Drain flies are pretty common pests. They can be found in temperate, subtropical, and tropical zones as well. Drain flies are well adapted to the human environment and they often appear in bathrooms, kitchens, and other places where water is continuously present. Besides causing a lot of annoyance, their presence sometimes also raises health concerns.
So it’s best to get rid of drain flies as soon as you can for several reasons. How can you do that?
First, you have to eliminate their eggs and larvae by thoroughly cleaning the potential breeding sites, such as sink overflows, bathroom drains, and leaky shower pans. Then you have to get rid of the adult drain flies using natural sprays, sticky traps, or other effective methods. You also want to make sure you take some preventive measures to avoid reinfestation.
Although there are many methods out there, they’re not equally effective. In this article, I’ll show you the best ways you can get rid of drain flies fast and permanently, without wasting your time.
Let’s get started!
Make Sure You Are Dealing with Drain Flies
Drain flies (also known as moth flies, bathroom flies, sink flies, filter flies, drain gnats, and sewer gnats) are small moth-like insects. Quite a few drain fly species exist, one of the best-known ones is called Clogmia albipunctata. This species is the one you will most likely meet in your bathroom and kitchen, and that causes the most trouble in hospitals and other institutions.
How to Identify Drain Flies
If you want to get rid of drain flies, the first task is to identify them. They’re often confused with fruit flies, however, it’s pretty easy to notice the difference between them if you know what to look for. If you’re sure you’re dealing with drain flies, skip this part and jump to the next section.
Drain flies typically infest drains, sump pump pits, and sewage systems, thus in homes, they usually can be found in bathrooms and kitchens. They need humid places for breeding because their larvae live in aquatic habitats and feed on bacteria.
Sinks and other moist places with organic debris in and around the house are perfect environments for the larvae of moth flies. Females breed only once in their lifetime and usually lay 200-300 eggs that hatch into larvae within 48 hours. The larval form of drain flies is mostly transparent, and approximately 0.16-0.20 inches (4-5 mm) long, therefore it’s not easy to discover. The larval stage usually lasts up to 24 days, and the adult drain flies live for approximately 15-21 days.
What does a drain fly look like?
An adult drain fly usually has a length of 0.12-0.20 inches (3-5 mm) and it’s very similar to a small moth because its body and wings are covered with thick hair. That’s why it’s sometimes also called moth fly (1).
Drain flies usually have a dark color (mostly black, sometimes brownish) and segmented antennae. Clogmia albipunctata (a common species of drain fly) has also got some small white spots on the edges of the wings (hence the name).
Drain flies are more active at night. They’re weak fliers, thus they usually spend most of their time on walls. That’s the reason why they can be caught much easier than house flies. And now let’s see what’s the difference between drain flies and fruit flies, and how you can distinguish them.
Drain Flies vs. Fruit Flies
Drain flies are most often confused with fruit flies. Although they’re very similar in size, there are some unique characteristics that make it possible to easily differentiate them.
- First, the body and wings of fruit flies are not covered with thick hair (there’s some tiny hair on them but that’s not visible to the naked eye).
- Second, fruit flies are yellowish and lighter in color than drain flies. Also, drain flies often seem to be more robust than fruit flies.
- And then there are the antennae: while drain flies have long, segmented antennae, fruit flies only have tiny, hardly visible ones.
Get Rid of Drain Flies In Two Steps
So how do you get rid of drain flies once they appear? The good news is that if you know what to do, in most cases you can successfully (and permanently) eliminate them without much hassle. Let’s see the methods that are tested and proven to work.
Note: If you want to get rid of drain flies fast, you must eliminate their eggs, larvae, and adult forms as well.
FIRST STEP: Get Rid of Eggs and Larvae of Drain Flies
The first thing you want to do is find and eliminate the breeding sites of drain flies. Eggs and larvae are not easy to drown. They’re highly resistant to heat and most water-borne chemicals, including bleach.
The most reliable method to eliminate them is to clean the potential breeding sites from all the organic debris and slime. This way you can hit two birds with one stone: you deprive larvae of food so they’ll die before turning into flies and you prevent adult moth flies from finding suitable places for laying their eggs.
How to find breeding sites?
The larvae are hard to discover because they’re small and highly transparent, so you’re better off looking for the places where the adults come from.
Drain flies need humid places and organic material for breeding. You can either place a glass jar over the drains or cover the overflow outlets with adhesive tape to check where the drain flies are coming from. Leave the jar and the adhesive tape on the outlets for at least 24 hours so that you’ll get a clearer picture of the severity of the infestation.
You can find a ton of helpful information on how to identify all the places where drain flies are coming here.
Make sure you check and thoroughly clean:
- Sink, shower, and floor drains and drain pipes
- Leaky shower pans
- Kitchen trash cans
- House plant bases
- Areas under loose floor tiles
- Condensation pans under the refrigerator
- Wet organic materials in and around the house (including the basement)
- Unused toilet tanks
- Sump pump pits
- Rain barrels
Drain flies often lay their eggs in multiple places, so make sure you check each place that can serve as a breeding site.
How to clean drains and other breeding sites?
For mechanical cleaning, you can use a stiff wire brush and a drain snake. Make sure you eliminate all debris from inside and the wall of the pipe.
In most cases, there will be places you can’t reach with a brush. That’s why, for the best results, I recommend you also use some kind of enzyme drain cleaner, such as InVade Bio Drain Gel, InVade Bio Foam, or Forid Drain Gel Cleaner. These products remove the organic buildup in drains naturally so they help to destroy the breeding sites of drain flies.
As an alternative, you can pour drain cleaning gel into the drain. Let it sit for 30-60 minutes and flush it with hot water. Often you have to repeat this process a few times to get rid of all the organic matter in the pipe.
If you prefer using natural methods, you can pour baking soda (2-3 tbsp.) and then a cup of white vinegar into the drain. Wait an hour and flush the drain with hot water. If you suspect that the infestation is located deep in the pipe, you’ll have to double or triple the amount of baking soda and vinegar and repeat the whole process a couple of times. In fact, we have a full guide on how you can clean your dirty drain pipes and slow-draining sinks naturally with homemade cleaners.
Removing the debris and slime is usually enough to prevent drain flies from breeding, however, in certain situations (for instance, in the case of large infestations), you may want to inhibit the remnant larvae to turn into adults. For that purpose, you can use an insect growth regulator (IGR), such as Gentrol IGR Aerosol, which should do the job for you. IGRs won’t let larvae molt into the next stage and also prevent eggs from hatching.
Note: Avoid pouring insecticides into the drain, except for those that are certified for this kind of application. Always read the instructions on the label of the product you use.
Again: It’s very important to mechanically and chemically remove all the organic debris and slime from all the potential breeding sites to cut off the food supply of the larvae and prevent adult drain flies from laying their eggs.
Cleaning the drains thoroughly is usually enough to eliminate the actual infestation. However, it’s highly suggested to clean them at regular intervals to prevent future re-infestations.
SECOND STEP: Get Rid of Adult Drain Flies
Now that you’ve eliminated the breeding grounds, you also have to get rid of the adult drain flies. If you skip this step, you give the flies a chance to find new breeding sites where they can lay their eggs. If that happens, you have to start the elimination process all over again.
How to kill adult drain flies?
- Using a fly swatter. Fortunately, drain flies are not as good at maneuvering in the air as normal flies and they’re much slower as well. They spend a lot of time sitting on the wall (especially during the daytime) where they’re easy targets.
- Using natural sprays, such as Terminix SafeShield Natural Indoor spray or Pyrid aerosol. Both contain natural ingredients and can be used indoors and outdoors as well.
- Using sticky traps, such as Musca-Stick Jr. It attracts drain flies with pheromones, and when they want to land unseeingly on the orange-colored trap they get stuck. Musca-Stick Jr. has no odor and contains no insecticides. It’s easy to install and use, however, you should place it out of reach of children and pets because it’s really very sticky.
- Using natural traps. If you prefer home remedies, mix a cup of apple cider vinegar, half a cup of sugar, and a few drops of dish soap in a bowl and place it close to the infested area. The dish soap breaks the surface tension of the liquid and when flies try to land they simply sink. Note that this method doesn’t always work with the same efficacy and I haven’t really found the exact reason for that.
The high survival rate of drain flies in homes is partly due to their behavior in the presence of light: they’re not attracted to light (many websites claim the opposite, however, studies show they’re wrong) and you can’t catch them all by using UV light either because more often than not they simply don’t care.
So don’t have high expectations if you try a UV insect light trap, you can be sure you’ll have to apply additional methods to collect and kill all drain flies.
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Prevent the Return of Drain Flies
Unfortunately, drain flies can return if they find favorable conditions for breeding in or around your house. If you want to get rid of drain flies for good, you have to take some preventive measures. Remember: prevention is always easier than elimination.
Let’s see some measures that will help you to prevent drain flies from reappearing in your home:
- Make sure there is no standing water in your home (including drain pans and house plant bases).
- Keep your drains and pipes clean and free of slime and organic buildups.
- Don’t leave any moist organic matter in the trash can.
- Make sure the kitchen sink is free of food waste.
- Repair leaky appliances.
For more details, check out this guide to stop drain flies from coming back to your home.
Are Drain Flies Harmful? Do They Pose a Health Risk?
Drain flies are usually harmless but annoying pests, especially if you have to deal with a large infestation.
However, in some rare cases, their larvae can cause a parasitic infection, called myiasis that has different forms: urinary, nasal, intestinal, etc. Drain fly larvae can cause all of them, however, you’ll find only a very limited number of cases in the literature (2).
Like most flies, drain flies can also serve as vectors of bacteria. This is a greater concern in hospitals where drain flies can transmit bacterial pathogens associated with nosocomial infections (5).
Putting It All Together
As you can see, getting rid of drain flies is totally doable if you follow a tested plan. Don’t forget that you must eliminate the breeding grounds and the adult moth flies as well, otherwise, you will only see a temporary drop in the number of pests. Check and clean thoroughly and regularly all the places where both moist and organic materials can be found to avoid reinfestation.
The methods mentioned in this article will work in the vast majority of cases. However, if for any reason you can’t succeed in getting rid of moth flies or there’s a large infestation, consider using a professional pest control service.
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