Fig. 1.

Decision algorithm used by each active ant during colony emigration. Search consists of exploratory journeys from the old nest and gives way to assessment once the ant finds a site. Assessment ceases at a rate that depends on site quality, and the next behavior is chosen on the basis of a quorum rule. At low site population, the ant canvasses her fellow active ants by leading them to the site in slow tandem runs (43). Once the population has surpassed a threshold, the ant fully commits to the site and uses speedy transports to bring the passive adults and brood that constitute the majority of the colony.