Animal weapons commonly must resist large loads and impacts generated by pushing, striking, and even twisting. The performance of weapons can be central to male reproductive success; yet, not all weapons can weather the battle. Few studies have investigated the influence of nutrition the stability of the weapon structure. We focused on the effects of adult nutrition on the insect weapon, something previously not examined in any of the millions of species of insects and other arthropods. The lack of studies in this area may seem obvious; when an insect molts into adulthood, its weapon skeleton hardens and retains the same external size and shape for life. However, this static exterior may hide significant changes on the inside. In this study, we focused on the effects of early adult nutrition on weapon integrity using the leaf-footed cactus bug, Narnia femorata (Hemiptera: Coreidae). Males of N. femorata use their enlarged and spiny hind limbs to strike and squeeze other males in competition over reproductive opportunities. We found that just three weeks of high-quality adult nutrition resulted in 82% greater puncture resistance of the hind leg weapon than the weapon of those with poor-quality nutrition. The higher puncture resistance was correlated with a significant increase in skeletal (cuticle) mass; high-quality nutrition led to a 125% greater cuticle mass of the hind leg. Our results demonstrate that adult nutrition may be a vital unexplored factor influencing weapon performance during battle. Our findings also highlight that external size may be deceiving and may not always serve as an honest signal of performance.