Abstract Sexually selected traits are often assumed to convey information to conspecifics about the condition and genetic quality of an individual. However, sexually selected traits also are hypothesized to be among the most rapidly evolving and phenotypically plastic traits in natural populations. When found, such variability can bring into question the reliability of these traits as sexually-selected signals. Here, we examine the expression of a male weapon over multiple spatial and temporal scales in the wild. Specifically, we measured the expression of enlarged hind femora across and within populations of the Neotropical bug Leptoscelis tricolor Westwood (Hemiptera: Coreidae). We found significant variation in the size of this trait across populations and even within a population according to the plant species where adult males were collected. We also found differences in the intercept of the scaling relationship with body size; for a given body size, males in some populations express larger sexually selected traits than males in other populations. These results support the hypothesis that the expression of sexually selected traits is dynamic over space and perhaps time. Such patterns suggest that environmental variation or small amounts of movement across genetically differentiated populations may confound the reliability of information contained in the expression of these traits.