We have been having an awful mosquito issue and I can't figure out where the little beasts are coming from. We live in Michigan and it's winter so am pretty confident in saying they are breeding somewhere in the house, but where? we don't have any standing water and I thought all types needed that to reproduce. I'm killing at least four a day and they are large.
Hmm, I was really hoping they were crane flies... I was seeing mosquitoes all year, last winter here in PA. It's just awful with this new invasive species (the asian tiger mosquito which is an all day mosquito and doesn't hum like the ones when I was a kid which were only out at dawn and dusk). Maybe they are breeding in any potted house plants that you have? They only need a tiny amount of water. They'll lay their eggs in a knot of wood and when it fills up from rain, the eggs will hatch out. Mosquitoes eat leaves and the females just need blood to lay eggs. So no leaves, no food.
Do you have any houseplants? My oldest has a bamboo plant, and we've found mosquito larvae in the water before...
Maybe you could temporarily put all your houseplants in a separate room with a closed door? They need the plants for food so, at least, you'd be removing their food source if they aren't breeding in the pots.