Gee-Jee Fly
From Tardis Wiki, the free Doctor Who reference
The Gee-Jee Fly was a type of small insect that was native to the prison planet known as Varos. (DW: Vengeance on Varos)
While traveling through the infamous Purple zone within the Punishment Dome on Varos, the purple light in the zone altererd the travelers' perceptions, making them believe that the insect inside the room was giant.