Megalagrion is a genus of damselflies in the family Coenagrionidae. It contains approximately 26 species, all of which are endemic to Hawaiʻi.
Nymphal Megalagrion live in widely diverse habitats, including the expected streams and pools. Megalagrion also exploit some surprising habitats such as plant leaf axils, waterfall faces, and even damp fern litter far from water sources. M. oahuense is the only species of damselfly whose naiad is terrestrial, living in damp fern litter until metamorphosis.
Many species of Megalagrion are in danger due to habitat loss and predation by non-native fish. To protect them, non-native fish should never be released in Hawaiian streams.