The TwdlD¹ mutation has a dramatic effect on body shape, resulting in a squat body shape and reducing the axial ratio (length\width) to just 2.2 (compared to 3.0 in controls). Both the width and length of the pupal case are affected, although the change in length is more readily apparent by inspection.The reduction in axial ratio is similar for both heterozygotes and homozygotes. Adults appear slightly more squat than wild-type. Viability and fertility are unaffected.

TwdlD¹ heterozygous first instar larvae display a cuticle axial ratio of 2.9, whereas wild-type controls exhibit an axial ratio of 3.5.