From Guild of Archivists
Found in Eder Kemo

These fireflies can be found floating around in a large swarm near the trooms. Explorers have found them to be useful for lighting up dark areas with their green glow, such as the Eder Gira caves.

The fireflies seem to be attracted to humans, and will eagerly follow whoever will walk through their swarm. However, they will lose trust of the human if he/she runs or jumps, and your collection of fireflies will be halved whenever you do so. They are also afraid of moisture, and will fly away if the human touches rain, steam, and other forms of water. Finally, they will fly away once the human enters the Journey Door. Therefore, one must use extreme caution upon enlisting their help.

Explorers also like to let the fireflies loose in Relto, watching as they swarm around the tiny island. However, they will vanish if the Rain Page is activated.

Their name [cirtE'tam] was given to them by explorer and naturalist Tweek. It is D'ni for "fire organisms".