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