We recently had a sewer fly infestation caused by having a cracked mortar collar on the rest bend of the soil stack which runs through the upstairs and downstairs bathrooms. I removed a good portion of the boxing-in in order to see what was going on and the rest bend was fixed and the drain relined by Dynorod. So, that seemed to make the sewerflies disappear. However, the boxing is still not replaced.

Around June time some different flies started appearing in the downstairs loo (same room). The numbers are still much lower than the sewer flies, which were in the 100s per day. These new flies are around 10 per day. However I cannot identify these flies. They are larger, longer bodied and darker than the sewer flies. Images attached.

Can anyone identify these? What is their life-cycle/food source? Are they just 'naturally' occurring flies that would be present in the underfloor space which have drifted in due to the boxing-in not being replaced?


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That's the tip of my index finger for scale. The flies are probably 4-6mm in length.

  • 1
    Those are space bugs. They come from Klendathu via meteorites. – Tyler Durden Sep 27 '15 at 16:38
  • @tylerdurden ok thanks that answers one question then. What should I do about them? – El Ronnoco Sep 27 '15 at 16:50
  • Would Mr or Mrs downvote care to comment? – El Ronnoco Sep 28 '15 at 10:06
  • 1
    bug identification is better suited for biology stack exchange – n00b Jan 31 '17 at 16:41
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    I'm voting to close this question as off-topic because it has nothing to do with home improvement. – Daniel Griscom Jan 31 '17 at 17:21

I just found this on the internet check it out it definitely is what you have. http://www.doyourownpestcontrol.com/drainflies.htm This site deals directly with drain flies and the other flies that might be mistaken for them in the same situation good luck let me know how it turned out.

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  • Hi, thanks for your answer. We certainly did used to have the sewer moths/drain flies. But they have been eliminated. I'm not sure which species these are, or why they have replaced the drain flies. Presumably they have a different food source. Do you think perhaps these are phorid flies? I don't know where they will be getting food from. – El Ronnoco Sep 28 '15 at 10:06

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