Firefly

Fireflies are flying insects that live in the Northern Air Temple. It is unknown if they also inhabit other Air Nomad Temples or nation. These creatures are used as non-flammable light source. They were seen when the Mechanist led Sokka to the gas room through a dark corridor in the temple.

Anatomy
Fireflies are characterized by a pair of slender, jointed antennas, forewings or elytron and a narrow prothorax. They have a mechanism of bioluminescence that likely works by emitting a light from the abdomen. The color of this light is similar to a light green or light blue.

Connection
The fireflies seen in the temple has mostly a resemblance to the subfamily of Lampyrinae, luminescent nocturnal fireflies.

The ancient Chinese sometimes captured fireflies with the purpose of lighting. It was also a widespread practice in ancient India. But since these were short term solutions, the use of other objects was more prevalent.

Place in the World of Avatar
A group of these insects are captured in a transparent container and used them as lanterns. The Mechanist is maybe the creator of this device due to he had to use a non-flammable light source because he used the lantern in a dark stone staircase leading to a gas room with leaks.

Trivia

 * In addition the hermit crab, the fireflies are probably other creature that have survived to the genocide and have remained in the temple since then.