Springs and Wings: Elastic Energy Exchange in Insect Flight

In many insects, wing movements are generated indirectly via deformations of an exoskeletal shell. Estimates of power expenditure suggest that elastic energy recovery between wingstrokes may reduce flight power requirements. We tested three questions: 1) Can the thoracic shell provide significant energy return? 2) Does a simple damped elastic model describe bulk mechanical behavior? and 3) Are different thorax regions specialized for elastic energy exchange? We measured deformation mechanics by recording the force required to sinusoidally deform the exoskeleton over a wide frequency range. Elastic energy storage in the exoskeleton is sufficient to minimize power requirements and a structural (frequency-independent) damping model, not a viscoelastic one, describes bulk mechanical properties. We next performed complementary experiments on a structurally damped hemispherical shell. In contrast to the hemispherical shell, mechanical coupling between exoskeleton regions improved spring performance and local properties depended on global strain patterns. We found regions specialized for energy recovery with low dissipation, highlighting the specificity of exoskeleton regions for flight energetics. Finally, we consider the implications of resonance mechanics on flapping wing flight.