The mandibles of neotropical social wasps vary in their shape. Two hypotheses have been proposed as selective forces that explain that variation. The first hypothesis states that the main selective force is the type of material used in the construction of the nest. The second hypothesis states that the main selective force is the type of food. These hypotheses were tested using Independent Contrast analyses and combined tests of significance between nine mandible’s traits, the type of nest material and food source types. Necrophagy and short fiber use are derived conditions in the subfamily and have evolved five times each, while the use of long fibers and live prey are primitive conditions. The mandible structures are related to the nest fiber type but not to necrophagy. Particularly, species that use long fibers have bigger internal dorsal tooth, longer internal ventral tooth, and shorter and more curved mandibles. Similar results were obtained by including plant hairs as a third nest material type.