• Hamadryas (mythology), the daughter of Oreios and mother of the Hamadryads in Greek mythology

Organisms

• Hamadryas (butterfly), the genus of of brush-footed butterflies commonly known as the Calicoes, Clicks, or Crackers; established by Hübner in 1806 and still valid
• Hamadryas (plant), a plant genus in family Ranunculaceae
  Ranunculaceae
  Ranunculaceae are a family of about 1700 species of flowering plants in about 60 genera, distributed worldwide....
  
  , established by Commerson based on de Jussieu in 1789 and still valid
• Hamadryas, the genus of owl butterflies invalidly established by Mikan in or about 1821; now Caligo
• Hamadryas, a genus of milkweed butterflies invalidly established by Boisduval in 1832; now Tellervo
• Hamadryas, the genus of the King Cobra
  King Cobra
  The king cobra is the world's longest venomous snake, with a length up to 5.6 m . This species, which preys chiefly on other snakes, is found predominantly in forests from India through Southeast Asia to the Philippines and Indonesia...
  
   invalidly established by Cantor in 1838; now Ophiophagus
• Hamadryas, the genus of baboons invalidly established by Lesson in 1840; now Papio
  • The Hamadryas Baboon
    Hamadryas Baboon
    The Hamadryas baboon is a species of baboon from the Old World monkey family. It is the northernmost of all the baboons; being native to the Horn of Africa and the southwestern tip of the Arabian Peninsula. These regions provide habitats with the advantage for this species of fewer natural...
    
    , Papio hamadryas
• Hamadryas, a genus of bulimuline snails invalidly established by Albers in 1850; now Otostomus
• Hamadryas, the genus of the Manchester Moth invalidly established by Clemens in 1864; now Euclemensia