Insects select flight speeds that coincide with low metabolic energy expenditure

Abstract Aerodynamic theory predicts a U-shaped relationship between mechanical power and airspeed. Empirical data from birds and bats support a similar U-shaped metabolic power–speed curve, reflecting the underlying muscle mechanics. However, data on insects’ flight energetics remain limited and sometimes conflicting, with some studies reporting airspeed-independent metabolic rates and others suggesting U-shaped relationships. To evaluate whether a consistent metabolic power–speed relationship exists across insect orders, we quantified the energetic cost of tethered flight across a range of airspeeds (0–4 m s–1) in four species—bumblebee (Bombus terrestris), desert locust (Schistocerca gregaria), blowfly (Calliphora vicina) and privet hawkmoth (Sphinx ligustri). Clear curvilinear relationships between mass-specific metabolic power and airspeed were observed across all species: U-shaped in Bombus and Schistocerca; and skewed U-shaped in Calliphora and Sphinx. The speed corresponding to the minimum mass-specific metabolic cost of transport coincided with reported preferred flight speed ranges in all species. This suggests that these species are physiologically attuned to fly at speeds that minimize flight energetics and economy. Despite substantial differences in phylogeny, wing morphology and muscle physiology, these findings provide experimental evidence for airspeed-dependent metabolic power curves in insects and highlight the importance of flight energetics in speed selection.