Animal weapons are massive and their size is integral to fighting success. Males that win fights have disproportional access to females and, as a result, should experience strong directional selection for large weapons. However weapons are often characterized by net stabilizing selection for intermediate size suggesting that there are important and as-yet unstudied costs in these systems. Male frog legged beetles have massive hindleg weapons that they use to gain direct access to females via male-male competition. Males with the largest weapons tend to win the most fights, while males with intermediate weapon sizes have the highest mating success in a population. Here, we characterize how selection is acting on hindleg weapons in the wild and explore potential costs that could be inhibiting strong directional selection for large weapons.