Aulacigastridae
Aulacigastridae is a very small family of flies known as sap flies. The family Stenomicridae used to be included within this family, but was moved by Papp in 1984. They are found in all the Ecoregions. Description. For terms see Morphology of Diptera. Aulacigastrids are small black flies. The head is rounded. Postvertical bristles and ocellar bristles are absent, there are two orbital bristles on each side of frons, the anterior orbital bristle directed forward and towards median line. Vibrissae are well developed. On the mesonotum there are two pairs of dorsocentral bristles. The costa is interrupted near the  subcosta (which reaches the costa). The posterior basal wing cell and discoidal wing cell are fused and the anal vein does not reach the margin of the wings. Biology. The larvae of sap flies feed on the sap of deciduous and coniferous trees (sap runs) and feed on micro-organisms within the sap. Adults feed on nectar, and other fermenting substances.