Insects are everywhere, and without a doubt, there are several within a few feet of where you are located right now, even if you can’t see a single one. This might not bother you, but if you see visible evidence of bugs, it might be a little more disconcerting, and even more so if they are right in your face.
One bug that some homeowners have trouble keeping away are sewer gnats.
These can easily be mistaken for a fruit fly, but when closely observed, you will notice several details about them that are different. The wings of sewer gnats are very dark, and when swatted, they will leave behind a black dust, even when not hit.
Sewer gnats live, as the name implies, in your sewer, and they are difficult to get out of there. They can withstand many chemicals, and even boiling water won’t necessarily remove their nests. Your best bet is a mechanical cleaning of your pipes, using a snake or a similar device.