Qualitative taxonomic characters based on differences in linear eye measurements were converted to qualitative scores for Efferia group species, and statistical analyses of intraspecific and interspecific variation were perfomed. Sexual dimorphism noted for E. albibarbis is the first documented for an eye morphology character in Asilidae, and may be analogous to sexual dimorphism described in a holoptic-dichoptic context for other species of Diptera. Interspecific variation in E. albibarbis Macquart and E. aestuans (Linnaeus) demonstrates that robust comparisons among species cannot rely on single exemplars, and differences among specimens based on sex and geography should be considered during subsequent eye morphology studies in Asilidae. The variables identified in this study demonstrate that a wide variation in eye morphology exists among Efferia group species that can be examined in a quantitative context. Detailed accounts of intraspecific variation are considered crucial for comparisons among species of Asilidae, and interspecific comparisons of eye morphology are likely to demonstrate biologically significant results in studies of monophyletic taxa and ecological guilds.