The taxonomic history of nominal subspecies of Danaus gilippus is reviewed. The historical record together with analysis of both morphological and molecular characters suggest that the current infraspecific nomenclature is in need of revision. The absence of DNA barcode differences and lack of consistent morphological differences in wing maculation in western and eastern populations in continental North America currently assigned to subspecies D. g. thersippus and D. g. berenice, respectively, raise the possibility that only a single subspecies, D. g. berenice, should be recognized. Recently published isotopic evidence for connectivity between eastern and western populations of D. gilippus, and potential ecological consequences of the relatively low numbers present in the spring and summer breeding range of the eastern migratory populations of the monarch, Danaus plexippus, are briefly discussed.