It was in the past 5 years or so… there were tons of flies, there were people like in a Western ghost town or something. There may have been something possessed or contagious about the flies. It looked scary as hell but I never caught the name. Any takers?
Legion?
The first part of Legion’s trailer had me thinking you found it, but then it turned all fantasy/action which wasn’t what I remembered. (Of course my memory has been known to be patchy).
The trailer I remembered seemed to be all about the flies, like these people are passing through a small town and all the flies are seriously bad news in some way.
I’m thinking maybe The Reaping starring Hilary Swank ?
How about Reeker ?