Spy Flies are small, fast artificial creatures that are spies to the Magisterium. These things are driven by bad spirits and have poisonous stingers. If a person is stung by a spy fly, the person falls asleep. Spy Flies were seen in The Golden Compass, where two of them were sent by Marisa Coulter to get the alethiometer. One got away and one was captured when Farder Coram trapped it. Lyra later released this one to sting Mrs. Coulter.