This is the first of three pictures from a swarm (different individuals). They kept landing on me and then chasing each other (mating behavior? territoriality?) and were uninterested in my lunch or my skin (though it was dry and I was sweating quite a bit). Wing veination was similar to that of a housefly as seen at the U. Nebraska website (http://entomology.unl.edu/images/muscidflies/housefly.jpg ), but these seemed bigger and hairier than the houseflies around my house. A tachinid of some sort?