Drain flies appear in homes, rest rooms of commercial buildings, sewage disposal plants and agricultural facilities that handle moist animal waste. Restaurants, schools and other public buildings may be avoided when drain flies are a nuisance. Bronchial asthma can be caused by inhaling fragments and dust of dead flies. Since these flies originate in filthy conditions, there is the possibility of physical transmission of microbes of human health concern. Drain flies can carry bacteria and other microorganisms from egg-laying sites to food and surfaces that come in contact with food.
Drain fly larvae grow and feed in polluted, shallow water or in highly moist organic solids prevalent in drains. The life cycle of drain flies can be completed in one to three weeks. Adults live about two weeks, with old ones dying and new ones emerging.
The most effective way to prevent drain fly infestations is to eliminate their breeding places. Inside buildings, this would include cleaning the drain pipes, drain traps and other plumbing system components in an attempt to eliminate the bacterial scum (gelatinous rotting, organic matter) that regularly forms on the surfaces of plumbing.
There are no insecticides registered for use in drains or sewage systems, as they can cause major damage of sewer and sanitation systems. In most cases, the larvae seem to be resistant to such treatments.