Wing veins Rs and M curved anteriorly:

Wing venation is an important diagnostic characteristic to define a therevid. Therevidae have a relatively primitive wing venation, but we can exclude many closely related families based on their peculiar wing venation characteristics- the first of which is anteriorly directed (towards costal margin) Rs and M veins. This characteristic differentiates Mydidae, Scenopinidae and Apioceridae from Therevidae.

Wing vein M3 absent:

Although not exclusively, the therevid wing has a wing vein M3 present. The absence of such a vein differentiate therevids from most higher flies that lack an antennal arista.

Note: Be careful to ensure that you do not have a Bombyliidae. Bombylidae are easily defined from Therevidae based on genitalic characteristics, and can be differentiated from therevids easily by general body shape. Be aware that Bombyliidae are a large morphologically diverse family and some bombyliid species can be mistaken for therevids by the unwary beginner.