Drain/ Moth Flies
Nuisance and Biting 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. 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
- 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
- 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
Using a drain cleaner such as Invade Bio Gel Treatment will remove the organic debris and improve santitation.
Invade Bio Foam is another another type of Invade Bio product; particulary useful in commercial establishments. It is a concentrated bio liquid that includes a foaming solution. Invade Bio Foam contains concentrated scum eating and odor eliminating microbes and foaming agents. 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 or other foamers for application. Apply to cracks, crevices and drains where small flies breed. The foam and citrus combination will digest the organic debris present to help eliminate the breeding site.
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 adults do not disappear within a week further treatments and inspection for other breeding sources is needed.
Use Contact Aerosols (Pyrethrins)
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
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.
The top fly light traps recommended to catch drain flies and other smaller flies are the Aura Decorative Fly Light Trap or the Nectar Fly Light Trap. Both of these traps have patented green bulbs with a light spectrum range to attract the smaller flies. These are glueboard traps. Replace the light bulbs once a year.
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
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
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
Bio Treatments For Sanitation
Fly Light Traps