Traffic rules around the corner: walking of leaf-cutting ants at branching points in trunk trails

Abstract

The existence of transport networks is vital for leaf-cutting ant foraging but may generate overcrowding, reducing the input of food into the nest. We studied how ants turn at branching points, a problematic sector for ant traffic, in leaf-cutting ant species that vary in ant flow and trail design. If the walking of turning ants reduces the chance of collisions, we expected that (a) ants that keep the same lane while turning suffer less collisions than those who change lane, (b) the behavior of keeping the same lane will be higher than expected by chance, and (c) lane fidelity of turning ants should increase as ant flow increases. We recorded the turning movements of 1355 individuals in trail bifurcations from 25 ant nests. Each ant was categorized according to the fidelity to its traffic lane while turning, the number of collisions, and the ant flow at the moment of turning. Ants faithful to their lane had fewer collisions than ants unfaithful to their lane when turning, but only in the two Atta species. Lane fidelity when turning was the most frequent behavior in all species, but this behavior did not increase with increments in ant flow. Leaf-cutting ants appear to follow simple rules to reduce overcrowding: keep walking on the same lane when turning. We discussed the influence of ant flow and trail design on this behavior and the dual role of collisions (information exchange and traffic delay) in trail sectors conflicting for traffic circulation. Bifurcations may be a conflictive sector for smooth traffic in leaf-cutting ants. We showed that ants appear to follow simple rules to reduce overcrowding at theses trail sectors: keep walking on the same traffic lane when turning.