Spy-fly

From Srafopedia

Spy-flies are beetle-like contraptions from the Afric country in Lyra's world. They are used as, obviously, spies, but are also merciless attackers when sent directly after a person, because due to the nature of it's power, it will never stop until it is destroyed. Inside each one is a set of clockwork, and a spell is used to pin an angry spirit to the spring. They are about as big as a girl's thumb, and dark green in color. In the case a spy-fly is destroyed and the spirit released, the spirit will be angry enough to kill the first person it sees.