Euglossa is the largest genus of orchid bees (Hymenoptera: Apidae: Euglossini), with 103 described species from northern Mexico to Paraguay and northern Argentina (Michener 2000; Roubik and Hanson 2004). For many species of these colorful, large-bodied insects females have not been identified. Males generally visit orchids to collect floral oils (see Eltz et al., 1999; Eltz et al., 2003), consequently, considerable information is available concerning male population biology, based on trapping data using artificial baits (reviewed in Roubik and Hanson 2004; Cameron 2004; Roubik 1989). Females do not exhibit such predictable behaviors at artificial baits; they visit a variety of flowers while collecting pollen, nectar, and resins, but they do not visit orchids regularly, and their biology is generally not well known. Most Euglossa species are usually considered to be solitary (Ramirez-Arriaga et al., 1996; Cameron 2004), but the presence of more than one female in the nests of some species indicates some form of sociality (Eberhard 1988; Soucy et al., 2003, Augusto and Garo' falo 2004). The general life cycle and natural history of E. hyacinthina Dressler is described by Eberhard (1988). Information on social behavior and brood sex ratio of this species is given by Soucy et al. (2003), based on nests collected during the late wet season and early dry season (late November to mid-February). The latter study showed that the numerical sex ratio of brood was not significantly different from one:one (female: male), and that numerical sex ratios could be used to infer investment sex ratios because there were no significant differences in body size (as measured by head width) between males and females. This note provides additional details on social biology and sex ratio based on nests of the same species at the same site and time of year. In contrast to Soucy and colleagues (2003), we show that numerical sex ratios are female biased, and that this measure may not accurately reflect investment ratios because females are significantly larger than males using inter-tegular distances, though are not different as measured by head width or wing length.
