Influence of spider hair structure on acoustic response

It is well known that spiders have an extraordinary auditory sensitivity. However, significant differences in the acoustic impedance between air and solids (spiders) would reduce the acoustic energy transmitted from air to spiders, and by intuition this might result in a significant decrease in the acoustic sensitivity of spiders. This mechanism has been long troubled in researchers’ minds that how hunting spiders could have an outstanding auditory sensitivity. In this paper, the auditory sensing mechanisms of hunting spiders are studied by theoretical analysis and simulation. The results show that the acoustic impedance can be adjusted by spiders’ hairs with particular features to realize the acoustic impedance matching between air and spiders, which could make spiders’ hairs easily send signals to the nervous system of spiders, thus significantly promoting the acoustic energy transfer from air to spiders. Both the appropriate length and deflection angle of hairs are critical to determine the acoustic impedance/acoustic transmission coefficient. In parallel, verification test is carried out on an innovative bionic hair array. The experiment result shows that the acoustic impedance is significantly descended by the bionic hair array with the spiders' acoustic hairs' features, which provides a sufficient proof of the acoustic impedance matching by spiders' hairs. Consequently, this work clearly discloses the acoustic sensing mechanism for the extraordinary auditory sensitivity of hunting spiders, which may have a great significance for the development of artificial auditory technology and sound stealth devices.