Firefly

The Lampyridae are a family of insects in the beetle order Coleoptera with more than 2,000 described species. They are soft-bodied beetles that are commonly called fireflies, glowworms, or lightning bugs for their conspicuous use of bioluminescence during twilight to attract mates or prey. Fireflies produce a "cold light", with no infrared or ultraviolet frequencies.

Biome/Spawn
Fireflies will spawn on any overworld biome, but are kinda rare to find; 10% chance (6-12 insects).

Behavior
They just fly around.

Features
Fireflies are very small and 'glow' in the dark, making them easy to spot specially at night.