pipe bugs

How To: Get Rid of Drain Flies

Fuzzy winged insects flying out of seemingly clean sinks are the stuff of homeowners’ nightmares. Fortunately, if you can unclog and clean up a drain, you can rid your home of this pesky problem.

Drain flies, also known as moth flies, are a common nuisance in many homes. These pests live and breed inside your plumbing pipes, feeding on decomposing material and laying eggs within the gelatinous slime that collects along the interior walls of your drain. While these insects don’t bite or spread disease, no one likes to see tiny, winged bugs flying out of otherwise clean sinks. If you see some hanging around your kitchen or bathroom, follow these steps to identify the source of drain flies and eliminate them.


  1. Identify affected drains.
  2. Use a pipe snake or pipe brush.
  3. Clear the U-trap.
  4. Pour in enzyme cleaner.

Read on for detailed instructions on how to get rid of drain flies.

STEP 1: Identify affected drains.

Before you can rid your home of drain flies, you need to identify the affected drains. Adult drain flies love to feed and breed in slow-moving or clogged drains, because they provide plenty of decomposing material where the insects can complete their life cycle. If any of your drains are backed up, chances are that those are the root of the problem.

If diagnosing the source turns out not to be that simple, try this other easy trick: Simply cover each drain in your home with a strip of masking tape, sticky side down. (You don’t want to block airflow in your drain, so just make an “X” over each drain opening with the tape.) Drain flies are most active at night, so put the tape on the drains before you go to bed and leave it there overnight to catch any insects that may try to fly out. Check the tape the next morning for signs of bugs to figure out which drains are the source of your flies.

STEP 2: Clean affected drains.

Once you’ve determined which are the problem drains, you need to clean out the slimy gunk that has collected there in order to eliminate the flies’ breeding zones. Resist the urge to pour a bottle of chemical drain cleaner down the drain, as that won’t effectively take care of all the decomposing material in your home’s pipes and traps.

Instead, start by running warm water down the drain. Next, insert a pipe snake or pipe brush down the drain and use a gentle scrubbing motion to remove the built-up slime covering the inside of the drain pipe. A plunger can also be used to help pull out any leftover material from your pipes.

STEP 4: Clear the U-trap.

Open the U-trap under your sink so you can easily reach and remove any other clog-causing remnants that have collected inside.

STEP 5: Use enzyme drain cleaner.

Once you’ve cleared out the gunk, close the system back up and pour an enzyme drain cleaner down the drain to attack any remaining residue that didn’t come off with the pipe snake or brush. This specially designed gel has the additional benefit of coating the inside walls of the pipe to prevent future blockages. Let the gel sit in the drain for several hours, according to the instructions on the label, then run more water down the drain to flush it out.

The length of the life cycle of a drain fly varies depending on the climate and temperature of the drain, but it can last anywhere from eight to 24 days. Once you’ve wiped out their breeding ground, the adults will eventually disappear because there is nowhere left for them to deposit their eggs. After a week, if drain flies are still a problem in your home, it’s safe to assume you didn’t adequately treat all the problem areas. Perform another set of tests (as in Step 1), and look for other spots that need your attention.

Getting rid of winged pests flying around your bathroom or kitchen drain is as easy as clearing the pipes. Read on for the step-by-step.

How To Get Rid Of Drain Flies

Drain Fly Identification

Drain flies are small flies, about 1/8th inch. 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. Using a sanitation drain product like Invade Bio Drain will help destroy the breeding area if they are breeding in the drains.

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

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 – 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 scape 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; 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

Sanitation Treatments – Invade Bio Products

  • Invade Bio Drain Treatment
  • Invade Bio Cleaner
  • Invade Natural Clean
  • Invade Mop Clean
  • Invade Hot Spot
  • Invade Bio Foam

Use Invade Bio Products in the drains. A use of a drain treatment such as Invade Bio Gel Treatment will remove the organic debris, improving santitation.

Invade Hot Spot is a Microbial/Citrus Foam in an easy-to-use 16 oz aerosol. Hot Spot is an aerosol can that contains the same premium microbes and ingredients as InVade Bio Foam. The 360 degree valve allows for foam dispensing in any orientation to easily hit hard-to-reach areas.

If the Phorid flies are breeding in the soil under a concrete slab, the only way to eliminate the infestation is to remove the contaminated soil by breaking through the slab and replacing the soil. Any broken pipes need to repaired. Although this is costly, drilling and treating the infested soil under the slab with residual insecticides does not work.

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.

Invade Bio Foam is another another type of Invade Bio product; particulary useful in commercial establishments. It is a concentrated bio liquid with the use of a foamer. Invade Bio Foam contains concentrated scum eating, odor eliminating microbes and foaming agent. Use this a part of an integrated pest management tool. Use 1 oz per quart, 4 oz per gallon. Apply using a B&G VersaFoamer HH or sprayer to cracks, crevices and drains where small flies breed. The foam and citrus combination will digest the organic debris present as part of pest management. Ultra-concentrated InVade Bio Foam is mixed with water at a rate of 4 oz per gallon (1 oz per quart) and applied using Foam Sprayers.

Invade Bio Cleaner and Invade Mop Clean provide solutions for cleaning organic matter with microbes that greatly improves sanitation.

If adults do not disappear within a week further treatments and inspection for other breeding sources is needed.

Use Contact Aerosols (Pyrethrins)

After breeding sources have been removed a space spray such a pyrethrins, a non residual insecticide can be applied to kill the adult flies. We also carry metered dispensers that use metered aerosols for commercial establishments.

Use Fly Lights

Another tool you can use is insect light traps, however they attract male moth flies with the greatest efficiency. Their use involved with drain flies is limited as a monitoring tool because they can’t eliminate the breeding source.

Biology of Drain Flies

Moth flies (Drain Flies) develop by complete metamorphosis. The entire life cycle ranges from 8 to 24 days.

Moth flies (Drain Flies) lay eggs in a mass of 30 to 100 in a suitable medium. These eggs hatch in less than 48 hours. The eggs form the moth fly( drain fly) are laid in irregular masses in such places as dirty garbage disposal units, water traps in plumbing fixtures, sewage plant filters and almost any where decmposing organic materials are found.

The larvae and pupae of the moth fly live in the thin gelatinous film found in drains, septic tank field lines or filter stones. The larvae feed on sediment, decaying vegetation and microscopic plants and animals. The larval stage lasts from 9 to 15 days before pupating.

The pupal stage lasts from 20 to 40 hours. The newly emerged adult fly is sexually mature on emergence and copulates within the first few hours of its life.

The moth fly (drain fly) is a poor flyer and may be commonly seen ealking or running on walls and other resting surfaces. When they fly in short jerky lines, they fly for only a few feet.

During the day the moth fly (drain fly) adult rests in shaded areas or on walls near plumbing fixtures or on the sides of tubs and showers. Most of the activity of the moth fly (drain fly) occurs during the evening. They may be seen hovering around the sink areas in your home at this time.

*Drain Fly Picture is courtesy of Michigan State Extension

Get Rid of Drain Flies and Moth Flies, How To Inspect and Treat Drain and Moth Flies ]]>