Danaus erippus is included with other
Nymphalidae, the largest
family of
butterflies with about 6000 species distributed throughout most of the world. It has a reduced pair of forelegs, is brightly coloured, and is included with popular species such as the
emperors, admirals,
tortoiseshells, and
fritillaries. Its wingspan reaches about , with an easily recognizable orange and black pattern. Until 2007, this butterfly was treated as a subspecies of
Danaus plexippus. These species are very similar, but
D. erippus usually has an orange trailing edge of the forewings, while in
D. plexippus it is black. The lineages of the two species are thought to have separated about 2 million years ago. The colour of the wings in males of the southern monarch is paler than in the females. ==Migration==