Why Does This Fly Live in Your Bathroom? | Deep Look

Ever wonder how those tiny, jumpy flies got onto your bathroom wall? Well, they came out of your sink drain after growing up down in the pipes. A goofy, long “mustache,” fuzzy wings and some aquabatics help them survive in that soggy environment.

DEEP LOOK is an ultra-HD (4K) short video series created by KQED in San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.
---

Drain flies are also known as moth flies because they look like miniature moths. One of the most common species of drain fly is Clogmia albipunctata, which has white markings on its dark legs. This is the species we filmed for our video.

Drain flies sneak in from the outside, often through cracks in old pipes. They lay their eggs in the slime inside the pipes. When larvae hatch out of the eggs, they feed on this living slime, which is called a biofilm. It’s made up of bacteria, fungi and other microorganisms that grow on the hair, saliva and bits of food that get washed down a bathroom sink.

---Why do drain flies show up in a house?

Entomologist Greg Curler, who studies drain flies, said they crawl into old buildings through pipes that rusted through, or cracked as the ground shifted. The flies use their antennae to sense the gases coming off the biofilm that has accumulated over time inside the pipes.

“The flies can detect the gas from a very long way,” said Curler, “and are attracted to it.”

---Do drain flies spread bacteria?

Even though they grow up as bacteria-eating larvae down in the pipes below your sink or toilet, the drain flies in your bathroom don’t spread bacteria around. That’s because they’re unlikely to land on you or your toothbrush or food. They’re not looking to eat your food or lay their eggs in it, the way that houseflies and blowflies do. Adult drain flies don’t really eat – they only drink a bit of liquid. And they pretty much stay put. They only fly afar when they need to find a new pipe to lay their eggs in.

---How do you get rid of drain flies?

Drain cleaner might get rid of drain flies temporarily. But the biofilm that attracts drain flies to the inside of pipes is hard to wash away, said Matthew Fields, who studies biofilms at Montana State University.

The microbes in the biofilm produce a sticky slime of proteins and carbohydrates that surrounds and protects them.

“Scrubbing the biofilm is the best way to get rid of it,” said Fields.

Since the insides of pipes where drain flies reproduce are typically out of reach for a good scrub, some biofilm is always there to draw the flies back.

---+ Find a transcript on KQED Science:

---+ More great Deep Look episodes:

Take a Deep Look at Your Roommates playlist:

Varroa Mites Are a Honeybee’s 8-Legged Nightmare

How Ticks Dig In With a Mouth Full of Hooks

---+ Shoutout!

🏆Congratulations🏆 to these 5 fans on our Deep Look Community Tab for being the first to correctly answer our GIF challenge! The word we were looking for was "biofilm." This viewer got the exact word:

@Axqu7227

And these fans did not use the specific term, but correctly described the elements of the biofilm:

@sheetals.1912
@jkresinartsandsuppliers6810
@Terra2000Z
@gracechen7393
@pranavr4017

---+ Thank you to our top Patreon supporters ($10+ per month)!

Burt Humburg
Max Paladino
Karen Reynolds
Daisuke Goto
Chris B Emrick
Tianxing Wang
Wade Tregaskis
David Deshpande
Laurel Przybylski
Mark Jobes
Carrie Mukaida
El Samuels
Jessica Hiraoka
Jeremiah Sullivan
Noreen Herrington
Louis O'Neill
Levi Cai
Elizabeth Ann Ditz
Titania Juang
Laurel Przybylski
Roberta K Wright
LAUREL PRZYBYLSKI
Mehdi
Jellyman
Syniurge
KW
SueEllen McCann
xkyoirre
TierZoo

---+ Follow Deep Look and KQED Science on social:

---+ About KQED

KQED, an NPR and PBS member station in San Francisco, serves Northern California and beyond with a public-supported alternative to commercial TV, radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios and the members of KQED.
#drainfly

[zapticuno]

Man they're such cuties!! And hey, they don't do harm, so it doesn't hurt to leave them be! I've seen them a few times, silly little guys they are <3
Does make me wonder though, how would these guys have lived before plumbing came to be? Because while they no doubt have adapted to life within our pipes, they must've come from something (or well, maybe not come from, but they themselves simply altered their lifestyle) that made the transition from outdoor life to life in our drains...

[Infernoraptor]

I had a big issue with these a year or so ago. It wasn't so much that they were flying around so much as they'd be attracted to the water in my refrigerator's ice maker and then freeze to death in there. Every ice cube had flies in them until I got drain cleaner and flypaper

[TatsumiOga]

I always did wonder what these insects were. This is why I love this channel!

[mushuwu]

I read "your pipes" and for a horrifying second I thought it was something that lives in your throat. Thank you for instilling a new phobia.

[echelus]

I have been observing these little fellas around my bathroom sink for years. I had never considered how their fuzzy wings could help them adapt to their environment!

[aramzyf]

i love these flies. because all they do is nothing in my bathroom walls. i call them the "npc fly"😂

[HaliphronA]

Always had some of this guys buzzing around an aquaculture lab I used to work in. I thought they were actually moths at first! Really cool to learn why I always found them there. Lots of organic waste and water.

[cryptbeast]

The fly family is the craziest group of insects. They've taken over just about any niche you can think of. The variety of body forms is very cool.

[FolkloreLover]

I’m a pretty clean person so I always wondered where these strange flys came from. The weren’t fruit flys or the ones that would come from my potted plants so it was always a mystery. Thanks for letting us know.

[zoushaomenohu]

Bogleech said it best: "A few tiny, flying soot balls in a bathroom hardly constitute a "pest problem" most people should be worried about, and if you happen to see one, I think you should if anything be glad to share your space with nature's tiny plumbing fairies."

[instantamazon]

I get these in my bathroom from time to time and they are so cute I just leave them alone. Thanks for putting my gunk to good use, kids!

[attila]

No wonder spiders move into my bathroom, it's free food for them.

[ivy_]

Saw this and instantly clicked. Probably my favorite "pest" insect

[gooeykit]

this is my favorite bug, when i took a CAD class last semester we had to make a decorated box and these was a drain fly on that. on tumblr im the most well known drain fly fan with my own tag for it. ive spread the love for drain flies amongst my friends. i have a drain fly pin and once i buy more beads i plan to make a drain fly perler. i have a really bad scientific journal thingy about drainflies where they didnt edit out the actual parts of the scanner machine and the text is like a milimeter big. i take it with me everywhere i go. im not even that smart and cant understand most of it but i really love this bug. this video rocks because it has drainfly footage with such high quality.

+they have the cutest pupa with bunny ears!!! its really awesome and it makes me sad that other ppl dont like them bc they arent harmful besides allergies and there are some rllly pretty pics of them ive seen. its so cool

[III---III]

These flies were the bane of my existence when I lived in a ground-level apartment that had 12 units per building sharing sewage.

[MrShoward]

I have always wondered what those things were! Thank you for the information!

[talmarit]

Wow. Since a child I’ve always thought these were moths. It’s fascinating how they can live in such an environment but also disgusting how they crawl through and eat that drain slime. The more you know, thanks deep look.

[paxcaster]

i randomly saw some small wigglers in a toilet once (that hadn't been used in weeks) and never found out what they were, it was one of the most mysterious and confusing incidents until now

[Koekie]

Fascinating!
I always wondered where they come from
Great channel as always ❤

[marckid]

I used to call these things Toilet Fairies as a kid lol