Adventures Among Ants - Mark W. Moffett [55]
While there may be something to this hypothesis for many aspects of colonial life, keeping such a vast labor pool in constant motion makes no sense as a way to run a business—or an ant raid. Perhaps the structure and momentum of a raid are somehow sustained by the manner in which the ants cycle between the nest and the raid front as an unbroken part of the superorganism. It may be that the incessant long hauls between raid and nest are a by-product of this dynamic, with which, in much the way humans have retained their (now useless) wisdom teeth, the ants have been unable to dispense.
RAIDING A NEST
Day after day, Caspar and I explored the terrain for driver ants, but at night the convenience of the dining room colony was irresistible. I’d eat yam tubers and ground cassava on the porch with my companions while gazing at the tree with the driver ant nest. With the monkeys asleep, the primatologists’ fieldwork was over for the day. Ours, however, had just begun. Each night after feeding and watering ourselves, Team Ant would scoot over to check out rubellus in action.
On my second night at the field station, the colony raided away from the dining room, into an expanse of savanna extending along the station’s border. This raid contained far more big workers, about the size of a marauder ant major but without their boxy heads, than the one the night before. I had no idea why. Could the ants adjust their work crews according to some labor need I couldn’t perceive?
Stepping into the 2-meter-tall grass, I worried about not seeing the bloodthirsty ants before they saw me. (Army ant studies invariably suffer from a variation of the Heisenberg Uncertainty Principle: an observer may influence a raid simply by agitating the subjects with the slightest disturbance. If only myrmecologists could concoct an antigravity device that allowed them to hover over a colony without touching anything, not to mention an oxygen tank to keep them from breathing on the ants. I’d order the deluxe unit, with a personal air conditioner, because the ants don’t appreciate sweat dripping onto them, either.) Fortunately, I soon found that I could watch these ants without their noticing because there were workers swiftly ascending grass stalks directly in my line of sight. With this early-warning system, I was able to stop walking and survey the ground before the more slowly progressing ants in the dense thicket there began to ambush my feet.
Then I noticed that the rubellus were driving carpenter ants, each one clutching a larva or a pupa, up to the tips of the stalks, where they froze. Because of the paltry space on a blade, as few as two or three driver ants were spread out behind the carpenter ants on a meter’s length of stem. It looked as if each driver ant was pursuing the carpenter ants on her own, beyond the raid front, perhaps (given the ants’ blindness) by using vibrations or chemical signals. As I scribbled in my notebook, a driver ant tackled the carpenter ant at the tip of one stalk. Both fell in a tangle into the maelstrom below, where the carpenter ant’s pupa was snatched away and her head torn off before she was buried in driver ants.
Tracking an individual driver ant in the welter of a swarm is well-nigh impossible, which made the action on the blades of grass a great opportunity for me. I watched intently as one carpenter ant after another met the same fate. (As one friend pointed out, it’s cruelly ironic that the most popular product for killing ants is called Raid. Talk about living by the sword, dying by the sword.)
In a desperate gambit, a carpenter ant retreats up a grass stalk with a pupa as driver ants raid the ground below in Gashaka, Nigeria.
Rooting in the earth, I located the carpenters’ nest entrance. Driver ants were emerging