This isn't gardening related, but it was so effective, easy and frugal I thought it was worth sharing anyway.
Recently, we had a serious fly problem inside the apartment. At night we swatted as many as we could, but during the day the flies were impossible to reach because they would hang out near the skylight over the stairwell. As a result, they were multiplying faster than we could kill them.
We had limited choices to deal with the problem. We didn't want to spray any harmful chemicals or use traps with smelly bait, and our usual response, covering all light sources and leaving one window open, is not an option during the winter.
My solution was to hang a ribbon of fly trap tape below a light source, a desk light for targeted lighting, and to leave the light on overnight. Kind of like an electronic bug zapper, but without the zapping. During the day flies would still hang out near the skylight, but at night, when this was the only light source in the room, they were attracted to the tape like moths to a flame.
Three days with the light trap on and the fly infestation is completely gone. Though, to be safe, we're going to leave it on a few more days to catch any newborns and stragglers.
The only cost involved was the pack of fly trap tape, and since I only used one ribbon, it cost less than a dollar to get rid of all the flies!
If you try this let me how it works for you.