Cluster Flies in my office

So a few years ago we pressure washed the building I work in. This caused all the dust, dirt, and grime that was holding the paint on. later that fall we became infested with cluster flies. As you can see above they are ugly, and large (not as big as the picture). One positive is they are slow, I can kill them with my hand (with has caused me to wash them every 2 minutes). Though it is getting a little old. Until tomorrow when the pest man shows up.