Fly
In agrarian society, flies (like rats) were associated with the devil. They are drawn to death and decay; the devil figure Beelzebub means "lord of the flies," and so on.
Flies that constantly buzz around aimlessly can express endless, meaningless activities. They fly about, annoy, suck blood, risk infecting others, and as such, are sometimes a symbol of autonomous complexes. (von Franz 2002, p. 29.)