Dream about killing black flies suggests your irrational thoughts. You are resorting to tricks and superficial means to get ahead, instead of on your merit and accomplishments. You are looking for some reaffirmation, encouragement and approval from others. This points to some negative emotions or anger that is directed at you, but you are oblivious to. You have gone off the deep end in some aspect of your life.
Killing black flies dream states chaos and confusion. You are idling and wasting your life away. You can no longer contain your strong emotions and need to get it out of your system quickly. This is an omen for extreme hostility toward some situation or someone. You no longer have to hide under some disguise or some shield.
If you dreamt about killing black flies:
It may be hard for you to sit still today and not think about work-related issues, even if you are miles away from your workplace. Make a conscious effort to calm yourself down and simply relax. Let go of any nervous, restless energy that you have.