Comparative functional morphology of the wings of Diptera

Wings of representative species of the order Diptera were compared with a simple model structure in which corrugated spars diverge from a V-shaped leading edge spar. Both develop torsion and camber when subjected to aerodynamic loads, forming a propeller shape. Both the leading edge and the cubitus of flies' wings twist basally, allowing camber to be set up as the media hinges up or down at the arculus. Three different wing types were identified: stiff wings possessing two or three main spars; and wings capable of ventral flexion. In wings possessing only two spars, found mainly in the Nematocera, control of camber is achieved largely by the use of cross veins. Wing control and flight are generally imprecise. The third spar, found in most Brachycera, in the Syrphidae and in the Conopidae controls camber and helps support a broader wing. Finer control of camber is exerted by marginal cross veins, and these insects generally have precise, darting flight. Ventral flexion mechanisms are found in the Simuliidae, the Stratiomyiidae, and widely in the Schizophora. Control of ventral flexion, which occurs at the end of the downstroke, allows fast, unpredictable manoeuvres. Functional similarities indicate either phylogenetic relationship or convergence.