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This morning I compared the photo to some (rather old) specimens of Madiza glabra, and it matched very well. Among the features which seem characteristic - the sphaerocerid-like head shape with flat frons, the chunky legs, the milky wings, the long bristles at the end of the abdomen, and the shining black haltere. This last feature (visible in front of and slightly below the white flash spot at the base of the abdomen) is rarely found - the halteres of most flies are white, yellow or brown.
But exactly which species of Madiza this is ...? I suspect we may need the specimen.