Behavioral diversity assisting obstacle navigation during group transportation in ant

Abstract Cooperative transportation behavior in ants has attracted attention from a wide range of researchers, from behavioral biologists to roboticists. Ants can accomplish complex tasks as a group whereas individual ants are not intelligent (in the context of thisstudy’s tasks). In this study, group transportation and obstacle navigation in Formica japonica, an ant species exhibiting ‘uncoordinated transportation’ (primitive group transportation), are observed using two differently conditioned colonies. Analysesfocus on the effect of group size on two key quantities: transportation speed and obstacle navigation period. Additionally, this study examines how these relationships differ between colonies. The tendencies in transportation speed differ between colonies whereas the obstacle navigation period is consistently reduced irrespective of the colony. To explain this seemingly inconsistent result in transportation speed, we focus on behavioral diversity in ‘directivity’, defined as the tendency of individual ants totransport a food item toward their own preferential direction. Directivity is not always toward the nest, but rather is distributed around it. The diversity of the first colony is less than that of the second colony. Based on the above results, a mechanical model is constructed. Using the translational and rotational motion equations of a rigid rod, the model mimics a food item being pulled by single or multiple ants. The directions of pulling forces exerted by individual ants are assumed to be distributed around the direction pointing toward the nest. The simulation results suggest that, as diversity in directivity increases, so does the success rate in more complicated obstacle navigation. In contrast, depending on group size, the speed of group transportation increases in the case of lower diversity while it is almost constant in the case of higher diversity. Transportation speed and obstacle navigation success rate are in a trade-off relationship.