The downy emerald (Cordulia aenea) is a species of dragonfly. It is metallic green and bronze in color, and its thorax is coated with fine hairs, hence its name. Like most other emeralds, the downy emerald has bright shiny green eyes. Adults are around 5 cm in length, and are in flight from May through July each year.

This species lives in woodlands near lakes and ponds; like other dragonflies, it lays eggs in water and its larvae are aquatic. It is distributed throughout most of Europe. Although it has been eliminated from some of its historic native area in Great Britain due to habitat loss, dense populations of the downy emerald can still be found there in spots where its ideal habitat remains.

After the downy emerald young emerge from their eggs, they live for three years at various larval and nymphal stages. They are fully grown adults for only two months, during which time they mate and the females deposit their eggs back into the water.

A dragonfly is a type of insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera. It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies are similar to damselflies, but the adults can be differentiated by the fact that the wings of most dragonflies are held away from, and perpendicular to, the body when at rest. Even though dragonflies possess 6 legs like any other insect, they are not capable of walking.

Dragonflies are valuable predators that eat mosquitoes, and other small insects like flies, bees, ants, and butterflies. They are usually found around lakes, ponds, streams and wetlands because their larvae, known as "nymphs", are aquatic.