Adventures Among Ants - Mark W. Moffett [51]
Seeking moist ground, we left the path within an hour to search the taller gallery forests along a stream. Soon we were joined by chimpanzee expert Andy Fowler, a soft-spoken Englishman with a dependable wry smile, and Darren Ellis, a thin, bespectacled American, who began a dialogue with Caspar that continued nonstop for three weeks as they hammered out the protocols Darren would use for his master’s thesis. He was studying the stick tools made by chimps, the driver ant’s response to the tools, and the importance of these army ants to the chimp diet. This last topic required that Darren count the ant parts in any chimp dung he could find—a task that turned out to be even less pleasant than it sounded.
Andy led us to a driver ant nest he’d spotted two days earlier. From the base of a toppled-over kapok tree spilled pyramids of soil that extended into a streambed. We saw some old, weak, and wounded individuals withdrawing to the garbage heap to expire. Some were being captured by workers of a black-and-coffee-colored acrobat ant, who were waving their heart-shaped abdomens in excitement at the easy repast. Bagging vulnerable workers in the trash piles or the wounded left behind after an army ant raid is an industry for certain ant species.
This driver ant was Dorylus rubellus. As I watched their dead and dying, I thought of how my mentor, Edward O. Wilson, had figured out how ants recognize their deceased kin. In 1958, working at Harvard, Ed and two colleagues proffered ants squares of paper soaked with a series of foul chemicals associated with decay. One compound, oleic acid, yielded a full-blown necrophoric response, inciting workers to haul the paper to the trash pile. When the researchers daubed oleic acid on a live ant, her determined nestmates dragged her off as well. Until she licked herself clean, the unfortunate individual was repeatedly thrown back onto the midden with every attempt to enter the nest.5 Smell like the dead, and dead you must be.
Searching along the streambed, I found the driver ants’ trail, which was exposed for 3 meters before it climbed an embankment and disappeared into the forest. A few workers were carrying chunks of insects, probably collected in a raid deep in the forest, slung under their bodies in classic army ant style. What I saw next caused me to drop to my knees. The drivers looked and behaved so familiarly that it was easy for me to believe I was in Asia again watching a stream of marauder ants. Part of the reason was the posture of the guards, who stood or strolled near the trail in marauder ant fashion, high on their legs, with raised heads and open mandibles.
I soon spotted differences from the marauder, though. An inordinate number of medium and large driver ants, rather than the small workers, had taken guard roles. The traffic on the trail also seemed chaotic, seldom sorting itself into lanes. Contrary to some descriptions I had read, the ants ran side by side with their feet on the ground, not atop one another. Workers stepped on those next to them, however, and big ones strolled over small ones—common practice in polymorphic species, preventing traffic snarls behind workers that come to a sudden halt.
On portions of the route, the guards interlinked in a way I had never seen before: hooking their clawed feet together like some horror-film version of armored cheerleaders forming a pyramid, they welded a lattice over the traffic below them in a defensive shield bristling with jaws. Unlike marauder ants, driver ants have no eyes, and all their joint activities are truly examples of the blind leading the blind.