If you're not bothered by them, they won't harm the dubia but they do breed very quickly. They're a huge pest in Texas during the warm months (10 months out of the year) and I had them in my dubias bin a couple of times. The only way I could find to get rid of it was to take the whole bin outside and shoo away as many flies as I could. I then picked out as many maggots and pupae as I could. I removed the water crystals and switched to feeding as many veggies as the dubia could eat in a couple of hours. About a week of this (shooing and squishing) and the flies were gone. I repeated this process a couple of times during the summer.