As indicated in their name, leaf-cutter ants cut tree leaves and bring the pieces to their nest where they are used as substrate to grow mushrooms. Usually, when the path toward the nest is clean, these pieces of leaf are large. But when the path is obstructed by twigs for instance under which ants have to pass, are they still able to supply their nest with a sufficient amount of leaves? This question was investigated by Audrey Dussutour and her collaborators in a recent article published in Animal Cognition. Hereafter is the abstract of this article that summaries their results better than I could do.

“In this paper we investigate the flexibility of foraging behavior in the leaf-cutting ant Atta colombica, both at the individual and collective levels, following a change in the physical properties of their environment. We studied in laboratory conditions the changes occurring in foraging behavior when a height constraint was placed 1 cm above part of the trail linking the nest to the foraging area. We found that the size and shape of the fragments of foraging material brought back to the nest were significantly modified when the constraint was placed on the trail: independent of their size, forager ants cut smaller and rounder fragments in the presence of a height constraint than in its absence. This size adjustment does not require any direct sensory feedback because it occurred when the ants cut fragments in the foraging area; no further cutting was done when they encountered the constraint. This points to the existence of a template that ants store and use as a reference to adjust their reach while cutting. Remarkably, despite the decrease in the foraging material brought to the nest per capita the colony was still able to improve its foraging performance by doubling the number of transporters. This study illustrates the flexibility of foraging behavior exhibited by an ant colony. It provides a rare example of insects finding an intelligent solution to a problem occurring in a foraging context, at both the individual and collective levels.”

And to illustrate these findings, hereafter is a short video that was published by the New Scientist: