Hearing like a fly: A 3-dimensional directional microphone inspired by O. ochracea*

The parasitoid fly Ormia ochracea famously locates both its prey and predators by sound to an accuracy 2° in the horizontal plane despite having an hearing organ spacing of only 500 μm, via mechanical coupling. The existing one dimensional mechano-mathematical model for O. ochracea’s hearing response accurately predicts the interaural amplitude difference (IAD) between the tympana at all azimuthal incident sound angles but cannot correctly predict the interaural time difference (ITD) at high azimuthal angles. Recent synchrotron radiation microtomography (SR-μCT) revealed more information about the 3D morphology of O. ochracea tympana. In contrast to previous assumptions of near two-dimensionality, these results displayed a complex, highly three-dimensional structure. Inspired by our observations of the 3D morphology of O. ochracea tympana, we created a finite-element analysis model to develop a novel microphone design that integrates acoustic sensing in multiple planes. Through this updated design, we increased the amplitude of response at high incident sound angles compared to existing planar designs, leading to a new ormia-inspired device with improved directional sensing capabilities.