A Tolko fly was a species of insect that lived on Cularin.
When the Tarasin constructed a secret cavern in Cloud Mountain to imprison a dangerous creature known as the t'salak, they put tolko flies in it, to serve as an obstacle to prevent the t'salak's release. The flies were placed in a room, where there was a secret button that opened the entrance to the next chamber. A patch of moss that was favored by the flies grew on the button and if there was no light source in the chamber, then the flies would gather on the button to feed, activating it. The Dark Jedi Raik Muun, and later the Heroes of Cularin, both successfully completed the tolko fly obstacle when they tried to find the t'salak.