Mosquitoes in the US used to be mostly Aedes, but now there are a lot of Culex, which fly twice as fast (120cm/s, or about 2.7 mph) and are better hunters. The Aedes come into a room, find a wall, and eventually eat, while Culex go straight for the bite. Both of them tend to fly upwind toward meals. I wonder whether fans blow the close mosquitoes away but draw lots more to the area, in search of that good human-food smell the fan disperses.