Random deviations from perfect symmetry in bilateral traits, fluctuating asymmetry, are thought to reflect developmental stability: the ability of an individual to buffer against genetic and (or) environmental stress during development (Palmer and Strobeck 1986). Fluctuating asymmetry is often regarded as an indicator of individual quality or fitness (Møller and Swaddle 1997); however, factors underlying fluctuating asymmetry are not well understood (Markow 1995). It has been suggested that heterozygosity, ploidy, and genomic coadaptation (hybridization) are genetic factors affecting the magnitude of fluctuating asymmetry (Palmer and Strobeck 1986; Markow 1995; Møller and Swaddle 1997). Insects having a haplodiploid sex-determining mechanism present opportunities to examine the relationship between ploidy and fluctuating asymmetry. In hymenopterans, females are diploid and males haploid. Thus the effects of ploidy can be investigated by contrasting males and females within a population (e.g., Clarke 1997). Diploid females, in which deleterious recessives reducing developmental stability could be masked, may be expected to have smaller asymmetry than haploid males (e.g., Brückner 1976; Smith et al. 1997). In this paper, we compare the level of fluctuating asymmetry in forewing venation of males to that of females in the carpenter bee Xylocopa appendiculata circumvolans Smith.