Adventures Among Ants - Mark W. Moffett [101]
All this action was happening one late afternoon at Sagehen Creek Field Station, on the eastern slope of the Sierra Nevada north of Lake Tahoe. Starker Leopold, son of the renowned conservationist Aldo Leopold, established Sagehen on U.S. Forest Service land in 1951. The rolling hills below a robin’s-egg blue sky were sprinkled with lodgepole and Jeffrey pines. It was mid-July, the raiding season for the Amazon ants in this region.
If this had been an army ant raid, the column would likely have continued to advance while part of the workforce stayed behind to attack the nest. But instead the entire Amazon regiment had come to a halt, targeting this locale. While the charge was still under way, the Amazons started to ferry hundreds of pupae and a few larvae homeward in ragged formation, and within minutes the looting operation began to close down. Alex and I followed a long, unbroken caravan back to the road where we had first come upon the more tight-knit advancing platoon. From there, the returning column stretched an additional 50 meters until it headed below-ground, into its own nest, where I again saw scattered silver-black Formica workers. Although they looked identical to the ones the Amazon workers had just raided, these individuals were, in fact, Amazon slaves.
What I saw next sent a shiver down my spine. When a Formica slave encountered a returning Amazon, she tugged at the pupa the Polyergus held. The Amazon relinquished her grip, allowing the Formica to take from her the Formica just stolen from its nest. Other Formica slaves, not occupied in hoisting pupae, were actually moving slavemakers: tired out, I imagined, by the conquest or the long journey home, some Polyergus were allowing themselves to be carried the last leg of the trip. Normally this form of adult transport is associated with novice workers being relocated during nest migrations, not with adult warriors fully able to get around on their own. But here the enslaved Formica workers were transporting the victorious slavemakers as if they were royalty curled up comfortably in their palanquins.
For the average Amazon ant, the royal treatment continues after she arrives home. Entering the nest, she lounges around, at most grooming herself or her nestmates, while the Formica slaves tend to her needs. Her daily efforts last for a couple of hours at most. Yet Alex told me only about half the slavemakers are likely to go on a raid; the rest stay behind, doing nothing all day. For a booming society of several thousand ants the tempo of life is abnormally laid-back for Polyergus breviceps. (To our way of thinking, the average ant worker’s life sounds like slavery even when she is in her birth nest, though in that case she is at least toiling for the benefit of her mother, the queen.)
That afternoon’s confrontation at the Formica nest was a soundless blur lasting twenty minutes, more or less the normal length of such a slave raid attack. The timing was typical too: conducting their raids late in the day, Polyergus is forced to get the job done and head home before the sun wanes, since they don’t stay out after dark. It is unclear why the raiders don’t give themselves more time by beginning earlier. Perhaps the delicate pupae would cook if trundled away in the midday sun. Or perhaps as the afternoon cools the Formica ants fetch brood from deep in the nest to warm nursery chambers near the surface, and so the slavemakers don’t have to