Where are these flies coming from?

Question

I turned off the AC and opened the windows (all with screens that are in tact) and so far we have killed or put out at least a dozen and a half of these flies that are about double the size of a "normal" house fly. They seem to like to dive bomb us. What are they and where are they coming from?

Answer 1

http://www.colostate.edu/Depts/CoopExt/4...

Answer 2

I haven't found what they're called, but yeah, they seem to be much bigger than your typical house fly.  This happened to me once and freaked me out because I hadn't left doors or windows open and yet the apartment was swarmed with them.  Turned out, I had forgotten a small bag of garbage in a corner of the kitchen.  Gross, lol.

A guy in another Y!A provided this link

http://www.fliesbegone.com/