Myotis midastactus can be distinguished from the species in
syntopy—M. nigricans and M. riparius—by its short, woolly,
and paler fur (LDF: 3.4–5.4 mm; fur is dark and longer in M.
nigricans and M. riparius); plagiopatagium attached at foot,
continuing to the base of the toes as a narrow band of
membrane; and more robust skull, mandibles, and teeth. The
low to moderate sagittal crest is most strongly developed over
the interparietals in M. midastactus, but in M. riparius the crest
is highest in the middle of the braincase; in M. nigricans the
sagittal crest is usually absent or very low.