Native bees provide important economic and ecological functions that include pollination of agricultural crops and natural plant communities, thus conservation of their declining populations is important. The use of pan traps for collecting and monitoring bee populations has become widespread because the method samples widely different habitats with equal effort. However, to the best of our knowledge no efforts have attempted to quantify their efficiency. We measured the efficiency of pan traps at collecting bees by using video cameras to record individuals coming to the traps. Videoed bees were classified as approaching the trap, making contact with the trap, or being captured. During 52 h of video, 16 bees (19%) were captured, 25 bees (30%) made contact with the trap but were not captured, and 42 bees (51%) approached the trap and departed without making contact. The results of this study suggest that pan traps collect <20% of the bees that are attracted to it and are likely to overestimate the abundance of smaller-bodied bees such as Lasioglossum spp.