Got him! (or perhaps her)

[urbpan]

I was summoned to one of the office buildings I service to respond to complaints of a small fly (everyone described a single fly) bothering people as they worked. I inspected trash cans and recycle bins for fruit fly breeding conditions, I inspected potted plants for fungus gnat breeding conditions, and I checked air conditioners for signs of phorid flies.
I found nothing, but left some folded glueboards near some work stations, on the off chance the offending fly would land and get itself stuck.

After I left, the fly returned and started bugging a coworker at her desk. She remembered the glueboard and swatted the fly with it, catching the black-bellied dew-lover as you see it above. This is almost certainly Drosophila melanogaster (translated into English in the previous sentence), the common fruit fly (vinegar fly), a cosmopolitan pest and perhaps the most important lab animal ever used. I was informed another time that I posted about this fly that the scientific name is probably no longer valid, but owing to its appearance in literally tens of thousands of scientific papers, it is not likely to change soon.

I've received no further complaints from this office building, but that is probably due to the weather. My theory is that the flies were breeding just outside the office doors, but the cold snap has put that activity on hold.