Neotropical solitary bee-hunting wasps of the genus Trachypus (Hymenoptera: Crabronidae) are ecologically and behaviourally little known. Here, we report information on prey types used by the digger wasp Trachypus denticollis Spinola in central Chile. Female wasps hunted at least 12 species of prey in five families, with Halictidae the most commonly represented. Brood cells are filled with one to eight prey. Cells with greater numbers of prey contained fewer species than expected, suggesting a temporal constancy in individual prey use. A positive linear relationship exists between the number of prey stored in a cell and their total biomass. Larger females tended to collect larger bees than did smaller females; however, because wasp and prey size distributions did not overlap, small wasps may be not constrained to a narrower prey spectrum compared to large ones. We conclude that prey size is an important factor determining prey use in T. denticollis, and these findings match that observed for species of the sister beewolf genus Philanthus and other philanthine wasps.