I don't know why the houseflies are bothering me so much more than the other two. Maybe it's that they're bigger. Maybe I've just forgotten how much the other two bothered me. Maybe it's that it is highly nonobvious where the heck the houseflies are coming from. Maybe it's that I went to a lot of effort to kill almost all the ones I could find yesterday (there were dozens, and they almost exclusively hung out in the kitchen), and I come home today after work and there are dozens again, like goddamn deja vu.
Houseflies are attracted to light, so one thing that works is to take a clamp light and point it at a strip of flypaper that is placed up against a wall (to reduce the mean free path in the lit volume). You're welcome. (A variant, if the fly-infested area is close to an exterior door, is to take a flashlight and Pied-Piper them out.)
Oh and also I'm sick again. COMPLAIN.