Mesothoracic flight organ (ex McAlpine 1981).
The wing venation in the Milichiidae consists of the costa (C), rudimentary subcosta (Sc), radius (R1, R2+3, and R4+5), media (M1), anterior cubitus (CuA1 and CuA2), and anal vein (A1). Anteriorly at the base of the wing there is the humeral crossvein (h); between R4+5 and M1 there is the radial-medial crossvein (r-m), and between M1 and CuA1 there is the basal medial-cubital crossvein (bm-cu) as well as the discal medial-cubital crossvein (dm-cu). At the base of the anal vein there are the posterior cubital cell (cell cup, 'anal cell') and the anal lobe. The distal margin of the posterior cubital cell is formed by CuA2.
In the stem-species pattern of the the Chloropidae family-group, the shape of the wing is oval. However, in the Milichiidae, in stem-species H (Milichiinae without Enigmilichia), the anal lobe is apomorphically well developed and the apex of the wing is narrow, in males more so than in females. This gives the wing a more triangular shape. The condition in Enigmilichia is intermediate. In Xenophyllomyza the anal lobe is also convergently well developed, but the apex of the wing is not narrower than in the stem-species pattern of the Milichiidae.
According to J. F. McAlpine & Munroe (1968) a large anal lobe and a triangular wing indicate species that swarm and complete the initial stages of mating in flight. A large anal lobe and narrow wing apex is thought to improve the insects ability to hover and manoeuvre with the precision required for successful aerial coupling. The shape of the wings of Milichiinae correspond to this hypothesis, since swarming is known for several species (ex Brake 2000).
In the Diptera only the front or mesothoracic pair of wings is developed as functional flight organs; the metathoracic pair is reduced to small club-like structures, the halteres. This feature is an outstanding apomorphic character of the order (ex McAlpine 1981).