The Downy Emerald (Cordulia aenea) is a dragonfly within the family of Emerald Dragonflies (Corduliidae).
The Downy Emerald (47-55 mm) is the only species of its genus in Europe.
Like most other emeralds, the Downy Emerald has bright shiny green eyes.
In Europe, it can easily be confused with the Brilliant Emerald (Somatochlora metallica) and, in eastern Europe (like Hungary), with the Balkan Emerald (Somatochlora meridionalis), which usually have a more obvious metallic green body and have yellow markings on the face.
Until 2006, Somatochlora meridionalis was considered as the East-Mediterranean subspecies of Somatochlora metallica but is now treated as a full species.
In addition, the male Downy Emerald has a more strongly club-shaped tail than the male Brilliant Emerald.
The female Downy Emerald (on the photo) can be distinguished from the female Brilliant Emerald by having a much smaller ovipositor (near segment 8).
The ovipositor of the female of the Brilliant Emerald is rather large and sticks out in a 90 degree angle.

Hortobágy-Halastó, Hortobágy National Park, Hungary, 2 May 2019