Parsimonious use of foraging pheromones during nest migration in ants

Decision making is vital to the fitness of all animals, with many social species making consensus decisions that require efficient communication. Chemical signals are the most important tools for many animals, and are used notably by social insects in a wide variety of contexts, from foraging for food to recognition of nestmates. However, chemical cues may be biosynthetically limited and costly to produce, making their use in multiple contexts potentially beneficial. In this study we examined the role of foraging pheromones during nest migrations in the Pharaohʹs ant, Monomorium pharaonis. Using a Y-shaped bridge apparatus, we tested whether ants would prefer migrating to a novel nest site along branches coated with attractive foraging pheromones rather than to a nest site reached via a control branch. We found that ants preferred to migrate to nest sites reached via branches with attractive foraging pheromones, and that there were more queens and workers in those nests at the end of the migration than in nests at the end of control branches. The results show that attractive foraging pheromones are utilized during nest migrations in the Pharaohʹs ant, highlighting the evolutionary pressure to use signals in a parsimonious manner to improve communication during decision making.