A 3D rendering of the acoustic camouflage pattern of a moth wing
Simon Reichel, Thomas Neil, Zhiyuan Shen and Marc Holderied
Earless moths have sound-absorbing wings that act as acoustic camouflage for prey bats. The moth wings have an ultra-thin cuticle that absorbs sound and could be adjusted for noise-canceling technology.
Marc Holderied of the University of Bristol, UK, and colleagues projected sound waves onto the wings of two species of earless moths (Antheraea pernyi and Dactyloceras lucina). They found that the sound waves bouncing back from the moth’s wings were much quieter.
Using an imaging technique called acoustic topography, the team found that these moth wings have a layer of scales arranged in a special repeating pattern that absorbs sound over a wide range of frequencies.
“Similar to the way stealth bombers can be less perceived by enemy radars, the moths have developed a stealth coating against the bat’s sonar,” says Holderied. The moth’s wings, which are about a tenth of a millimeter thick, absorb the specific sound waves generated by bats.
Bats interpret their environment through echo localization: they send out sound waves, and when the sound hits an object, an echo is created. The bats use these echoes to create a picture of their surroundings. Because the ears of the earless moths absorb these sound waves, they remain largely undetected and improve their chances of survival.
Other moths have ultra-sensitive ears to hear bats, but the deaf, earless moths rely on this sound-absorbing layer to evade their predators.
Holderied and his team also compared the earless moths with two types of butterflies and found that only the moths had the sound-absorbing quality.
Although these wings only absorb sound that bats hear, it could be adapted for human sound frequencies, says Akito Kawahara of the Florida Museum of Natural History. This could prove useful in applications such as mufflers and noise canceling headphones.
Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073 / pnas.2014531117
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