What I've Learned: Sphaerocerid flies look like fruit flies, but ain't fruit flies
Over the holiday season I had a gross fly infestation in my basement office. They looked like fruit flies (which are occasionally called vinegar flies, because they are drawn to cider and wine vinegar, as well as fruit and other sugary messes), but were totally uninterested in stuff fruit flies love. After *a lot* of very frustrating research, I narrowed the ever growing hoard down to being one of the 240+ species of North American sphaerocerid flies.
In general, sphaerocerid flies are more of an industrial problem (like in morgues, industrial kitchens, and sewage treatment pants) than a home problem (there isn't even a consistent common name for them), so tracking down info was immensely frustrating.
I have officially vanquished these bastards. Here's the skinny:
Sphaerocerid flies look a lot like fruit flies: they are roughly the same size, but their eyes are smaller, and bodies darker. They are sometimes called "drain flies," but this is misleading, as the much more common (and less annoying) moth fly is also called a "drain fly." Both sphaerocerids and moth flies feed on "decaying organic matter," such as kitchen scraps, poop, or corpses; they usually infest the elbow joints in kitchen sinks, or floor drains that feed into the sewer system.
Our infestation began after we had a minor basement flood, which apparently backed some poopy water into our perimeter floor drain (which sort of like a storm-water gutter, running along the inside wall of our entire basement; it's entirely separate from the house's sewer/greywater system, and was installed to prevent rainwater and snowmelt from flooding the basement through cracks in our foundation). The infestation was confined to my office (which is good), but involved thirty running feet of enclosed, gutter-style drain, buried in concrete and accessible only via a quarter-inch opening along the foot of the wall (great for tiny flies, a bitch for me). Also, it was really, really gross, because there were A LOT of flies. Like, enough to coat the little basement windows.
You can't wash these guys down the drain; they are tenacious and can successfully feed and breed in just a little film of grease. Full-strength bleach does nothing (I went through several quarts). The only option is to remove their food supply.
I spoke to a lot of exterminators, who mostly had no idea what I was talking about. Exterminators, as it turns out, are highly responsive to perturbations in the real estate market; many of the places I called had gone out of business (or, in the least, their phones had been disconnected), the remainder had cut staff and hours, and all of were sensitive to the fact that their services are expensive and outcomes not guaranteed. One suggested I get an indoor fogger-style bug bomb (which kills just about anything, including pets and children), do it myself, and save the money on a house call. Finally I came across a little Detroit-area shop that does residential and commercial work, knew exactly what I was talking about, and was willing to sell me chemicals out of their stock, basically at cost.
The solution: Enviropro DF5000. This stuff is basically anti-freeze holding a suspension of crazy ass bacteria that devour whatever yuck it is that the flies are infesting. Additionally, either the chemicals (which have wicked-weird fumes that make your chest feel tight and cooky) or the bacteria do something *very unpleasant* to the flies' central nervous system; for weeks I found them convulsing all over of the house.
But, after about a week of pouring a few ounces through a funnel and into my long floor drains every night (and wearing a respirator while working in my office during the day), the flies were notably on the decline. A month later the fumes have finally cleared, and the flies remain of blessed memory.
Google, I offer this data unto you, so that you may help the grossed-out, infested masses in defeating their arthropodal nemeses. Amen.