Abstract The size and shape of insect wings vary widely within and among species. One important aspect of this variation is allometry, the relationship between size and shape. Recent predictions suggest that larger insects can fly with a disproportionately smaller wing area or a disproportionately smaller second moment of wing area. These predictions can be used to test whether observed wing allometries represent aerodynamic adaptations. In this study, we quantified wing outline shape and aerodynamic parameters in 139 species of Tachinidae. Consistent with theoretical predictions, the nondimensional radius of the second moment of area increased with thorax width and wing length at a rate lower than expected under isometric scaling. However, we found no evidence that wing area scaled hypoallometrically with thorax width or wing length. Wing shape, described using semilandmarks, was significantly related to wing length. Smaller wings were widest near the center and had more rounded tips, whereas larger wings were widest proximally and tapered asymmetrically toward the tip. These results suggest that wing outline allometry in Tachinidae may be an adaptation to flight aerodynamics.