Drain/Moth Flies
Overview
Drain flies, also known as moth flies, sewer flies or filter flies, get these common names because of their appearance and breeding habits. Areas with a continuous build up of microbial bio-films will eventually create a constant layer of undesirable polymer slime, where drain fly larvae thrive and become a nuisance.
Although drain flies are associated with filthy habitats, such as drains, there is little evidence that they can be disease vectors. However, in areas heavily infested with these flies, people could be vulnerable to develop bronchial asthma from breathing in dust and body parts from dead drain flies.
Identification
Adults are small flies about 1/16 to ¼ inch long. They are yellow to brown to black. The key identifying characteristics of the moth fly are the unique pattern of veins as well as their hairy appearance. If crushed they leave a powdery smudge. Wings are held roof-like over their bodies when resting. Larvae are legless and tiny about 1/8 to 3/8 inch long. They have a pale underside with a darker head and tail, and dark bands across their backs. People seldom see the drain fly larvae as they live in protected places.
Biology
They go through a complete metamorphosis, which has four stages, egg, larva (they do not look like adult flies), pupa and adult. Each gravid female lays a mass of about 30 to 100 eggs in moist, decomposing organic materials (for more information about larvae breeding areas, see below under habits and inspection). Eggs hatch in 32 to 48 hours at 70°F. Larvae mature in 9 to 15 days feeding on the decaying organic matter, microorganisms and algae. Pupae occur in or on the surface of the breeding media and, after 20 to 40 hours, new adults emerge. The life cycle can be completed in one to three weeks. Adults live about two weeks feed on flower nectar and polluted water. Wherever warm and wet environments are available, moth flies can be a problem year around with old adults dying and new ones emerging.
Habits
Adult moth flies are often found adhering to the walls of bathrooms, kitchens, or in the basement. They rest during daylight hours on walls near drains, near plumbing fixtures and on the sides of showers and tubs. They are attracted to light and become more active at night and hovering over drains, sinks and other breeding areas. Larvae develop usually in and feed on the gelatinous film (slime) that can build up inside drains, thus the common name of "drain flies". They also can breed in constantly moist organic protected locations with decaying materials, such as under dripping pipes, leaky roofs and refrigeration equipment. Larvae may also breed in large numbers at sewage filter plants.
Management: Inspection & Monitoring
To determine if these insects have been brought in from previously infested materials or they are existed breeding in your location, you need to establish inspection and monitoring program.
Inspection
Look for larva breeding sites in any wet decaying organic matters and moldy areas. In schools, restaurants, food plants, and hospitals most infestations are generated from within the food service areas and custodial closets. In houses, drains and manholes could be the major source of the infestation. Moth flies can also breed in bird feeders, birdbaths, gutters and other similar locations. Leaky pipes and roofs, especially in hard-to-find places can be perfect sites for the larval development, which may go be undetected for a while.
Monitoring
Place insect light traps (ILTs) near places mentioned above and check periodically (moth flies are strongly attracted to light).
Removal of breeding areas
Locate and eliminate larval breeding sites (see above under inspection). Consider using bio-cleaning products to clean inside of the drainpipe and where organic matter may be found. A proven microbial product will eat away grease, food debris and other wastes (larvae food). Foaming bio-cleaning products are preferred forms for this work. They can reach and stick to hard-to-clean surfaces where larvae could be easily missed by using other cleaning forms. Invest enough time to bio-clean all possible larval breeding sources, including drains, under appliances, under floor mats, around plants, dumpsters, cracks and crevices, etc. Never use bleach or any types of boric acid dusts in these areas, as they will deter the bio-product being used in the cleaning. It is suggested to repeating applications at 2 to 4 week intervals depending upon the severity of infestation.
Pesticides
Pesticides can be used to control the adult flies, but this treatment will provide only very temporary benefit unless the source of the larval feeding and breeding is also removed. If pesticide application is needed, your PMP will use a proven aerosol or a space insecticide of pyrethrins or resmethrin to manage adult drain flies, especially in high infestations. Use a proven residual insecticide and apply limited crack, crevice and spot treatments to the following areas:
- Under appliances
- Under floor mats
- Around plants
- Dumpsters
- Cracks and crevices around ceramic tile
- Windows
- Doors
- Grout joints
Repeat applications at 2 to 4 week intervals depending upon the severity of infestation. Apply insect growth regulators (IGR) approved and labeled for drain treatments into and around the downspout and catch basin area, as applicable.
Prevention
Inspect plants carefully before buying for signs of insect infestation. Control moisture problems and any wet environment within a structure. Thoroughly and regularly inspect for sign of infestation. Discard heavily infested materials, as applicable. Remove all old plant material and debris in and around the plant. Regularly practice good sanitation program (remove garbage and any decaying materials inside and outside the structure. Clean the inside of the drainpipes to eliminate the organic matter. Clean dirty garbage containers, wet lint under the washing machine, and even standing water in containers under houseplant pots.
FAQ
Q. I have little flies hanging out around drains in my kitchen and bathroom. It looks like a tiny moth. We keep spraying them, but they keep showing up. What are they? And how to get rid of them?
A. It appears to me that they are drain flies; you can call them moth flies as well. These flies breed in polluted, shallow water or highly moist organic matter. That's why they keep coming back. Long-tem solution to manage drain flies can only be achieved by removing larvae breeding habitats. Remove all moist organic matter, slime, or damp film often accumulating on the sides of drains and overflow pipes, or in sewage disposal beds, septic tanks and moist compost (regularly use bio-cleaning products to clean these places). They have also been found in dirty garbage containers, rain barrels and tree holes.
