The asynchronous flapping oscillator in blue bottle flies: mapping the parameter space through application of weight to wings

Insects of the higher Neoptera flap their wings by an asynchronous mechanism: Wing strokes are not individually triggered by nerve impulses; rather, delayed stretch-activation allows the flight muscle to oscillate spontaneously when coupled to a resonant load. This type of ‘distributed’ control mechanism has obvious advantages such as neurological economy and robustness against perturbation, but the implications have not been fully explored. Previous researchers have found only that asynchronous flappers are constrained to a narrow frequency range. We have constructed mathematical and mechanical models of delayed feedback oscillators that display additional complex dynamics which have not been observed in insects. I used audio and high-speed video recordings of blue bottle flies to investigate the further consequences of asynchronous flight control. By mapping the dynamical parameter space displayed by a real insect, I concluded that the delayed feedback oscillator mechanism is indeed sufficient, despite my data suggesting that there is no simple harmonic motion and that no elastic forces act in the wing system of the flies. However, I believe this counterintuitive data is caused by brief periods of anharmonicity at the upper and lower extrema due to the elastic components’ increased stiffness, resulting in an overall higher frequency, and not because the flies abandon the mechanical oscillator scheme altogether.