Dramatic beetle weapons aren’t just for show

Frantisek Bacovsky

Dramatic beetle weapons aren't just for show

Rhinoceros beetles have an arsenal of weapons at their disposal. Some species sport robust pincers on their heads, while others brandish long, thin spears, and still others wield elaborate pitchforks. A new study reveals that these aren’t just arbitrary adornments: Each species has evolved armaments that perform best at their own style of fighting. To demonstrate this, the authors used an engineering technology called finite element analysis—computer modeling of a structure to calculate the strains and stresses experienced when different forces are applied to it—to simulate the mechanical performance of the weapons of different rhinoceros beetle species under both the species’ own style of battle and other species’ fighting styles. In all species tested, the head horn is inserted under the opponent to pry him from the tree bark on which the beetles live, but the maneuvers are different. The Trypoxylus males (pictured) have long pitchforks that are used to pry and twist opponents off tree branches, whereas the horns of Dynastes function like pliers to lift opponents and toss them to the ground. The horns of Golofa males are long and slender and are used for fencing and pushing opponents off narrow shoots. Depending on the species, the head horns experience vertical bending and twisting (Trypoxylus), vertical bending only (Dynastes), or vertical and lateral bending (Golofa). The horns are strongest and stiffest during species-typical fighting and perform poorly in the context of other species’ fighting styles, the team reports online today in the Proceedings of the National Academy of Sciences. Natural selection for improved performance of dueling males with different fighting strategies likely drove the diversification of weapons in this group of beetles, the researchers conclude.