Social learning through improved tool use efficiency in red fire ants

Various tool use behaviors are prevalent among a diverse species of ants. Despite tool use being a subject of increasing interest in social insects, whether insects can learn to improve these behaviors has not been studied. Recent work has illustrated that red imported fire ants, Solenopsis invicta, will pave a path by covering toxic or sticky surfaces with available particles to facilitate foraging. The present research investigated if red fire ants can display social learning by collectively learning to improve the efficiency of path construction. In our novel experiments, we coated a petri dish with vaseline, which is aversive to fire ants, added glitter by the dish, and placed food at its center. We then presented this setup to a food-deprived colony fragment composed of approximately 2,500 worker ants. Ants used glitter to cover the vaseline and create a path across the dish, initiating from the periphery and gradually reaching the food at the center. Our findings revealed that red fire ants can improve route efficiency over repeated trials by paving less area in a narrower route in order to reach the food source. Not only did the paths become increasingly narrow and coherent throughout trials, but each ant also became responsible for a greater share of the coherence. Our results show, for the first time, collective learning—when animal groups improve their performance collectively over time—with respect to tool use behavior in social insects.