Are Drain Flies Harmful? Debunking the Common Myths

Drain flies, also known as moth flies, are tiny, fuzzy insects that are often found around drains, sewers, and other damp environments.

They have strong jaws and feed on the algae, and fungi in the gelatinous film in drains and traps.

Although they may often be seen as a nuisance in households and commercial spaces, the question of their harm to humans and the environment is worth exploring.

Their presence could indicate an issue with drainage or plumbing, such as clogged pipes and leaks.

It is essential to address the issue to prevent potential damage to your property and avoid the growth of mold or mildew.

Are Drain Flies Harmful
A Drain Fly, Source: Sanjay Acharya, Via Wikimedia Commons

Understanding Drain Flies

Appearance and Characteristics

  • Size: Drain flies are small insects, measuring about 1/16 to 1/4 inch long.
  • Body: They have a delicate, fuzzy appearance, with a pale brownish-gray to black color.
  • Wings: Their large wings are held roof-like over their bodies, giving them a moth-like appearance.
  • Antennae: Drain flies possess long, segmented antennae on their heads.
  • Nocturnal: They are most active during the evening and can only fly a few feet at a time.

Life Cycle and Breeding Grounds

Drain flies have a life cycle consisting of four stages: eggs, larvae, pupae, and adults. Their larvae live in the gelatinous film or slime found in drains and traps, feeding on algae, bacteria, and fungi. 

Usually, drain flies complete their life cycle in 3 to 4 weeks. However, the process can accelerate at higher temperatures (85°F, 29.5°C).

Breeding grounds for these insects include:

  • Sewer leaks and back-ups
  • Dirty garbage cans
  • Saucers under potted plants
  • Clogged gutters
  • Moist compost

Habitat and Common Areas

Drain flies commonly accumulate in wastewater systems, such as trickling filters that use biofilm layers for treatment. Over 200 species of worms, protozoa, bacteria, algae, and insects are found in such systems.

They are also found in residential and commercial buildings, mainly in:

  • Bathrooms
  • Basements
  • Kitchens

By understanding the appearance, life cycle, and habitat of drain flies, we can develop effective strategies to manage their populations.

Are Drain Flies Harmful?

Drain Fly Bites

Drain flies are not known for biting humans. These small, fuzzy insects are primarily found near drains and feed on algae, bacteria, and fungi in the gelatinous film or slime in drains and traps.

They do not possess mouthparts for biting, so they pose no direct harm in terms of physical bites to humans.

Potential Health Risks

Although drain flies do not bite, they can potentially pose health risks:

  • Bacteria: Drain flies can spread bacteria by crawling through unsanitary areas like trash and decaying organic matter, then transmitting these bacteria to surfaces they land on.

This indirect contact can contaminate surfaces in homes or businesses.

  • Asthma: If they die near your house, the decaying bodies of drain flies can cause allergic reactions and possibly worsen asthma symptoms for those sensitive to their presence.

Comparison of Drain Flies and Other Common Household Flies

Fly TypeBitingDisease TransmissionAllergic Reactions
Drain FlyNoPossible (indirect)Yes
House FlyNoYes (direct)No
MosquitoYesYes (direct)No

It is worth noting that drain flies are not vectors for diseases like myiasis or microfilaria, which are typically associated with biting flies, such as mosquitoes or horseflies.

However, their presence can be indicative of unsanitary conditions, as they breed in moist areas with a lot of organic remains. Addressing these issues and maintaining cleanliness can help reduce the risk posed by drain flies.

Please keep in mind:

  • Drain flies do not bite
  • They can indirectly spread bacteria
  • They may cause allergic reactions in some individuals

Distinguishing Drain Flies from Other Insects

Fruit Flies

Fruit flies are tiny insects found around overripe and fermenting fruits. They possess a few distinguishing characteristics:

  • Size: around 1/8 inch long
  • Color: reddish-brown or dark brown
  • Attracted to: decaying fruits and vegetables

Drain flies, also known as moth flies, differ from fruit flies in appearance and preferred environments:

  • Size: around 1/16 to 1/4 inch long
  • Color: pale brownish-gray to black
  • Environment: moist areas, typically near drains

Gnats

Gnats resemble fruit flies, but they differ in these aspects:

  • Size: generally smaller than fruit flies (around 1/16 inch long)
  • Environment: damp soil, decaying plants, or water

Sewer gnats, also called sink flies, are another term for drain flies due to their fondness for moist environments like drains.

Fleas

Fleas are wingless parasitic insects that infest animals and humans. Comparing them to drain flies:

CharacteristicsFleasDrain Flies
Size1/16-1/8 inch long1/16-1/4 inch long
ColorDark brown to red-brownPale brownish-gray to black
WingsNoneYes
EnvironmentAnimals, carpets, beddingMoist areas (e.g., drains)

Although fleas and drain flies are different in appearance and habitats, their presence in damp and unsanitary environments can be a problem.

In summary, recognizing the key characteristics of various insects helps distinguish drain flies from others like fruit flies, gnats, and fleas.

Keeping living areas clean and addressing moisture problems will generally help prevent infestations of these pests.

Preventing and Controlling Drain Fly Infestations

Identifying Breeding Sites

Before you tackle a drain fly infestation, it’s essential to identify their breeding sites. Drain flies typically breed in:

  • Polluted, shallow water
  • Highly moist organic solids
  • Muck, slime, or gelatinous film accumulating on the sides of drains
  • Condensate pipes for air conditioners
  • Sewage filtration tanks
  • Septic tanks
  • Dirty garbage containers

Natural and Chemical Remedies

There are various natural and chemical remedies to get rid of drain flies:

Natural Remedies:

  • Vinegar and baking soda: Pouring a mixture of vinegar and baking soda down the drain can help break up the organic material they thrive on.
  • Boiling water: Pouring boiling water down the drain can kill the larvae and remove debris.
  • Apple cider vinegar trap: A mixture of apple cider vinegar, sugar, and soap can be used to trap adult drain flies. Cover the container with plastic wrap and poke holes in it, allowing flies to enter but not exit.

Chemical Remedies:

  • Drain cleaner: Using a drain cleaner can break down the organic matter in the drain.
  • Insect sprays: Applying chemical insect sprays or repellents can help combat adult flies.
MethodProsCons
Natural RemediesNon-toxic, safer for the environment and humansMay require repeated applications
Chemical RemediesUsually faster actingMay contain harsh chemicals, not eco-friendly

Maintaining Clean Drains

Keeping your drains clean can prevent future infestations:

  1. Regularly clean your drains with a mixture of vinegar and baking soda.
  2. Pour boiling water down drains occasionally to remove debris.
  3. Keep plumbing drains and sewage systems well-maintained and free of leaks.
  4. Install drain screens to prevent debris buildup.

By identifying breeding sites, using natural or chemical remedies, and maintaining clean drains, you can effectively prevent and control drain fly infestations.

Dealing with Secondary Issues

Addressing Clogs

Clogs in drains can create a breeding ground for Clogmia albipunctata or drain flies, which belong to the Psychodidae family. One way to deal with this issue is to remove the organic material these flies feed on.

You can use specialized products such as Drano or opt for natural solutions like white vinegar and salt. For example, pouring a mixture of white vinegar and salt down the drain may help break down the organic buildup.

Another option is to use a pipe brush to physically remove the clog. This can be an effective method to dislodge accumulated debris and ensure a smoothly flowing drain.

Pros and Cons of methods:

MethodProsCons
DranoEffective in dissolving clogsChemicals may harm pipes and the environment
Vinegar & SaltNatural and eco-friendlyMay require more elbow grease
Pipe BrushGets rid of physical debrisInvolves manual effort

Eliminating Unwanted Moisture

Standing water, dampness, and lingering moisture create favorable conditions for Psychodidae flies to thrive. Hence, addressing and eliminating unwanted moisture is vital.

  • Regularly check for leaks
  • Ensure proper ventilation
  • Use dehumidifiers in damp areas

By implementing these measures, you can prevent the attraction of drain flies and maintain a healthier, cleaner environment.

When to Call a Pest Control Professional

Drain flies, also known as Psychoda spp., are typically not harmful, but they can be a nuisance when they infest your home. It is essential to call a pest control professional like Orkin in certain situations.

In this section, we will provide examples of some circumstances where it’s necessary to call a professional and briefly discuss the comparison between professional pest control services and DIY methods.

Firstly, if you have a severe drain fly infestation, seeking professional help is recommended. This is because the infestation may spread quickly and become unmanageable with DIY solutions.

Secondly, if you have tried various home remedies and the issue persists, call a pest control professional. They have access to more effective treatments and can identify the root cause of the infestation.

In comparison, professional pest control services typically offer:

  • Expertise in dealing with various pests, including drain flies
  • Access to commercial-grade pesticides and insecticides
  • Comprehensive management plans

On the other hand, DIY methods may:

  • Be less effective and require multiple attempts
  • Lack proper identification and treatment of the infestation source
  • Potentially worsen the situation

However, it’s important to note that seeking professional help might not be necessary for every drain fly issue. If you have a minor infestation, simple home remedies like cleaning the drains might help in controlling the situation.

Moth Fly Larvae

Additional Tips and Techniques

Homemade Traps

One way to address drain flies is to use homemade traps. For instance, a simple vinegar trap can be made using a plastic cup filled with a mix of vinegar and a few drops of dish soap:

  • Pour the mixture into a plastic cup
  • Place the cup near the affected drain

This method will attract the flies to the cup, where they will drown in the solution. Another useful technique is to apply a layer of vegetable oil inside and around the drain, which will trap the flies and prevent them from breeding.

Rain Barrel Protection

Rain barrels can also become breeding areas for drain flies. To protect your rain barrels from becoming infested, you can:

  • Cover the barrels with a fine mesh screen to prevent the flies from entering
  • Regularly remove debris, such as leaves, from the surface of the water to discourage breeding
  • Use a metal pipe brush to clean the interior, particularly if pupal stages are identified
Moth Flies

A quick comparison of these two methods to address drain flies in indoor and outdoor environments:

Homemade TrapsRain Barrel Protection
Effective for indoor environmentsEffective for outdoor environments
Simple and inexpensive to set upRequires some maintenance
Targets adult flies directlyPrevents breeding in water

Remember, drain flies can be identified by their hairy wings and their diet, which consists of algae, bacteria, and fungi.

These insects prefer moist areas and can also be found in compost piles, as they have strong jaws that enable them to break down organic matter.

Keep an eye on these locations, and use the above-mentioned techniques to keep drain fly populations under control.

Conclusion

Drain flies, also known as moth flies, can often be spotted around damp areas like drains and sewers. These bugs do not bite but they can be harmful in many other ways.

They can spread bacteria and trigger allergies. These insects are different from disease-carrying flies and managing them requires cleaning drains, using natural or chemical remedies, and preventing moisture buildup. 

In severe cases, professional pest control may be needed. Stay proactive to reduce their presence and maintain a healthier environment.

Footnotes

  1. Drain Flies – University of Florida 2 3 4 5

  2. Drain Flies – Texas A&M AgriLife Extension Service 2 3

  3. Drain Flies – University of Maryland Extension 2

  4. Flies | UMN Extension 2

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about drain flies. Scroll down to have a look at some of them.

Letter 1 – Bathroom Flies infest Home!!!

The Amazing Replicating Moth?
Location: Washington DC
March 24, 2012 8:45 am
Dear WTB,
So, this particular creature population has been living with us for quite some time- since last summer. At first, they were not much of a problem and we didn’t mind coexisting (especially considering our battle at the time with fungus moths in our plants- ARG!)

Anyway, things have gotten way out of control with these little moth-like bugs. Hundreds populate our homes on a daily basis. Regardless of whether I decide to kill a bunch or not, they do not seem to live very long to begin with but always return in greater numbers.

I am hesitant to call the exterminator because they charge such ridiculous rates just for a basic assessment. In my search on the internet, people insist that they are cupboard moths, but they don’t look like them and do not reside in our cupboards at all.

They can be found all over the windows, walls, and by lights. Our neighbors don’t seem to have them. Do you have any pointers for helping me to understand what they are, how to find the source and take care of them? Thanks.
Signature: Travis

Bathroom Fly

Hi Travis,
The Bathroom Fly is a common household pest that belongs to the family of Moth Flies, hence your confusion as to its identity.  Indoors Bathroom Flies breed in the sludge that accumulates in drains, and that is where the larvae can be found. 

Exterminating the adults will not help with your problem.  You need to get to the larvae.  Pouring chlorine bleach down the drains once a week may help.

Daniel,
You are nothing short of amazing! Thank you so much. I will give your idea a shot and let you know of our progress. 

My only question is whether it is more likely that the moths are coming from a drain outside or are they originating from indoor clogged drains? If outside, I am at a loss. 

However, they seem to be outside the house often enough. More often inside though, I must admit.  Thanks for your thoughts. Bleach in the drains tomorrow and we’ll see.


Thanks, Travis

Chlorine bleach?!
March 27, 2012 7:39 am
Daniel:
Advocating the use of chlorine bleach is to my mind akin to unnecessary Carnage of the environment.  Chlorine is bad stuff.  I wonder if there are less harmful ways to deal with Bathroom Flies. Thanks, Dave Fallow
Signature: Dave Fallow

Thanks, Dave,
Many products that we use on a daily basis, including ones to clean our homes, its furnishings, and even ourselves, are harmful to the environment, and moderation in our habits is about the best that we can hope to do at this point since so much damage has already been done to this fragile planet.

Perhaps a better response would have been that the Bathroom Flies, though a nuisance, are basically harmless.

Letter 2 – Drain Flies bug hydroponic gardener

Subject: What’s this little bug?
Location: 95762 CA, US
January 13, 2014, 11:06 pm
Mid-January in Northern California near Sacramento. These little bugs have been bugging my plants in an aquaponics system in a hoop house. They also seem to leave webs of some kind behind. Any help would be greatly appreciated!

thanks
Signature: Chris Haislet

Drain Fly
Drain Fly

Hi Chris,
This appears to be a Drain Fly or Bathroom Fly in the genus
Clogmia in the Moth Fly family Psychodinae.  We typically get identification requests regarding Drain Flies from homemakers who are perplexed by their appearance in bathrooms and kitchens. 

In the home, the larvae live in the sludge that collects in drains and pipes.  According to BugGuide:  “Larvae feed on algae, fungi and bacteria in sewage and organic sludge; adults feed in polluted water and on flower nectar.” 

We don’t believe they have any interest in your plants, but rather in the hydroponic system itself which may need some cleaning and maintenance.  We are not convinced the webs you mentioned are related to the Drain Flies.  BugGuide also notes: 

“In the home, females lay irregular masses of 30-200 eggs in the organic gelatinous film lining drains, particularly in bathtubs and showers; eggs hatch 32-48 hours after being laid when ambient temperatures are 70ºF (about 20ºC), and larvae pupate 9-15 days later; the pupa stage lasts 20-40 hours; development time from egg to adult is 7-28 days, depending on temperature and food availability; adults live for about two weeks” and “Larvae play an important role in purifying sewage in industrial sewage treatment plants.

Adults are very weak fliers, covering only a few feet at a time in short erratic flights.”

Letter 3 – Moth Fly Larvae

Caterpillar like larvae
March 9, 2010
Recently we submitted a photo that was identified as a moth fly. Thank you for the prompt reply!
The same customer has submitted another photo that looks like some type of larvae. (perhaps the moth fly?)
Cathy’s Crawly Composters
Worm Bin

Moth Fly Larvae

Hi again Cathy,
Based on images we found on the Integrated Pest Management Resources website and on BugGuide, we believe these larvae are immature Moth Flies.

Letter 4 – bathroom flies

I have no idea what has invaded my shower. I am a very clean housekeeper so this little bug has nothing to do with an unclean environment. I live on a lake and maybe that has something to do with it.

Well, here goes the description. It is a very, very small black wormlike bug not even a 1/2″ long and about as big around as mechanical pencil lead. It gets into the edge of the shower and digs into the grout.

I can pour Clorox in the shower and they come out and die. If you do not kill all of them you will see a fat black knit-like fly with big wings a few weeks later. I had the shower taken down and the shower pan liner replaced.

Nothing was in that area. I am constantly pouring Clorox and killing the things but will still see the knit and worm-like bugs. I also have to replace the caulking in the shower frequently because they dig into it and using the Clorox also eats it away.
Do you have any idea what I have and how to get rid of it?

Dear Virginia,
You have bathroom flies, Clogmia albipunctata, which belong to the family of Moth Flies, Psychodidae. You have it exactly right.

The larval form lives in the organic muck which forms inside the drains, and the fact that you live so close to a lake probably compounds your situation since they will also enter the home from the outside where they live in shallow pools and tree holes.

Thoroughly cleaning your plumbing might help, but as long as you continue to kill the individuals you are finding, you will help to control the population.

Letter 5 – Drain Fly

Subject:  Flys
Geographic location of the bug:  Malibu California up in the hills
Date: 07/23/2018
Time: 02:37 PM EDT
Your letter to the bugman:  I keep finding this little fly only in one bathroom of my bathrooms, not any other room. It’s been recently remodeled.
They are not fast and all black
How you want your letter signed:  Debby V.

Drain Fly

Dear Debby,
This is a Drain Fly or Bathroom Fly, a common household nuisance.  The larvae breed in the sludge found in your drains.

Letter 6 – Moth Flies

Big Winged Fly in Worm Bin
March 4, 2010
One of our customers has sent the attached photos of their worm bin.
The conditions in the worm bin are very wet, (muck-like). These tiny, big-winged flies are very numerous covering the surface of the worm bin.

Red wigger worms are numerous also and seem not to be affected by the winged creatures. They look like alien flies. Please let us know what we have here.
Cathy’s Crawly Composters
Worm Bin

Moth Flies

Hi Cathy,
These are Moth Flies in the family in the subfamily Psychodinae.  There is an excellent close up photograph on BugGuide.  Certain species breed in drains indoors, and they are commonly called Bathroom Flies or Drain Flies.

Letter 7 – Suspected Moth Fly Larva from Spain

Subject:  Psychodidae larvae
Geographic location of the bug:  Riudeboix Creek (UTM: 41.81305 2.34131), Collformic, el Brull, Catalonia-Spain
Date: 10/20/2021
Time: 11:42 AM EDT
Your letter to the bugman: 

Hi,
This larvae was sampled in Riudeboix Creek (UTM: 41.81305 2.34131), Collformic, el Brull, Catalonia-Spain on May 9, 2019.
Since then it has been preserved in alcohol 70%.
Can anyone help with the genus ID?
Thank you!
How do you want your letter signed:  iraima

Suspected Psychodidae Larva

Dear Iraima,
The editorial staff at What’s That Bug? does not have the necessary expertise to answer your question, however, we can post your images and enlist our readership to assist. 

We would urge you to post a comment to this posting so people can contact you directly through our comment section.

Suspected Psychodidae Larva (detail)
Suspected Psychodidae Larva (detail)

Authors

  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

10 thoughts on “Are Drain Flies Harmful? Debunking the Common Myths”

  1. I have to disagree that drain flies in a home are only a nuisance. I can’t imagine that the buildup in the drain that these flies develop in can be germ or bacteria free. I am sure these little flies are spreading these germs and bacteria where every they land. There are products that are made specifically to deal with drain fly infestations that won’t harm the environment. They are called Drain Gels. Drain Gels utilize special bacteria cultures and free enzymes to coat drains and cut through the decomposing organic materials that drain flies require to lay their eggs. As an added bonus these “good” bacteria will even help a clogged drain and your septic tank. You can google the term Drain Gel to find the product you need.

    Reply
  2. There are biological products which clean drains by introducing a kind of yeast which eats the sludge out of pipes. It is sometimes a granular product which you mix with warm, not hot, water and pour down the drain at night, then don’t run water into the drain for around 6-8 hours. Using it every week or so, it eats up the sludge and is not a harmful chemical.., is better for the environment and also clears out your drains. One is called Roebic Bacterial Drain Cleaner.

    Reply
  3. This is a little late for this poster, but for those who, like me, have/had this problem in hydroponics, I have a solution: chlorine. This only works for those using synthetic fertilizers, as it will sanitize your system and will interfere with microbial breakdown required to make organic fertilizers function. So, unfortunately it may be illadvised to attempt this an aquatic system. With that said, a chlorine level of 0.5-1.5 ppm will stop them within a system. This works by eliminating the bio-film that tends to build up within most hydroponic setups. The use of chlorine may be continued after the pest is gone, as a preventative measure. It is important not to exceed 1.5 ppm as anything higher than 2ppm may also kill your plants. Also, the initial dosage should be monitored as level will drop as it dose its job. All future doses will be more long lasting. I hope this helps someone.

    Reply
  4. This morning while taking a call i saw and felt something on my ankle that didn’t feel good. A minute later it became quite itchy. It looked like what you have pictured to be a bathroom fly. Thinking about it i do see that in the sink. Your desciption says they dont bite. This one did, no mark though.

    Reply
  5. Dear Debby,
    During my visit to various countries around the globe, I personally found this tinny creature drain flies (Insecta: Diptera: Psychodidae). According to Goodbye Pest basically, it found in a group. Black in clour, breed in dirty stagnant water. not a good flyer, stupidity in nature.

    Reply
  6. Hi!
    Thank you for your reply and time to take a look.
    Maybe there is someone out there that could know? any help more than welcome.
    Thank you for your great work,
    Iraima

    Reply
  7. Hi. I found a natural way to get rid of them. 1 cup of baking soda followed by 1 cup of white vinegar. This will also clean your drain. Try once every 2 weeks or so to begin.

    Reply

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