Adventures Among Ants - Mark W. Moffett [139]
The ants bud new nests when moving not just beyond established borders but anywhere within the colony, and they do it all the time. The frequent shifting of domiciles within a territory is called seminomadism, a practice that seems to go hand in hand with living in temporary encampments. Such camps sound like an army ant bivouac, except, as David explained, instead of staying in one compact nest as army and marauder ants do, “Argentine ants are constantly nomadic, everywhere in a colony at once.”
Supercolony sprawl and suburban sprawl are strongly linked by ants’ and humans’ thirst for water. If I could make the ants glow, irrigated human properties would phosphoresce to their edges, with additional illumination spreading along waterways and in moist natural habitats. These glowing patches would expand and contract as the workers came and went from nests, or created and abandoned nests based on temperature and water availability, a pattern tied to daily and seasonal cycles. But some luminosity would extend into the dark areas, as enclaves of the colony eke out a living up to 200 meters from obvious water sources.17 It’s in such corridors that the invaders do the most harm to California’s scrub ecosystems.
The ants’ constant redistribution of nests minimizes the time spent in foraging and commuting to meals, whatever the food is and no matter if it is clumped or scattered.18 As a result, Argentine ants have no commitment to a particular resource or site but control the useful part of the landscape absolutely. Their trails appear to emerge along lines of frequent passage, much as human paths form on beaten grass, though the ants are guided by scent rather than by the wear of footprints.19 The densest columns develop between nests or from nests to productive food-harvesting sites, with the ants both reestablishing old routes and starting new ones swiftly and easily.
Fanning out from the routes, the workers behave a bit like army ants in acting through sheer force of numbers. Foragers advance over uncharted ground by laying exploratory trails, but they radiate out in a looser, more scattered way than army ants do at their raid fronts.20 Physicist turned biologist Jean-Louis Deneubourg led the team that described this process, in which the whole group generates a trail behind it that leads back to a nest. The success of the operation depends on the workers departing a nest en masse while continually laying pheromones:
The Argentine ants’ exploratory behavior is exceptional in that they mark continually and explore collectively. Whereas other recruitment trails are constructed between two points (e.g., nest and food), their exploratory trails have no known destination, progressively advancing into the unknown. They rapidly lead new explorers to the frontier between the just explored and the about to be explored zones, avoiding situations where ants will end up exploring the same zone twice, and help returning explorers reach the nest directly. A wide corridor of the chemically unmarked area is thus systematically “swept” and marked in a minimum time with maximum economy.21
Each worker can wander at least half a meter from her neighbors, which suggests that, unlike an army ant, she is relatively free to explore on her own. Where their nestmates are scarce, the foragers take straight paths, which spreads them swiftly over new ground. As their numbers increase, the workers begin to take more