A spy-fly was a mechnical insect designed to spy on someone and then return with information. They had clockwork mechanisms worked by evil spirits. The spy-fly would not stop as long as the spirit is inside, and upon release, the spirit would kill the first person it could.
Later, Captain Hartland from the Consistorial Court of Discipline left a spy-fly in the Botanic Garden to spy on Malcolm Polstead's conversation with Lucy Arnold and Charles Capes in the Linnaeus Room however Malcolm managed to capture and kill it before throwing it out of the window.
The CCD managed to breed the flies smaller with even better memories to the point where it could repeat conversations exactly.
- Northern Lights
- The Golden Compass (film)
- The Amber Spyglass (Mentioned only)
- The Secret Commonwealth
- His Dark Materials (TV series), Series 1