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Male tenebrionid beetles from the Namib Desert are captured by predators more frequently than females. Males exhibit several behaviors that predispose them to an increased risk of mortality from predation. In attempts to find and monopolize females, males are more active on the surface, move more frequently, and travel farther than females. One result of such activity is a bias in captures by predators and pitfall traps. These biased sex ratios differ significantly from those in censused natural populations and an assumed 1:1 sex ratio. We suggest that such differential predation is a major cost of reproduction and can constrain sexual selection.