Drain flies, really moth flies, are eliminated by using an enzyme drain cleaner to remove the organic material the eggs are laid on that bleach, ammonia or bug bombs are not designed to remove.
Moth flies have many names including drain flies and sewage flies. Their fuzzy wings make them look like little moths. Moth flies are a nuisance and are very difficult to eliminate.
Female moth flies most often lay their eggs on the surface of organic buildup in drains and sewers. They may also breed in moist, shady areas outdoors such as under potted plants, or on wet ground areas. The larvae feed on decaying material that collects in drains. They are most active during the evening and seem to be attracted to light.
The larval stage is seldom seen since they live in drain areas or other protected locations. The larvae are skinny and about 1/8 to 3/8-inch long. One way to check a drain as a possible breeding site is to cover the drain with a ‘sticky mouse trap’. Balance the trap on two pencils over the drain and wait a day or two. The little buggers will stick to the trap and indicate where they are breeding.
Most moth flies are harmless to humans, though they may transmit bacteria and other microorganisms from their breeding sites to areas where people are. They do not bite and adult flies only live about two weeks. Most aerosol or spray insecticides will easily kill the adults but not the larvae.
To eliminate the pests, use a bacterial drain cleaner. It will remove the sludge and organic material where the eggs are laid. Bleach or ammonia will not do it.
Enforcer’s Drain Care is one of the enzyme drain cleaners that works. The powered enzyme cleaners are usually stronger than the liquid products. Mix two ounces of powered Drain Care with one quart of warm water and pour in the drain. Try to coat the sides of the drain with the mixture as your pour.
A few treatments of the enzyme drain cleaner should remove the habitat for the eggs and their larvae, thus eliminating the bugs themselves.
Not only will you eliminate the flies, but also you will be cleaning the drains at the same time. Whenever I use enzyme drain cleaner, I pour the whole house starting from the upstairs down and don’t waste any time.