Fragment-size determination and size-matching in the grass-cutting ant Atta vollenweideri depend on the distance from the nest

Abstract

Fragment-size determination by workers of the grass-cutting ant Atta vollenweideri and the extent of size-matching between ant size and fragment size were investigated as a function of the distance from the nest. Foragers and their loads were sampled in four different sectors along a 30-m foraging trail in the field: directly on the harvested source, in the patch, on the trail and close to the nest. Ants sampled on the source immediately after cutting were significantly larger than carrying ants on any trail sector, whereas body mass did not differ among other samples. Thus, foraging was partitioned into at least two stages, with large ants cutting the source and smaller ants carrying the fragments to the nest. Fragments collected directly after cutting were significantly larger than those carried on the trail, indicating that the fragments were cut once again on their way to the nest. Size-matching depended on the trail sector considered. It was stronger in ants sampled closer to the nest, suggesting that carriers either collect dropped fragments according to their body mass, or cut fragments out of the dropped fragments in sizes corresponding to their body mass prior to transport.