School of Biological Sciences, University of Bristol, Bristol, UK.
Department of Mechanical Engineering, University of Bristol, Bristol, UK.
J R Soc Interface. 2020 Feb;17(163):20190692. doi: 10.1098/rsif.2019.0692. Epub 2020 Feb 26.
Many moths are endowed with ultrasound-sensitive ears that serve the detection and evasion of echolocating bats. Moths lacking such ears could still gain protection from bat biosonar by using stealth acoustic camouflage, absorbing sound waves rather than reflecting them back as echoes. The thorax of a moth is bulky and hence acoustically highly reflective. This renders it an obvious target for any bat. Much of the thorax of moths is covered in hair-like scales, the layout of which is remarkably similar in structure and arrangement to natural fibrous materials commonly used in sound insulation. Despite this structural similarity, the effect of thorax scales on moth echoes has never been characterized. Here, we test whether and how moth thorax scales function as an acoustic absorber. From tomographic echo images, we find that the thin layer of thoracic scales of diurnal butterflies affects the strength of ultrasound echoes from the thorax very little, while the thorax scales of earless moths absorbs an average of 67 ± 9% of impinging ultrasonic sound energy. We show that the thorax scales of moths provide acoustic camouflage by acting as broadband (20-160 kHz) stealth coating. Modelling results suggest the scales are acting as a porous sound absorber; however, the thorax scales of moths achieve a considerably higher absorption than technical fibrous porous absorbers with the same structural parameters. Such scales, despite being thin and lightweight, constitute a broadband, multidirectional and efficient ultrasound absorber that reduces the moths' detectability to hunting bats and gives them a survival advantage.
许多飞蛾具有对超声波敏感的耳朵，用于探测和躲避回声定位蝙蝠。没有这种耳朵的飞蛾仍然可以通过使用隐形声学伪装来保护自己免受蝙蝠生物声纳的影响，即吸收声波而不是将其反射回回声。飞蛾的胸部体积庞大，因此在声学上具有很强的反射性。这使它成为任何蝙蝠的明显目标。飞蛾的胸部大部分都覆盖着毛发状的鳞片，其结构和排列与隔音中常用的天然纤维材料非常相似。尽管结构相似，但胸部鳞片对飞蛾回声的影响从未被描述过。在这里，我们测试了飞蛾胸部鳞片是否以及如何作为吸声体发挥作用。从断层回声图像中，我们发现日间蝴蝶的薄胸部鳞片层对胸部超声回波的强度几乎没有影响，而无耳飞蛾的胸部鳞片则吸收了平均 67±9%的入射超声声能。我们表明，飞蛾的胸部鳞片通过充当宽带（20-160 kHz）隐形涂层来提供声学伪装。建模结果表明鳞片起到了多孔吸声体的作用；然而，飞蛾的胸部鳞片比具有相同结构参数的技术纤维多孔吸声器能实现更高的吸收率。这些鳞片虽然很薄很轻，但构成了宽带、多方向和高效的超声波吸收体，降低了飞蛾对捕猎蝙蝠的可探测性，使它们具有生存优势。
