Managing a restaurant means pest control are a big part of my job. You learn early on that one visible bug usually means dozens more that cannot be seen. Our most recent adventure with such an issue began with one or two small flies per day. Within a month, this turned into dozens of small flies per day, and we knew we had a problem. A talk with our commercial floor cleaning vendor determined we had drain flies, and the source would not be easy to get to. Luckily, that vendor was able to supply us with drain treatment that eliminated the problem in a few days.