Our house is two years old, and for the last two summers we have had a serious house fly problem. The flies are getting in via the fans in the upstairs bathrooms. We have spoken to the builder about this and he says there is nothing that can be done, other than keeping the fan going all the time. We mentioned about putting in a screen, similar to the ones on windows, on the outside to prevent them from coming in but the builders says this could burn out the fan. Do you have any ideas to prevent house flies from coming in?
Answer:
I don't think you're dealing with house flies - I think they're cluster flies. They look the same and are the same size but when a house fly lands, the wings are spread out while the cluster fly's wings overlap when in the non-flight position. There really isn't a whole lot to be done about them but your screen idea, particularly from August to freeze-up should still work. Make the screen a large one and monitor it so you don't find it all blocked and then, as your builder suggests, burn out the fan motor.
