In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Flies
If you dream of flies then you will have many problems and worries. If you swat them away or kill them then you will be freed from the tiring demands of friends.