Melanogaster culture problem

Can anybody tell me what the tiny black flys are in the cultures? They are about 1/4 the size of the melanogastor, but fly. They are NOT breding in with the rest of the culture, because my cultured flys continue to stay flightless. I think they originated from a box of crickets, but I can't say for sure. I know they are breeding in one of my vivariums, one of my gecko tanks, my cricket box, and I have found them in my cultures but since moved and quarentined them to eliminate that problem. From what I can tell they have no affect on the animals, or the cultures, but I can't say for sure. Any help is greatly appreciated.

Thanks, Rob Carpenter