The expandable network of ant exploration

The Argentine ant, Linepithema humile, adjusts its exploratory behaviour according to group size. Colonies of three different sizes were allowed to explore novel, empty arenas of three different sizes. Ants were tracked on videotape using a computerized image analysis system. At high densities, the shape of searchers’ paths becomes more convoluted; at low densities, paths are more linear. Previous theoretical work shows that this relation between individual path shape and group size maximizes the discovery rate of the group as a whole. Temporal patterns were examined ig density of ants in the novel arena, path shape, and the rate at which area covered by the group expanded. The density of ants in the novel arena increased over the course of 40 min of exploration, but there were no significant temporal patterns of path shape. The area covered by exploring ants increased more rapidly early in the exploration (after 5 min in the novel arena) than later on (after 20 min). The results show that individual ants adjust the shape of their paths in a way that maximizes the discovery rate of the group as a whole. This provides an intriguing new example of how individuals, each acting independently, can generate group-level behaviour.