Haemodynamic mechanism of dissipation of muscular energy in hovering hawkmoths (Sphingidae).

The dynamics of blood flow and fuel delivery to the flight muscles of hovering hawkmoths are critical for evaluating energy budgets of these energy-demanding organs. The classic wing-flapping scenario ignores the blood contribution to muscle-wing coupling by modelling wing actuation as an elastic spring-muscle actuator pair. We show that a damper controlled by haemodynamics is required. Using data on blood viscosity in resting hawkmoths and analysing flight-muscle structure from X-ray tomography, we developed rheological and fluid-flow models of blood flow through the flight muscles of hovering hawkmoths. These models specify the damper characteristics, revealing the role of packing density of muscle fascicles, wingbeat frequency and fuel source on the drag forces exerted by flowing blood on contracting muscles.