The Society for the study of flies (Diptera)

I am working on a dietry study of swallows using faecal analysis. I can recognise Stratiomyidae(often Beris sp) by wings and scutellum, but often associated with this is a head in which the eye facets are of different sizes - larger anteriorally than posteriorally. Does anyone know if this is the Stratiomyid mentioned? I also find Simulium sp. The antennae of both these sp are very similar. Does Simulium have eye facets of different sizes?