A pair of Anthomyza sp. flies, possibly A. gracilis, mate on a blade of grass. The Anthomyza genus is part of the Anthomyzidae family, whose members are generally less than 3mm in length. The flies in this photo were around 2mm long each.
They tend to occur among grasses and other vegetation bordering ponds or streams, or in marshy areas. (This photo was taken next to a garden pond). The larvae develop between the closely fitting leaf-sheaths of the terminal shoots of the plants.
Images blended for focus in PS CS5