The junction of the radial and cubital wing veins, which is usually swollen. The presence or absence of setae on the node is an important identification character in, for example, Muscidae.
Anyone has "Chironomidae of the Holarctic region. Keys and diagnoses. Part 3. Adult Males Entomologica Scandinavica Supplement 34"?
smolwaarneming@gma il.com
Does someone has a scan of Nartshuk E.P. 2003. Key to families of Diptera (Insecta) of the fauna of Russian and adjacent countries. Proceedings of the Zoological Institute Vol. 294: 1-252 for me?