I think I had one lay eggs in my house. A few weeks ago, on a day when I hardly opened a door for more than a few seconds I suddenly found at least 100 horseflies in my house. I was sucking them up with a hand vac and releasing them outside, and every few hours I’d go suck up about 30 more — and every single day after that I found at least 30 or so more for at least a week. I’m still seeing 1-2 per day, but at least that’s manageable. Hopefully these last stragglers are the last that I’ll have. It’s nuts!