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How To Get Rid Of Drain Flies (Sewer Flies)

Drain Fly Identification

Drain flies are small flies, about 3mm. They are usually black, but may be brown. The key identifying trait for this fly is the unique pattern of veins in its wings.*

Drain Flies are also called moth flies, sewer flies or filter flies. Their bodies and wings are covered with numerous hairs. If crushed they leave a powdery smudge. The flies are commonly found around drains, but they should not be confused with the Fruit fly, Phorid fly, or Sphaerocierid fly which also infest drains.

If you see a small fly or gnat type insect flying around in the kitchen, do not assume it is coming from the drains. Check all possible breeding sources (small puddles, grease, rotting organic material, etc.) to help identify the fly.

Understanding the different breeding sources for the flies will help you identify and manage the infestations using pest control.

Breeding Sources of Drain Flies, Fruit Flies, Phorid Flies and Sphaerocerid Flies

  • Drain flies: Drain Flies breed in drains, sewers, septic tanks and soil that has been contaminated with sewage.
  • Fruit flies: Fruit Flies can be spotted around fresh fruits/vegetables, rotting fruits and vegetables, drains, garbage and damp organic materials.
  • Phorid Flies: Phorid Flies are found in sewage contaminated soil, garbage, drains, human cadavers, rotting vegetables and fruit, garbage as well as damp organic materials.
  • Sphaerocerid Flies: These flies may be found in manure, damp organic material, drains, rotting fruits and vegetables and garbage.

Drain Fly Control and Treatment

It is necessary to inspect for breeding sites and remove them. There are many potential areas that serve as breeding sites for the flies. Removing the breeding site is the most important part of a drain fly control program.

Regularly clean any floor drains. Use Invade Bio products to eat the organic matter where the flies breed.

Inspect and Clean – Drain Fly Breeding Sites

  • These flies typically breed in drains, hence the common name of drain flies. This is a good place to begin inspection. They live off debris in the form of a humid film on the drain sides and in the drain trap. If you use something like a knife to scrape the sides, you can examine the sludge for live larvae.
  • Place some tape over the top of drain, with some holes in it for air flow. If the drain flies get stuck on the tape as they exit the drain, you know you have drain flies.
  • Sometimes, drain flies (moth flies) can come from under slab floors from a drain pipe that has broken. They would breed in the organic debis under the slab. Adult flies then enter the living space above the slab through cracks in the slab and back through the drain pipe. To determine if they are coming up through the slab, place the masking tape over the crack as described above.
  • If the suspicion is strong enough that drain flies are breeding under a slab, a hole must be broken through the slab to see if indeed a pipe has broken and flies are breeding there. After a hole is broken through the slab, dig in the soil under the slab and inspect. The organic debris and moist soil may actually be several inches under the surface. The presence of fly larvae and/or adults confirms the site as a breeding source.
  • Sump pump pits and sewers are usually found in a basement area and also prime breeding sites for drain flies (moth flies), particularly in commercial buildings. The sewers and pump pits need to be checked for activity even if it is not close to where the moth flies have been seen flying. Also, inspect the pits of elevators in commercial buildings for excess water or moisture.
  • In homes, drain flies are generally found breeding in bathroom drains, particularly those in showers. Shower pans are prone to leaking and the area under the shower pan becomes a prime moth fly breeding source.
  • Remove all organic debris trapped in small cracks and crevices under the legs and bottom edges of kitchen equipment. The debris needs to removed, thoroughly dried and a long lasting caulk applied to seal the crack.
  • If you strongly believe that the shower is a source, it may be necessary to drill a hole into the area under the shower pan or the wall behind the shower. In most cases where moth flies are breeding in this area, adult flies will begin emerging from the hole within minutes. Drain flies are strongly attracted to light and will fly to the hole drilled through the wall.
  • Inspect crawlspace areas. Sometimes, if the drain pipe is leaking there, a breeding source is found. Look for the presence of adult flies. Spiders may have dead moth flies in their webs.
  • Don’t stop looking when one breeding source has been found. In most cases, several breeding sources will be present.
  • Drain flies, or moth flies, can be found in moist, highly organic debris areas such as sink drains, moist mops, sewage treatment facilities, storm drains, dung and rotten vegetation.
  • Re-grouting tiles to prevent water seepage into walls will stop breeding in those sites. If found in rotting vegetable matter, the source should be destroyed.
  • Clean dirty garbage containers, wet lint under the washing machine, and even standing water in containers under houseplant pots. Outside the home, inspect air conditioners, bird baths, shallow stagnant pools of water and sewage treatment facilities upwind as adult flies will travel with the wind.
  • Drain flies may also breed in moist, shady areas outdoors such as under potted plants, in bird feeders and baths, in moss, in clogged roof gutters, under air conditioners, in thick mulch, or on wet ground areas.
  • In natural settings, moth fly larvae feed on decaying plants and animals. Most moth flies are harmless to humans, though they may transmit bacteria and other microorganisms from their breeding sites to areas where people are. Moth flies do not bite. Adults live about two weeks