Why Do Drain Flies Keep Coming Back? A Friendly Guide to Preventing Their Reappearance

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Drain flies can be a persistent nuisance in your home, despite your best efforts to get rid of them. One of the main reasons these small, fuzzy insects keep coming back is because they thrive in moist environments, often laying their eggs in the slimy buildup of drains and pipes.

In order to understand why drain flies return, it’s important to know their breeding habits. They lay their eggs in the gelatinous film found in drains and traps, which contains organic matter, bacteria, and fungi that the larvae feed on. This makes areas like your bathroom and kitchen sinks, shower drains, and even dirty garbage cans perfect breeding grounds for these pests.

To prevent recurring infestations, it’s crucial to address the root cause of the problem. By keeping your drains clean and regularly removing any organic buildup, you can create an inhospitable environment for drain flies to lay their eggs, thus reducing the chances of them coming back. Maintaining cleanliness and proper sanitation in your home will go a long way in stopping these pests from returning.

Understanding Drain Flies

Drain flies, also known as moth flies or filter flies, are small, gray insects that breed in polluted, shallow water or highly moist organic solids. You might find them around drains, sewage filtration tanks, septic tanks, and damp compost. These breeding sites provide ideal conditions for drain fly larvae to grow into adult drain flies.

Characteristics of drain flies include:

  • Small size (about 1/8 inch long)
  • Gray or dark color with fuzzy appearance
  • Wings covered in fine hairs

Drain flies are not dangerous to humans, but they can be a nuisance. They thrive in moist environments, so the key to preventing their re-infestation is to eliminate their breeding grounds. Regularly cleaning drains and keeping areas around sinks and pipes dry can help keep these pests at bay.

In comparison, here’s a brief overview of drain flies and another common household insect, fruit flies:

Insect Appearance Breeding Site Prevention Method
Drain Fly Small, gray, fuzzy Drains, sewage tanks, moist compost Regular drain cleaning, reducing moisture
Fruit Fly Tiny, red eyes, tan or brownish Fruits, vegetables, drains Store fruits in closed containers, clean drains

Remember, if you find drain flies in your home, it’s essential to identify and address the source of the infestation, such as a clogged drain or damp environment. Following these prevention tips and maintaining a clean, dry living space will help minimize the chances of drain flies recurring in your home.

Where Drain Flies Breed

Inside the Home

Drain flies can find breeding sites in various locations inside your home. They are particularly attracted to moist environments with organic materials. In the bathroom, you might find them breeding in drains, including the sink, shower, and even the floor drain. These flies can also be a common problem in kitchens, breeding in sink drains and dirty garbage containers.

For example, a clogged kitchen drain with leftover food scraps can be an ideal breeding ground for drain flies. Keep an eye out for these pests around areas with standing water or excess moisture.

Outside the Home

Outside your home, drain flies may find suitable breeding sites in multiple locations that provide moisture and organic materials. They might breed in sump pumps or basement floor drains where water accumulates, leading to moisture and possible organic buildup.

In addition, drain flies can breed in:

  • Septic tanks
  • Compost piles
  • Moist areas near exterior walls
  • Rain barrels or puddles of standing water

You might also spot drain flies around your home’s exterior walls and windows, as they are attracted to light. Ensure that you keep these areas clean and properly maintained to avoid creating breeding grounds for drain flies.

Life Cycle of Drain Flies

Egg Stage

Drain flies lay their eggs in polluted, shallow water or highly moist organic solids, like the muck and slime accumulating on the sides of drains and condensate pipes1. Sewer leaks, dirty garbage containers, and rain barrels can also be breeding grounds for these insects. In similar environments, you might find gnats laying their eggs, too.

Larval Stage

Once the eggs hatch, the larvae feed on bacteria, fungi, and algae in the surrounding slime2. They are difficult to drown, as they can trap air bubbles and remain submerged for a day or more3. These maggots go through several stages of development before reaching the pupal stage.

Pupae Stage

Following the larval stage, drain fly larvae transform into pupae. This is a transitional stage between larvae and adults. The drain fly life cycle takes about 10 to 15 days at approximately 70° F4. In this stage, the pupae undergo a complete metamorphosis to emerge as adult drain flies.

Adult Stage

Adult drain flies are tiny (1/5 to 1/6 inch long), fuzzy, and dark or grayish5. They are weak fliers, flying only a few feet at a time, and are most active during the evening6. It’s important to eliminate them and their breeding grounds to avoid infestations in your living environment.

Remember, managing the population of drain flies depends on your ability to remove their breeding sites and prevent them from laying eggs. Keep your living areas clean and dry, especially near drains and organic waste, to deter these pests.

Why Drain Flies Come Back

Insufficient Cleaning

One major reason drain flies keep coming back is because of insufficient cleaning. These pests feed on the organic material found in the slime layer that accumulates in drains, pipes, and traps. If you only clean the surface of your drains, you are not eliminating their food source.

  • Use a stiff brush for deeper cleaning
  • Flush drains with boiling water

Continuous Breeding Grounds

Drain flies can breed rapidly, and if you don’t address their breeding sites, they will continue to return. They can lay eggs in moist areas like sewer leaks, dirty garbage cans, or the slime in drains and traps. Make sure to identify and eliminate such areas.

  • Regularly check for plumbing leaks
  • Keep garbage cans clean and dry

Seasonal Factors

While drain flies can be a nuisance year-round, they are more prevalent during specific seasons or environmental conditions. Higher humidity can increase their numbers, as it promotes the growth of organic material they feed on. Therefore, controlling humidity levels can help deter drain flies.

  • Use a dehumidifier
  • Improve ventilation

Ineffective Pest Control

If you’re using pest control methods that don’t specifically target drain flies, they may not be effective in managing the infestation. It’s important to use a strategy that targets both adult flies and their larvae.

  • Employ mechanical cleaning
  • Use targeted chemical treatments

Preventing Drain Flies Return

Hygiene and Cleaning

To prevent drain flies from coming back, it’s crucial to maintain proper hygiene and cleanliness in your home. For instance, clean your kitchen daily, as drains and garbage areas are common breeding grounds for these pests.

  • Regularly clean sink and drain areas with a mixture of baking soda and vinegar, which helps remove organic material that attracts drain flies.
  • Move garbage containers away from your house to prevent attracting fruit flies and other pests.
  • Dispose of rotting fruits and vegetables as they attract fruit flies.

Water Control

Stagnant water attracts drain flies, so controlling the water sources in your home is essential for prevention.

  • Fix any leaking pipes to avoid water buildup.
  • Regularly empty and clean items that collect water, like plant saucers or pet water dishes.

Pest Control Methods

Use a combination of pest control methods to deter drain flies efficiently.

  • Use chemical treatments, like Drano, to clean clogged drains that may harbor drain flies. Be sure to follow the product’s instructions carefully to prevent any damage to your plumbing system.
  • Place traps with fruit fly attractants near potential breeding areas to catch and monitor the flies.
  • Consider repellents or natural solutions, such as essential oils, to deter drain flies from settling in your home.

If you’re unsuccessful in controlling the drain fly population on your own, seek professional help from pest control specialists. They have the necessary tools and expertise to get rid of drain flies and provide useful advice for long-term prevention.

Natural Ways to Get Rid of Drain Flies

Homemade Traps

One easy and cost-effective method to eliminate drain flies is by creating homemade traps. Many everyday household items can be used for this purpose:

  • Apple cider vinegar trap: Mix equal parts apple cider vinegar and water, then add a drop of dish soap. Pour the mixture into a container and cover it with plastic wrap. Poke small holes in the plastic wrap for flies to enter but not escape. The vinegar will attract the flies, while the soap breaks the surface tension, causing them to sink and drown.

  • Sugar and duct tape: Mix sugar with a little water and spread it onto a strip of duct tape. Hang the sticky trap near the drain where the flies are most active. They’ll be attracted to the sugar and get stuck on the tape.

Natural Repellents

Using natural remedies to repel drain flies can help prevent their return:

  • Baking soda and vinegar: Mix equal parts of baking soda and white vinegar, then pour it down the drain. This combo will create a foaming action that effectively cleans the drain, removing organic matter that drain flies feed on.

  • Boiling water: Pouring boiling water down drains helps remove built-up residues that attract drain flies. Regularly flushing drains with hot water is an easy way to keep these pests at bay.

Biological Pest Control

  • Green Gobbler enzyme cleaner: This environmentally-friendly product breaks down organic matter in pipes, which helps eliminate drain fly breeding grounds. Simply follow the instructions on the label for application.

  • Microbes: Introducing beneficial bacteria and microbes into your drains could help reduce drain fly populations by breaking down their food sources. Certain products available on the market claim to provide this benefit, but results may vary.

In conclusion, drain flies can be a nuisance, but using homemade traps, employing natural repellents, and introducing biological pest control methods provide effective and low-cost ways to eliminate these pests and keep them from coming back.

Chemical and Professional Methods

When dealing with drain flies, you might find that chemical and professional methods are necessary to fully tackle the issue. Here are a few approaches you can consider.

Drain Cleaners and Drano: For a quick fix, you might try using store-bought products like chemical drain cleaners or Drano. These can help clear your drains and reduce the chances of prolonged infestation. However, keep in mind that chemical sprays and traditional drain cleaners can be harmful to your pipes if used improperly.

Pest Control Professionals: If you find yourself constantly battling drain flies, it might be time to enlist the help of a pest control professional. They can identify the root of the problem and apply specialized treatments like insect growth regulators.

Enzyme Cleaners: An alternative to harsh chemical drain cleaners are enzyme cleaners. These products use natural enzymes to break down the organic matter that attracts drain flies, like roaches. Not only are they generally safer for your pipes, but they also help eliminate the breeding grounds for pests.

Here’s a comparison table:

Method Pros Cons
Chemical Drain Cleaners Quick and easy solution Can damage pipes if used improperly
Pest Control Professionals Can identify and treat the root of the problem Costly and may require multiple visits
Enzyme Cleaners Safe for pipes, targets breeding grounds May take longer to see results

In conclusion:

  • Use chemical drain cleaners and Drano with caution to avoid damaging your pipes.
  • Consult a pest control professional for expert assistance.
  • Give enzyme cleaners a try for a more eco-friendly solution.

Remember, finding the right method for your situation is essential in keeping drain flies from coming back. Don’t hesitate to explore all your options and seek professional advice where necessary.


Drain flies can be a persistent issue in homes and commercial buildings, often reappearing despite several attempts to eradicate them. The main reason for their recurrence is their breeding ground in the gelatinous film or slime found in drains and traps, which provides them with an ample food source of algae, bacteria, and fungi1.

To address a drain fly infestation effectively, one should start by identifying the source of the problem. Focus on areas that accumulate moisture, such as shower drains, sink traps, and even saucers under potted plants4. A thorough cleaning of these areas using a suitable cleaning solution can help eliminate the breeding grounds for these pests.

However, merely using cleaning solutions may not guarantee a drain fly-free home. In some cases, homeowners who return from vacation might be met with an unexpected infestation5. This could be caused by factors like sewer leaks, back-ups, or clogged pipes4.

In conclusion, addressing a drain fly infestation effectively involves consistent maintenance and vigilance in keeping drains clean and free of potential breeding grounds. Establishing a regular cleaning routine and promptly dealing with any plumbing issues are essential steps in preventing the recurring nuisance of drain flies.


  1. NC State Extension Publications 2

  2. University of Maryland Extension

  3. Entomology – University of Kentucky

  4. Entomology – University of Kentucky 2 3

  5. Ohioline – Ohio State University 2

  6. Texas A&M University

Reader Emails

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

Letter 1 – Bathroom Fly


Subject: Flying insect
Location: Nappanee Indiana
February 1, 2017 7:17 pm
I’m trying to identify a small winged insect about the size of a pencil eraser.
Signature: Dacia Reid

Bathroom Fly

Dear Dacia,
Based on this BugGuide image, we are confident this is a Moth Fly in the subfamily Psychodinae, the group that contains a common household pests known as Bathroom Flies which according to BugGuide are “often found around sewage installations, in public washrooms, and bathrooms in homes, and are attracted to light; larvae live in organic sludge that forms on inner surfaces of drains and sewage pipes; pupae occur on the surface of the organic film that the larvae have been living in.”

Letter 2 – Bathroom Fly


Subject: Bug in south florida
Location: South florida
May 27, 2016 4:14 pm
I just need to know what big this is. Every once in a while I see these in my bathroom. I live in south Florida
Signature: Rick

Bathroom Fly
Bathroom Fly

Dear Rick,
The Bathroom Fly or Drain Fly gets its common name because the larvae develop in the sludge that forms in plumbing.  Your submission will go live in June while the editorial staff of What’s That Bug? is away from the office.

Letter 3 – Bathroom Fly


What Is This Fly?
Location: Toronto, Canada
May 18, 2011 8:14 pm
I work in a medical office on the second floor and we have large windows. There are a few houseplants at the window. I noticed these small flies every day. They keep coming from somewhere, but our windows don’t open so they may live inside the building. They are very sluggish, I can pick them up with my fingers or hands. They don’t fly away like normal flies. I find many of them sitting by the window, usually dead and drying up. I can’t seem to figure out what they are, and where they are coming from. Can you please help?
Signature: Eddie

Bathroom Fly

Hi Eddie,
This is an amazingly detailed image of a Bathroom Fly.  Bathroom Flies breed in the sludge that accumulates in drain pipes.  They are also called Drain Flies or Moth Flies.

Letter 4 – Bathroom Fly


Subject:  What type of fly is this
Geographic location of the bug:  Staatsburg,ny
Date: 09/09/2021
Time: 08:49 AM EDT
Your letter to the bugman:  What fly specie is this I’m 73 , never saw this before.
How you want your letter signed:  ?

Bathroom Fly

This is a Bathroom Fly or Drain Fly in the Moth Fly subfamily Psychodinae, a group that is considered an annoyance to many home owners and tenants because Bathroom Flies breed in the sludge that forms in indoor plumbing.  According to BugGuide:  “Adults often found around sewage installations, in public washrooms, and bathrooms in homes, and are attracted to light; larvae live in organic sludge that forms on inner surfaces of drains and sewage pipes; pupae occur on the surface of the organic film that the larvae have been living in.”

Letter 5 – Bathroom Fly


Identify this Fly?
Hi! Found your website while trying to ID this tiny fly that is in the attached photos; we live in Miami, Florida, closer to the Everglades than the ocean, and have noticed an increase in the number of these guys (gals?) in our home. They are completely black, very little shiny to them; they are rather slow flying when compared to common house flies, and are typically found on the bathroom walls, which we guess is because they like humidity. Any ideas, and, should we be concerned? Thank you for such an interesting website.
PS: Macro fotography of insects is harder than I thought!!!

Hi Louis,
Your macro-photos of the Bathroom Fly, Clogmia albipunctata, one of the Family of Moth Flies, Psychodidae, are quite good. As you indicated, they like damp areas, and are often found in bathrooms indoors and near stagnant water and cesspools. The larva live in the much found in drains and dead-flow areas of household plumbing.

Letter 6 – Bathroom Flies Mating


Can you identify that bug?
In my house, we have a bug problem! We can find lots of the bugs I’m sending you, we had found two sources but they disapeared just a few days! They come from very black thin worms and larvae open to make them live. The source need water! Please help me! Amicalement,

Hi Cinci,
These are Bathroom Flies, Clogmia albipunctata, and one image shows a mating pair. They are often found indoors in bathrooms and the larva live in sludge in the pipes and drains.

Letter 7 – Bathroom Fly


Location: west coast Tampa Florida
January 21, 2011 8:52 pm
I find these in my bathroom only. The bathroom has a exhaust fan in the ceiling and a drain in the shower. The size is between an eighth and three sixteeths of an inch.
Signature: Thanks in advance

Bathroom Fly

Hi Richard,
Interestingly, you had all of your answers built into your submission.  This is a Bathroom Fly in the Moth Fly (how you labeled your photo) family
Psychodidae.  They breed in the sludge that forms in pipes and the adults can become quite plentiful in rooms with plumbing that needs to be cleaned out.


  • 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.

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  • 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.

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23 Comments. Leave new

  • I have these gross bathroom flies, but never had them until my husband put in a new shower.
    please help I am at my wits end

  • Thank you so much for this post! When I lived in Rio de Janeiro, Brazil I used to see those all the time in the bathroom. I thought it was some kind of harmless tiny mosquito. Now I know what it is called 🙂 So what do they eat anyways?

  • how do i get rid of these annoying bathroom flies!! they are driving me crazy

  • I just make few traps, and get rid of drain fly)

  • We have had these little bugs for 2 years, and we think we just got rid of them. It took 2 days. I poured Pectracide Bug Stop (indoor plus outdoor)
    down all our drains (bathroom sinks and bathtub, shower and sink in 2nd bathroom, kitchen sinks). one cup for each drain. We quit seeing them yesterday, except for a few who we think have died now of old age. They definitely are breeding in the drains. Whenever we had to take a shower or bath, we replaced the spectracide when the water drained. The stuff costs about $7 at WM. I only used 1 jug which was 1.33 gal., but I bought another for maintenance.

  • Gross, I have these damn things flying all around. How the hell do I get rid of them?

  • Nicole Burzynski
    April 12, 2018 1:16 am

    Are these flys dangerous to humans ?

  • Steven Cimino
    May 28, 2018 3:15 pm

    When I was twenty years of age, I rented a house that had these flies. They would come up from the crawlspace through the ventilation ducts in the floor, probably attracted by the lighted area in the entry hall of the house. We would come home in the evening and six or eight flies would be on the walls waiting for us. When you went to hit them, black smudge on wall.
    When I inspected the crawlspace area, I found that there were numerous puddles of water always present on top of the plastic sheet that layed on top of the clay floor of the crawlspace.
    I knew then what the source of the flies were.
    I complained to the landlord. He did nothing and I lived with the problem for a year and then moved. Later I learned from the landlords wife that upon the new tenants moving in, an inspection of the crawlspace indicated the sewer pipe joint had failed…. raw sewage from the toilets in the house was seeping into the crawlspace. This is what created the environment for those bugs to grow. It was a very simple fix and I was sorry to hear later that I was right and had to live with that unsanitary condition because of a landlords ignorance of not taking me seriously.
    Anyone who thinks these flies are “cute”, do not understand that another way of saying “organic material” is ….sh*t. I call these “sh*t” flies and they are definitely not something anyone should live with.
    Now forty years later they have shown up in my house. From reading this, I am going to use baking soda and vinegar in my drains, especially the two floor drains in my basement. I poured bleach down the drains yesterday but the baking soda / vinegar will help break up and clear the “organic”material within the pipes and then I will flush with hot water.

  • Lisa Howard
    June 14, 2018 6:12 pm

    I found one of this in my hair ! Disgusting I guess it was flying around and got stuck in my hair somehow any advice on how to get rid of these things

  • I’m a full time RV’er and get these annoying creatures whenever I have the hose attached to a sewer. I’m able to use septic tank safe RV chemicals or I use bleach and the attachment on my garden hose to flush my tanks.
    But in a residential situation I would think an otc drain cleaner should suffice, or try vinegar lemon juice, and baking soda – but you’ll have to make it thick like pancake batter so it just creeps down the pipes and doesn’t get too thinned out in the p-trap.
    Good luck!

  • I’m 74 and live alone in Ohio how do I clean the drains out?

  • Wikipedia says they are harmless.

    But they are rather annoying when they buzz near your ear and leave a black powdery smudge on the wall when you squish them.

  • Wikipedia says they are harmless.
    (“Clogmia albipunctata” article).

    But they are rather annoying when they buzz near your ear and leave a black powdery smudge on the wall when you squish them.


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