I remember this story from my school days. A tired fly decides to take rest on the axle of a moving Chariot. While so, he steals a backward glance and finds a lot of dust being generated by the wheels of the Chariot. He says to himself, "I am causing a lot of dust, better move away". So a person who considers himself very important is sometimes referred to as "A fly on the wheel"
A FLY sat on the axle-tree of a chariot, and addressing the Draught-Mule said, "How slow you are! Why do you not go faster? See if I do not ***** your neck with my sting." The Draught-Mule replied, "I do not heed your threats; I only care for him who sits above you, and who quickens my pace with his whip, or holds me back with the reins. Away, therefore, with your insolence, for I know well