Figure out your smell problem and the flies will probably go away on their own. Bad odor can usually be attributed to overcrowding, poor substrate choice, not enough substrate, poor ventilation. I use the huge concrete mixing tubs for mine and only have 3-4 females per tub. I fill them about halfway with bedding and usually don't smell anything other than pine until day 5-6, then I change out everyone on day 7 before it gets smelly.