The eastern tiger swallowtail was formerly considered a single species with a vast range into northern Canada and the eastern United States. In 1991, the subspecies Papilio glaucus canadensis was elevated to species level, thus reducing the range of P. glaucus to south of Canada. In 2002, another closely related species, P. appalachiensis, was described by H. Pavulaan and D. M. Wright from the southern Appalachian Mountains. These two species can be separated from P. glaucus by size; P. canadensis is smaller and P. appalachiensis is larger. These two also have a solid yellow bar along the margin of the ventral forewing. P. canadensis females are not dimorphic, and P. appalachiensis females are rarely black.