred casualties on both sides, there was no further commotion. In fights between honeypot ant nests in Arizona, special “reconnaissance workers” move through the battlefield to assess the size of the opposing armies, then draw out more troops or organize a hasty retreat depending on the situation.9 I have no idea if that’s how the greens “knew” to give up—that the odds were against them. But at some point, the green army clearly decided to leave the field of battle rather than fight on.
Because marauder ants lack scouts that could monitor intrusions around their nest, conflicts among them have little to do with territoriality—the control of land. Fights occur only by accident, when one colony’s raid contacts the raid or exposed trail of another, and may be avoided, even near a foreign nest, when trails are sealed over. Because the size of a marauder ant army is likely to increase the closer the battle is to its nest or to the food it is defending, the colony with the most at stake usually swamps the other and wins.
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