Eresia nauplius, the Peruvian Crescent or Nauplius Crescent, is a butterfly of the Nymphalidae family. It was described by Hewitson in 1852. It is found in most of the Amazon region. The habitat consists of forest edges with low vegetation, including river banks, forest clearings, glades and roadsides. The wingspan is about 45 mm. Adults feed on flower nectar and males have been observed imbibing moisture from sandbanks, river beds, drying pools or peccary wallows.