There are four or five species of flies that can be found breeding indoors. If fly problems are seasonal or re-occurring the source may be outside. Proper identification will help lead to the breeding source and the type of sanitation needed to control the fly problem. Flies can breed quickly and go through a generation in 10-14 days. Fruit flies breed in yeast associated with moist, fermenting organic material in trash cans, recycling bins, compost and sour mops.
Drain flies breed in floor drains, sink overflows, and unused urinals, sump pumps and sewers.
Filth flies such as houseflies and blowflies breed in garbage and animal waste. They do have a public health concern as they are capable of mechanically transmitting a number of diseases. Fungus gnats breed in potting soil of indoor plants and in moist organic matter. Cluster flies seek shelter in buildings during the fall. Indoors electric fly traps can be used in food or storage areas.