Are Drain Flies Harmful? Helpful Facts About Diseases Drain Flies Carry

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Have you ever noticed those little winged insects crawling out of your bathtub drain? Those are drain flies. These creatures have a very nasty reputation for dwelling in the most unsanitary conditions. That’s why some people would ask if they can be a serious threat to our health. But is this correct? Are drain flies harmful? Here are a few key details that can help you answer that.

Are drain flies harmful?

Drain flies are undoubtedly gross. But there are some cases where they can actually be harmful. CC Image courtesy of Sanjay Acharya on Wikipedia

What are drain flies?

Drain flies or sewer gnats (Psychodidae) are furry little flies that are found almost anywhere in the world. There are currently 2,600 species discovered worldwide, and most of them prefer to live in humid tropic places. However, in our own homes, we’d mostly see these tiny winged insects in their namesake, inside plumbing drains. You can also spot them in septic tanks, sewage systems and soil with sewage contamination in it.

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Psychodidae are very small, only measuring up to 1/8th of an inch or 0.32 cm. They also have various appearances, depending on their species. But generally, they’re often described as moth-like with furry short bodies and hairy wings with vertical lines in them. They have the colors black, grey or brownish grey. And they also sport antennae that have hairs sticking out on their sides, resembling a bunch of little feathers lined together.

Are drain flies harmful?

Most drain flies don’t carry immediate health hazards to us humans even though they come from places that we wouldn’t want to be near to. However, according to a 2015 study on Psychodidae infestations from Cambridge, there are special recorded cases that pointed to specific species of drain flies as the main cause or trigger for some diseases. These are myiasis, microfilaria and asthma.


The CDC describes myiasis as a disease that occurs when the body is infested by a parasite, namely fly larvae that need a host to develop. Just like a science fiction movie, the larvae would typically dig into the tissue of their hosts and feed on them, causing painful lumps, burning, itching and even bacterial infection.

While most domestic drain flies don’t have anything to do with this, according to the 2015 study, the species Clogmia albipunctata is an opportunistic agent of this particular disease.


The Sycorax silacea, is another tropical variation of the common drain fly. It’s a blood feeding fly that’s known to transmit parasitic nematodes. Specifically, Sycorax silacea is a vector of microfilaria.

Microfilaria is an early stage of parasitic Onchocercidae nematodes. These little invaders are microscopic worm-like creatures that thrive inside the bodies of their hosts. They essentially live inside in the tissue or circulatory system. Adult nematodes  periodically release their offspring, the microfilariae, into the blood to be picked up by the blood-sucking Sycorax silacea and to be transported into another host.

Having microfilariae in your system is called microfilaraemia. This can lead to fever, pain, and/or extreme swelling in certain areas of the body as well as many other painful symptoms.


Another tropical drain fly, the Phlebotominae, also feeds on blood. Through this, it’s able to transmit tropical diseases, particularly leishmaniasis which is another condition caused by parasites.

Parasites from the Leishmania can enter the body through the fly’s bite. From there, it can be present in one of three ways, via skin ulcers, ulcers in the skin, mouth and nose, or through fever, an enlarged spleen and liver and a low count on red blood cells. Human infections are the work of more than 20 species of Leishmania.



While it may sound totally unlikely, drain flies and even other small insects can cause bronchial asthma. According to PestProducts, if they grow in huge numbers, the wind can easily blow them towards houses. Inhaling the dust from these disintegrating small flies can possibly trigger asthmatic reactions.

How to Get Rid of Drain Flies

Even though common drain flies are not as harmful as the ones that we mentioned, they can still be pretty annoying to deal with. So to help you with that, we’ve gathered a few helpful tips to get rid of these gross flies.

  • Inspect all possible breeding grounds. Look for potential breeding grounds in your house and in other nearby drains. But while these flies typically spend their time in house drains, it’s also equally possible that they can come from a nearby area that’s polluted, like from another part of a sewer system or from a septic tank.

  • Clean the source. The only way to stop these bugs from invading houses is to clean the breeding ground. Contact the appropriate authorities if more than one home in a neighborhood is affected. A joint-effort on cleaning will prove beneficial for everyone.

  • Check the pipes. Sometimes, the pipes can break open and release the drain flies that live there. If you think that this is the case, watch out for drain flies coming out of the floor slabs. You’d most likely have to pry those slabs open to check.

  • Pour hot water down the drain. Incinerate the flies and their larvae with hot water. This also cleans some of that leftover gunk inside the drain.

  • Use drain cleaners. Many local brands are toxic enough for the flies. Just make sure to use the drain cleaner regularly and carefully. Keep them out of reach from pets and children.

  • Install fine mesh screens. Put mesh screens on top of your drains to stop the flies from entering your home.

So are drain flies harmful? Unlike the tropical drain flies, the usual flies that we often see in our homes aren’t that threatening when it comes to our health. They’re not at all deadly. But of course, who wants to live with dirty sewer insects anyway? So for your peace of mind, getting rid of them is still the best option.

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