Tribolium castaneum (Herbst) is a cosmopolitan pest of stored products, grain processing, and food warehouses. This study was initiated to more fully characterize the role of structure, sanitation, and trap location on capture of T. castaneum in pheromone-baited pitfall traps commonly used in insect monitoring programs. Food patches, spatial structure, and trap position were manipulated in pilot scale warehouses with a known density of insects. Significantly greater quantities of insects were captured in traps placed in warehouses without food patches than those with food patches. Insects tended to be captured with greater frequency in the corners and underneath shelves than in the middle of warehouses. Correlation between actual density and trap captures was stronger in warehouses without food patches, suggesting that sanitation is an important part of pest monitoring. Finally, placement of concrete blocks in the middle of the warehouse did not increase the number of beetles captured in that area compared with warehouses without concrete blocks. Results from this study should be considered when developing guidelines for trap interpretation.