The mites tend to be clear and very small.Probaly about the size of a period. (.). They have mite killers that work well.I put my cultures on paper towel that I mist once a week with mite killer and it seems to workout well.I'm not sure how exactly the mites harm the flies but the culture for me stopped reproducing.I suggest having 2 culures to prevent not having flies incase of a die off.Hope this helped.