Summer World_ A Season of Bounty - Bernd Heinrich [88]
On 11 August a column of red ants traveled to the same distant north colony as the previous summer, and I took some notes while watching their trail. During a ten-minute period I saw ninety-one red ants pass by carrying ant brood (six large larvae or ant grubs and eighty-five pupae), and forty-seven were carrying adult black ants. As before, there was no hint of a struggle; each of the captive black ants seemed to tuck itself into a little ball, the better to be carried.
The carriers were not significantly slowed. Unloaded ants were passing at an average pace of 1.9 inches per second, whereas those carrying another ant were running at 1.7 inches per second. The apparent captives held still for the entire time—approximately half an hour—required for them to be carried the total distance of 250 feet from their nest. Before, I had seldom seen an ant stand still for even a few seconds. Were they drugged? To find out, I caught pairs and released several captives from the grip of their red captors, and these instantly ran off as fast as ants run. They were obviously in great shape. Why did they never run off on their own?
The multi-day raid (as I took it to be) always stopped in the evening and resumed late the next morning. This pattern continued for five days, and I started to notice other odd details. Occasionally, a black ant carried another black one, and then—even more puzzling to me—I saw a black ant carrying a red one. (The two differently colored ants were Formica subintegra, the red; and F. fusca, the black). I didn’t know what the anomalous behavior meant, but I brushed it off as typical ant confusion, rather than ignorance on my part.
Strangely, I saw no battles at the raided nest. I did see one red ant tussle with a black ant, but the latter turned belly up surprisingly quickly and then submitted to the tuck position so it could be carried away. Would it have been killed if it had resisted?
Hoping to get to the bottom of the ants’ strange behavior, I finally dug into the red ants’ nest where the blacks were being deposited. To my now ever-increasing surprise it didn’t look much like a red ant mound at all. In fact, inside this nest the blacks outnumbered the reds. In a random count, I tallied 178 blacks and only 23 reds. Was this actually a black colony rather than a red colony? Five days later I was again watching the continuing drama as large numbers of reds left their fortress to hit the trail and head north. I counted fifty-six reds carrying blacks, seven reds carrying reds, and one black carrying a red. So, proportionally at least, the reds were the main carriers. Along the same ant column I saw two black queens being pinned down by six to ten red ants each. The next day (17 August 1982) the raided mound was nearly empty. But in the morning the knot of reds were still pinning down a black queen (the same one?) on the trail at the same spot where they had been holding one yesterday. And by early afternoon that queen was still being held by a mob of about fifty reds. Why didn’t they kill her?
I surveyed the ant mounds in the clearing around our shack, and then also at a larger clearing nearby where we were building a log cabin. I found that the reds were in the minority: thirty-nine of forty-one colonies were populated exclusively by blacks. The reds were not just raiders; they had other professions as well: fifteen of seventeen aphid colonies on young poplar saplings were tended by them, and I found only two of the blacks. Additionally, both kinds of ants tended little green nubs that looked like aphids, on the petioles of new chokecherry leaves. The ants must have been getting some secretion from these