Structure and composition of trap-jaw ant mandibles

Ant mandibles have evolved to perform a wide variety of functions, including foraging, food processing, defense, brood care and nest excavation. This functional diversity is reflected in the impressive amount of variation in mandible morphology across different lineages of ants. Trap-jaw ants have particularly specialized mandibles: they are capable of rapidly snapping their elongated mandibles shut to catch fast or dangerous prey and experience forces 400 times the ant’s body weight. To test the hypothesis that trap-jaw mandible cuticle is reinforced to resist wear and fracture to a greater extent than mandibles belonging to other ants, we compared the mandible cuticle organization and elemental composition from ant species with dramatically different mandible functions. Four classes of mandibles were investigated: (1) trap-jaw mandibles that experience high impact forces (Odontomachus brunneus), (2) grinding mandibles that experience large forces during plant processing (Pogonomyrmex badius and Atta texana); (3) generalized mandibles that are not specialized (Pseudomyrmex gracilis and Camponotus floridanus); and (4) soft mandibles with relatively thin cuticle (Dorymyrmex bureni and Linepithema humile). We found that the distal mandibular teeth of trap-jaw ants have high amounts of sclerotized exocuticle and are reinforced with the metal zinc. However, they are not reinforced to a greater extent than the other species tested, leaving the specific features of trap-jaw mandibles that prevent their fracturing during a strike still open to question.