Dragonflies are insects which are only seen in advertisements for the game, Dragons: Rise of Berk.
Dragonflies are six-legged insects found in the order Odonata. They are known for their two pairs of wings, which enable them to be extremely agile in flight, being able to turn on a dime and move in any direction, even backwards. Dragonflies are similar to damselflies, to which they are closely related, although they differ from damselflies in that they have larger, thicker bodies and that they hold their wings flat and away from their bodies when at rest. Dragonflies start their lives as nymphs underwater, where they hunt small fish, tadpoles, and other water insects. They remain predators as adults, feeding on smaller insects like mosquitos. Dragonflies are living fossils, having been around since the Carboniferous period (around 325 million years ago).
There is no current function for the dragonfly in the DreamWorks Dragons Franchise.
In reality, dragonflies serve as symbols or art fixtures in a variety of different cultures. They also help keep down the populations of various insects, including flies and mosquitos, that can spread disease to humans.