Adventures Among Ants - Mark W. Moffett [40]
The painful bites and Thai curses were forgotten once I had tallied the data and gone to relax in the hostel’s dirt-floored canteen, where I ate sticky rice under a ten-watt bulb while trying to impress two girls, on holiday from Australia, with how cool it was to be an entomologist (and when that didn’t work, a National Geographic photographer). But I’d forgotten one of the most important lessons of marauder ant research: one worker always stays behind, after a skirmish, waiting for the proper moment to exact revenge. This time it happened midway through my meal. I started to howl and slap myself, and the girls disappeared.
BREAKING CAMP
Marauder ants are often on the move, and it is here that their roadways again play a role. I have come across dozens of migrations in which the whole society relocates, using the trunk trail for its exodus. Such operations are vaster than any raid. Colony members that normally wouldn’t venture from the nest—every egg, larva, and pupa, every swollen and cowering replete, every delicate callow worker—join a caravan that proceeds as far as 80 meters to a new nest site. The enterprise involves a staggering protective force of workers exploring almost to the span of my hand from the trail flanks. Two to six nights are required, with the convoy taking a break during daylight hours.
Only once have I seen the queen in a migration, and that was in the Malayan species Pheidologeton silenus, which is similar in many ways to P. diversus, the marauder ant. It was near midnight. I had been sitting for six hours in a particularly water-saturated corner of dense rainforest at Gombak Field Station in peninsular Malaysia, watching ants hauling their brood. Suddenly, there she was, part of the convoy, marching along with her stout body and strong legs as if she were designed for a life on the run. Escorting her was a tight retinue of several hundred minor workers. Some of them rode on her body; others ran in a mass a couple of inches ahead and behind her and on each side. The emigration column swelled as she passed, with the entourage flowing at exactly her pace. So quickly I had no time to pull out my camera, she disappeared where the trail led into the dripping brush.
Why move? Changing house can be a time-consuming chore. The honeypot ants of the southwestern United States, who laboriously carve nest chambers into tough desert clays, seem to never move: perhaps their expenditures on home construction are too high. For others, migrations occur only after a dire circumstance, such as the flooding of the nest or attacks by a vertebrate predator. But with the marauder, when I expected a migration to occur, it often didn’t, and vice versa. I documented migrations of colonies that were eating well (in one case, dining on daily servings of bird seed supplied by me) but then inexplicably moved to a barren area. Conversely, colonies often stayed put even after I had dug up part of the nest for study.
The frequency of marauder colony migrations remains a mystery. My best guess is that colonies move a few times a year on average, but because I couldn’t watch colonies around the clock, I could not be sure the colony at a site was the same or had changed since I had last been there. Several times after observing one colony migrate, for instance, I saw another move into its abandoned nest, which made me wonder if the ant colonies were like human families upgrading their homes. One colony moved 8 meters and then two weeks later relocated to its original location.11
Similar to marauder ants, though at the opposite extreme from homebody honeypot ants, are the nomadic army ants, which have been characterized as unique for the frequency, predictability, and organization of their migrations. Describing the transient domiciles of African army ants, the Reverend Thomas Savage reminded his readers in 1847 that “a man’s dwelling indicates the nature of his employment.”12 While the large colonies of other ants require intricate nests, and like large human populations are hard to move, army ants avoid investing