Large ants do not carry their fair share: maximal load-carrying performance of leaf-cutter ants (Atta cephalotes).

Although ants are lauded for their strength, little is known about the limits of their load-carrying abilities. We determined the maximal load-carrying capacity of leaf-cutter ants by incrementally adding mass to the leaves they carried. Maximal load-carrying ability scaled isometrically with body size, indicating that larger ants had the capacity to lift the same proportion of their body mass as smaller ants (8.78 times body mass). However, larger ants were captured carrying leaf fragments that represented a lower proportion of their body mass compared with their smaller counterparts. Therefore, when selecting leaves, larger ants retained a higher proportion of their load-carrying capacity in reserve. This suggests that either larger ants require greater power reserves to overcome challenges they encounter along the trail or leaf-cutter ants do not select loads that maximize the overall leaf transport rate of the colony.