16 June 2025

It’s that time of year again when the house warms up and more insects appear indoors. In the past week I’ve seen one drain fly on the shower wall every other day. I’ve swatted each one but by yesterday I’d swatted a total of four. That’s it. I am done with observing Nature in the bathroom. Here’s what these flies are and the advice I’ve found on how to get rid of them.

The bathroom moth fly (Clogmia albipunctata) is a true fly with a worldwide distribution, thanks to humans. It spends most of its life perched on walls and is often found in the bathroom because it breeds in the drain. About 1/8 inch long, it has brownish and blackish hairs on its wings and body which give it a moth-like appearance when seen up close. It is a weak flier and very easy to swat.

The Univ of California Integrated Pest Management Program explains:

“Female moth flies lay eggs in moist to nearly saturated organic matter. In an urban environment, moth fly development often occurs in the slimy organic matter coating sink or shower drains, giving these flies an alternate common name “drain flies” used by many pest management professionals. However, moth flies may also be found developing in wet animal manure, sewage or even compost.”

“Once the eggs have been laid, they hatch in about 48 hours and continue to develop in the wet organic matter as larvae. Moth fly larvae in the final (third) larval stage are approximately 1/4 inch in length, have a distinct head, and a siphon on one end, which allows them to breathe in the wet environment. Immature flies pupate at their developmental site before emerging as adult flies. The life cycle of moth flies can be completed in as little as 8 days but can take as long as 24 days depending on temperature.”

Here’s a video of their larvae.

Bathroom moth flies are useful in water purification at sewage treatment plants. They are also a good food source for insects, fish, birds, reptiles and amphibians in every stage of their development.

But they are not useful in the bathroom so how to get rid of them?

Clean the drain.

Most poured-in remedies do not kill these hardy critters because they are able to hide. You have to remove their breeding site by getting rid of the organic matter in the drain.

See Univ of California IPM Program: Moth or drain flies for the real “how to” answers, some of which are listed below.

• Boiling Water will not get rid of the flies. It will loosen the organic matter but not completely wash it away. (See comments for the correct recipe.)
• Bleach will not get rid of the flies. They hide.
• Baking soda and vinegar may loosen the organic matter but will not get rid of the flies.
• Commercial drain cleaner such as Drano may help with the organic matter.
• Biological drain cleaner (I’ve never used one of these)
• This works: Clean the drain with a bristle brush & wash it away. Call the plumber.