A Rassilonian Timefly, or Temporanius clepcydras, was a time-sensitive insect. They communicated by exchanging vortex pheromones. Their shells were carcinogenic and artronic and could cause chronal tumours. They were hunted mercilessly, so much that when the Eleventh Doctor discovered a pair, he believed them to be the last in existence. Shortly after, the planet on which they resided was wiped out by a Suicide Specialist Sontaran's eschatomic warhead. Abslom Daak saved the Timeflies, setting them free outside the Stormcage Containment Facility. (COMIC: The Judas Goatee) Alice Obiefune took the TARDIS back to Stormcage where she used the Timeflies to activate the chronal tumour in the Master's TARDIS. (COMIC: Running to Stay Still)
The Tenth Doctor saw some timeflies when he visited ancient Gallifrey. (COMIC: Old Girl)