Are Drain Flies Harmful?

Have you seen any pesky little drain flies around your house lately? With their small, dark bodies and spread-out wings, they look similar to moths and love breeding in damp places like bathrooms, drains, and kitchen sinks. 

Their presence can certainly be a nuisance and give the impression of unsanitary conditions, but the real question is whether they are harmful or not. Let’s dive into this—read on to find out what exactly drain flies are and whether they are harmful to humans!

What Is A Drain Fly?

Drain flies are a family of true flies, and their scientific name is Psychodidae, but they are also commonly called filter flies, sewer gnats, sewer flies as well as moth flies because of their moth-like appearance. They have small, dark grey fuzzy bodies and are smaller in size than typical houseflies, around one-fifth of an inch. 

The name ‘drain flies’ comes from the fact that these insects inhabit places that collect sewage and bacteria, such as bathroom drains, bathtubs, showers, sinks, filters, sewers, sewage treatment plants, and facilities that process waste, etc. In houses, they are most commonly found buzzing around in bathrooms, especially near the sink or floor drain.

They may also be present in basements, septic tanks, wet garbage cans, contaminated soil, or basically, anywhere there is water standing stagnant for some time, such as an unused toilet or sink.

This is because drain flies feed on organic matter that is present in sewage and wastewater and lay their eggs in standing water. Drains are an optimal place for these flies to live and reproduce in, so you may commonly find them in or around drains in your bathroom or other places inside your house.

Are Drain Flies Harmful?

Drain flies are not harmful in most situations, especially if they are not present in large numbers and clusters. These flies are attracted to the smell of rotting food, sewage, and other organic material, and they can be a pest as they will fly around your house, but they do not bite or sting. However, there are some cases in which drain flies can be harmful:

  • Present in Large Numbers

Drain flies can reproduce quite fast and lay hundreds of eggs in their nest in just a couple of days, which means that an infestation can come on quickly, and you will need some costly and persistent measures to get rid of the problem completely.

A few flies in the bathroom are harmless, but if their population seems to multiply rapidly and they cluster around and block light sources, you know it’s time to remove them.

  • They Carry Bacteria

A large number of drain flies in your kitchen can pose a health hazard as they are attracted to rotting food and carry bacteria wherever they sit. This means that they could transmit disease-causing microorganisms and make both people and animals in the house sick.

  • Can Aggravate Asthma

There have been some reports that an abundance of drain flies may aggravate the symptoms or cause respiratory asthma in people who accidentally inhale the insect fragments. Although there is not a lot of research proving this, it is better to err on the side of caution and eliminate drain flies from your house if you or anyone from your family suffers from asthma.

  • May Cause Parasitic Infection

Drain flies may also act as opportunistic agents for parasitic infection (myiasis) as they are attracted to infected or open wounds and can produce larvae there. Although this is not a major risk, it is important to clean and disinfect wounds regularly and keep them covered.

  • Other Diseases

Overall, the type of drain flies that are usually found in bathrooms are not a significant health concern, and their presence in small numbers is not a cause for alarm. However, certain subspecies can carry tropical diseases or transmit microfilaria to humans.

If the drain flies nest and causes an infestation in your house, it is better to be on the safe side and have them removed by a professional pest control company.

Are Drain Flies Harmful To Humans?

Drain flies are not really harmful to humans in smaller numbers, but the buzzing sound they make as well as the sight of their dark moth-like bodies can be irritating for you and your family members—as well as a source of embarrassment if you any guests over.

Drain flies do not bite or sting people or animals, but they can be a nuisance because they tend to swarm around people’s heads when someone is doing dishes or taking a shower.

For the most part, they are harmless, even though you might feel inclined to think otherwise since they inhabit drains and feed on sewage and garbage.

Keep in mind that drain flies have not been associated with carrying human diseases or significantly impacting the health of humans living in the vicinity. The real problem arises when drain flies rapidly multiply within a short time and grow in large numbers, which is especially dangerous if they are near a kitchen as they could contaminate food.

Should I Get Rid Of Drain Flies?

Although drain flies are harmless if they are few in number and not a nuisance for you or your family, you should consider removing them if their population starts to multiply and grows out of hand.

Since they can reproduce considerably in a short span of time, it is important to keep an eye on the number of drain flies in your house and act fast if signs of an infestation appear.

Apart from being a nuisance, a large number of drain flies could be a health hazard, and you need to get rid of them. First, determine the source of these pests by finding out where they have made their nest. Check any drains, sewage pipes, sinks, and tanks in your house that have contaminated or stagnant water.

Since it’s tricky to completely get rid of them on your own, contact a professional pest control company to handle the problem for you.


Are Drain Flies Harmful to Dogs?

There is no significant evidence that suggests drain flies are harmful to dogs or transmit parasites or diseases. However, your dog might be tempted to go after or eat them, which can pose a health risk since drain flies inhabit sewage-contaminated areas. Read more about it here.

Will Bleach Kill Drain Flies?

Bleach might kill some of the larvae of drain flies, but it will not completely get rid of them and isn’t a proper solution if you have an infestation. Furthermore, it might even damage your drain pipes. You can find out more about it in this article.

Can Drain Flies Make You Sick?

It’s possible that drain flies could make you sick by spreading bacteria from one area of your home to another. However, there has also been signs that drain flies can trigger bronchial asthma in susceptible individuals.


In short, drain flies are mostly harmless for humans and pets but can be a problem if they nest and multiply rapidly. 

Although they have not been associated with transmission of any major disease or identified as a health risk in smaller numbers, the presence of drain flies might aggravate the symptoms of bronchial asthma in some people. They are also capable of causing parasitic infection in humans, and some types might also carry tropical diseases.

However, you don’t need to panic if you find a few drain flies in your bathroom as they are not harmful in smaller numbers. But in case you have an infestation on your hands, take action immediately!

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