Adventures among Ants. Mark W. Moffett

ground, so taking this course may be a matter of chance. If the prey fails to chose the right direction, the army will advance to its new location and strike again. And if it escapes once more, a swarm may try a third time, or more. Because of their width, swarm raids are most likely to repeatedly contact the flipping worm or leaping grasshopper. (A narrow column raid is different; its net is too narrow and weak, and most victims break free. The ants in column raids therefore reap mostly seeds and frail prey, though the raid may burgeon into a swarm if they find bigger spoils.)

      Minor workers at the front of a marauder ant raid in Singapore being cut to pieces while subduing a termite soldier.

      A major worker crushing the termite after the minors pinned it down.

      Even escapees may not survive. I once saw a cricket rocket from its hiding place beneath a leaf. In a series of zigzag moves it ended up far from the raid, but a few ants still clung to it stubbornly. Their gnawing slowed it down, until at last its body convulsed. However, the ants that subdued it were now so far from their colony that they would die before ever finding their nest again.

      Participants in a marauder raid seem to be forever in battle mode. They fight with a dogged precision that is chilling, and in large raids there certainly seem to be troops to spare. The minors show by far the highest casualties. The bounding cricket managed to chew a couple of the minors on its leg to a pulp before succumbing to the rest. On my way back to the raid, I saw minor workers puncturing a plump caterpillar, and one drowned in the jelly that oozed from it. Later on in that raid I saw a termite soldier with a burnished red head that dwarfed the minor workers surrounding her like a grizzly bear cornered by dogs. The termite’s black jaws were sharp as knives, and each minor that came near was sliced apart as cleanly as if by a guillotine, until a dozen ants stormed her hindquarters and brought her down.

      Like a war correspondent inured to tragedy, I watched hundreds of minors being sundered and smashed in struggles with prey, the horror of the slaughter magnified through my camera lens. By never straying from the task to save themselves, they displayed breathtaking devotion to their duty. It made me wonder about the advantage of psychological numbness in combat even among sentient humans. As one author wrote of the Civil War, “Soldiers perhaps found it a relief to think of themselves not as men but as machines.”⁶

      Such thoughts reflect how caught up I was in the drama of the moment, pressing the button of my camera each time a surprising event happened. I saw that the minor workers were able to stretch the legs of the termite soldier until she was spread-eagled (click). By this time, the raid front had advanced beyond the victim, who was now deep within the swarm. Here the media and major workers roamed in numbers (click). The large ants were as plucky as the minors, and they had the size and mandibular power to be worthy of the designation “soldier”; but by dint of their location, most of them joined the fray at the termite only after the prey was felled (click).

      My images transferred onto a storyboard that showed that inside the raid, after the minor workers immobilized the body, the medias and majors were a strike force that moved in to inflict what carnage they could. Small media workers fit into tighter nooks and crannies than the majors can reach, perhaps yielding a kind of division of labor in destruction.

      The allocation of effort between the minors, which restrain prey, and the medias and majors, which smash it, is related to their respective locations within the phalanx. It’s unlikely that special communications are used to get ants to these positions; instead, the minors reach the front lines first because they walk more nimbly than their larger sisters, while the larger ants are waylaid by their duty to crush prey farther back in the raid. Regardless, the role of minors at the front lines is clear. Only they and a few small medias secrete trail pheromones, testament to their importance in moving the raid ahead and summoning others to prey.

      To a military historian, the marauder ant strategy evinces a classic use of personnel. Placing large numbers of abundant and expendable weak individuals in jeopardy at the front lines not only increases the catch but also minimizes the loss to the society overall. The Romans used a similar strategy at their battlefronts: instead of drawing from highly trained city dwellers, they largely conscripted farmers, who were available in droves and could be replaced at little social cost—a practice that continued at least into medieval times, when poorly trained men were, literally, used as cannon fodder.⁷

      The minors’ bold actions assure few large warriors being sacrificed, a sensible outcome given the expense of raising majors that can weigh hundreds of times as much as one minor. In a sense, the medias and majors are equivalent to the human warrior elite—physically stronger, superior fighters, often positioned behind the relatively inefficient front-line rabble. The human elite are provided with better weapons and training and protected by the most expensive armor, as tough as a soldier ant’s exoskeleton.

      The large workers are attracted to a prey’s flailing extremities and dutifully hack off every moving leg and antenna. With the prey rendered powerless, unless its shape is awkward (like that of a praying mantis, which the ants will tear apart), the minors heft its body back in one piece. I once saw the ants retrieving a limbless gecko, which clued me in that they had taken it alive.

      Dismemberment immobilizes but doesn’t necessarily kill. Moving animal prey to the safety of the nest before the coup de grâce may reduce the chance of its being stolen by competitors or washed away in a storm. By keeping prey alive, the ants may also be able to preserve their meat (something that ants with stingers do by paralyzing their victims).⁸ I learned of this strategy one day at the Botanic Gardens when I snatched a limbless katydid from marauders on the way to their nest. I put it in a jar and forgot about it until, two days later, I noticed its leg stubs still writhing. That night I dreamed I was that katydid, being helplessly transported to the bowels of the nest, to be digested at the ants’ convenience by the protein-hungry larvae.

      SPRINGTAILS

      Marauder ants conduct raids to catch tough prey, but mass foraging helps them obtain other kinds of meals as well. The poorly armored minors, though not intimidating, are agile and have good vision. I’ve watched hundreds of them retrieve speck-sized jumpers called springtails.

      Springtails are the rabbits of the insect world—fast breeding, abundant, and prodigiously jumpy. As the name implies, they use their tails as a spring. If one senses a threat, its tail, or furcula, normally folded under the body, snaps downward, launching the insect through the air.

      Before exploring the marauder ant’s tactics for capturing these motile creatures, let’s first look at a very different approach. A speck herself, a burnished red Acanthognathus teledectus ant moves stealthily through the forest litter in Costa Rica, her long, pitchfork-shaped mandibles held straight to each side. Coming on a springtail, she slows to a glacial creep until two long hairs extending from her mandibles touch the quarry, indicating that her distance is perfect. Her jaws snap forward; their prong tips puncture the springtail and hold it tight. Quickly now, the ant slings her hind end under her body and incapacitates the prey with an injection of toxins through her sting, after which she hefts it overhead and carries it home.⁹

      With blows from her mandibles, an Acanthognathus trapjaw worker in Costa Rica repels a pseudoscorpion from the tiny hollow twig occupied by her colony. Behind her, a larva feeds on a springtail.

      Acanthognathus displays the special skills required for solitary-foraging species to snare these speed demons. Success among springtail-hunting virtuosos depends on stealth and the use of mandibles as an unusual tool. Devices such as trap jaws and stingers are especially common among species with small colonies with only one kind of worker, such as Acanthognathus, whose workers so often need to act alone. Unlike with the antlers of moose or the tusks of elephants, their function is not to impress but to kill and butcher.

      “Trapjaw ants” like Acanthognathus have