Dipteran flight diversity is shaped by aerodynamic constraints, scaling, and evolutionary trade-offs.

Flight has been a key innovation in insect evolution, yet the selective and mechanistic pressures shaping their flight motor systems remain poorly understood. Here, we present a comprehensive comparative analysis of flight in Diptera (true flies), integrating morphology, wingbeat kinematics, and aerodynamics within a phylogenetic framework. We quantified morphology in 133 species spanning the Dipteran phylogenetic and size range, and for a subset of 46 species, we combined high-speed stereoscopic videography with computational fluid dynamics (CFD) to characterize wingbeat kinematics and aerodynamic performance, respectively. Our results reveal that morphology is strongly structured by phylogeny, whereas wingbeat kinematics are broadly conserved across Diptera, reflecting dominant aerodynamic constraints. Two early-diverged lineages, Culicomorpha (mosquitoes and midges) and Tipulomorpha (crane flies), exhibit strikingly divergent kinematics and aerodynamics, suggesting lineage-specific selective pressures. Combining these data with scaling analyses shows that maintaining in-flight weight support across the dipteran size range requires systematic allometric adjustments in wing morphology, wingbeat kinematics, and flight musculature. Smaller dipterans achieve weight support through relatively larger wings and higher wingbeat frequencies, whereas larger dipterans achieve the same aerodynamic requirement through increased investment in flight musculature to sustain the necessary mechanical power output. These size-dependent trait combinations highlight how different morphological and kinematic adaptations evolved in response to the shared physical requirements of hovering flight across Diptera. Mosquitoes and midges represent an extreme case, exhibiting a pronounced aerodynamic-acoustic trade-off with disproportionately high wingbeat frequencies, large flight musculature and increased aerodynamic and acoustic power, consistent with selection favoring acoustic signaling during in-swarm mating. By integrating comparative morphology, kinematics, and aerodynamics across a major insect radiation, our study uncovers the interplay between physical scaling laws, aerodynamic constraints, and ecological pressures in shaping the evolution of animal flight. These findings provide a mechanistic framework for understanding how complex locomotor systems diversify under multiple selection pressures.