The function of leaf-caching behavior in leaf-cutter ant ­supply chains

Leaf-cutter ants Atta colombica form supply chains to move leaf fragments from their foraging sites to the nest of the colony. The ants then mulch these leaf fragments into substrate for the fungus they grow for food. The overall efficiency of this transportation system depends on the dynamic integration of the supply rate of the cutter ants, the layout of the trail network and the processing rate of the workers remaining at the nest. In this study, we investigated the contribution of leaf-caches (way stations that can form near the production sites, along the trail, and near the nest) to the foraging efficiency of natural colonies. In this study we tested to see if these leaf-caches were used as buffers to equalize flow rate when leaf delivery and processing rate were mismatched. The nutritional quality of the leaves is important for fungal growth. Therefore, we also tested the cycling of leaves within caches to investigate whether fresh leaves are prioritized and how this occurs. Results from this study have important implications for our understanding of the caching behavior of leaf-cutting ants and the optimization of self-organizing supply chains.