Glowfly

History
A pretty small insect, the Glow Fly's features are not distinguishable due to the intense luminosity of its light. When it is lit up fully, the bug appears to be much larger than usual.

A Glow fly appears in "The Swamp."

Connection
The lightning bug (or firefly) is likely the closest real life connection to the glowing bug seen in Avatar. Certain species of adult fireflies are able to emit light using an enzyme inside their abdomens.