Which tools to use? choice optimization in the tool-using ant, Aphaenogaster subterranea

When encountering liquid food sources, ants of the genus Aphaenogaster drop various materials as tools into the food, and then carry the food-soaked tools back to the nest. Although this is one of the most well-documented examples of tool use in insects, we know little about which factors influence their choice of tools during foraging. Here, we investigated the tool-using behavior of Aphaenogaster subterranea by examining, across a range of settings, how tool-using workers deal with various foraging challenges. We used different types of tools and liquid baits with varying distances between the baits and the tools piled around them. Although ants showed the strongest preference for the most easily transportable tools, the frequency of usage of the less preferred larger tools increased when these were the first to be discovered or were more readily accessible to the ants. Additionally, tool selection occurred at two stages: when tools were picked up and dropped into baits, and later, wh...