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A Drain Fly's Happy Place Is Down Your Pipes

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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.


Ever wonder where those little insects crawling around your bathroom came from? Bad news: your drain.

With all that fluffy hair, it looks like a tiny moth. And some do call it a moth fly. But a fly it is … a drain fly.

It’s called Clogmia – how appropriate.


It grew up over several weeks, out of sight, among things you thought you’d washed away.

Drain flies sneak in from the outside, through a crack in an old pipe, for example, to sip some water they sensed with this long mustache – their maxillary palps.

And here, on the plentiful gunk in your pipes, they’ll grow a family.

Welcome, little one! The larva is the length of an eyelash.

That gunk it lives in? Those are bits of you: hair, saliva and food. They make a nice meal for bacteria and fungi, which form this dark, living slime called a biofilm. This is what the larvae feed on. It also keeps them well moisturized.

If the larva ends up submerged, it can still chow down. It sweeps slime particles out of the water with a hairy mouthpart called the labrum and rakes them in with its mandibles.

Underwater, it breathes with a bubble on its backside that it collected at the surface.

This allows it to venture through deep pools in your pipes.

When larvae, or the more grown-up pupae, like this guy here, end up in a toilet bowl, it can be a shock. You might think the squigglers came out of you. Ew! Don’t worry – they can’t live inside us.

And even though the drain flies in your bathroom muck around in bacteria, they don’t really spread it to humans. They’re not interested in landing on us. Or even leaving the bathroom.

They’re in their happy place. When you wash your hands? They protect themselves from the water with their hairy wings. Each hair has ridges that trap air so the drops roll right off.

And if they’re caught off-guard by a sudden surge, the flies skate across.

But they’re not invincible: When they get trapped underwater long enough, they can drown.

If you find you really need to get rid of them, drain cleaner helps, but it won’t keep them away forever. There’ll always be some slime left behind, deep in your pipes, that could attract the flies again. So, if they want it, why not let ‘em have it?

Hi. Laura here. Did you know that flies have a secret set of limbs beneath their wings? No? It’s one reason they’re so hard to swat. Watch that episode next! See you there.

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