Firefly (Franchise)

Fireflies are insects that appear minimally in How to Train Your Dragon Franchise.

Description
Fireflies (or "lightning bugs") are a family of beetles of the order Coleoptera known for their ability to produce light. Through the use of specialized organs in their abdomens, they’re able to set off chemical reactions that result in a blinking or glowing light. This process is commonly known as bioluminescence. Some fireflies blink their lights on and off in fancy patterns, others just emit a steady glow, and some can’t do either of those things. In fact, despite their common name, many firefly species are unable to produce any light at all.

The life cycle of a firefly is called metamorphosis. They start out as eggs in the ground and then quickly grow into larvae (sometimes called glowworms), which can spend up to several years underground. In the spring, the larvae turn into pupae and, subsequently, adult beetles.

Function
Fireflies do not have a function in the franchise, nor in real life.

Dragons: Rise of Berk
During the Eternal Night updates (which are around Halloween), fireflies can be seen flying around Berk.