For many years, trap nests have been used to study hole-nesting bees and wasps (aculeate Hymenoptera) and to monitor their diversity and abundance (Krombein 1967; Danks 1971; Godfrey and Hilton 1983; Frankie et al. 1998). Trap nests are valuable for environmental assessment (Tscharntke et al. 1998) and for agriculture through improved pollination by bees (Bosch 1994; Stubbs et al. 1997; Hallett 2001) and biological control by wasps (Harris 1994). Frankie et al. (1988) indicated that shaded environments might be preferred habitats for some solitary bees that use tree holes for nesting. Shading could offer protection from natural enemies as well as wind, rain, and sunlight, resulting in stabilized humidity and temperature. As far as we are aware, ours is the first experimental study to consider the effect of shading of trap nests.