Species GS54 infesting SPT 21
Species GS54 was a small, swarming, spaceborne lifeform that fed on electricity. As they were bioluminescent, Starfleet personnel referred to them as "lightning bugs" or simply "bugs".
This species could drain power from spacecraft. Unless removed expeditiously from the ship's exterior, an infestation could disable the ship's systems, leaving its occupants to die of asphyxiation or freezing temperatures.
In 2256, the prison shuttle SPT 21 encountered Species GS54 while passing through an interstellar storm. It took three days for the engineers of the USS Discovery to clear them from the shuttle. (DIS: "Context Is for Kings")