Actually, yes they do harm the flies to a significant degree. Some mites are parasitic on the larvae. Even the detritus mites cause a problem as with each succesive culture made from the last, the mites get worse and worse and your culture produces way less fruit flies.I'm a bug guy, not a frog guy, so I'm curious why everybody considers the mites so dangerous? They don't harm the flies to any significant degree, unsightly as they are! Do mites harm frogs or infest vivariums by vector of fruit fly cultures?