Sound advice from a deaf moth
Morning birdsong and children giggling are often sounds we all love to hear. Not so delightful sounds include ongoing construction noise and a neighbour’s loud television set. This is when thoughts of installing soundproofing might come up. Now the best sound-proofer in town has flown in and it seems that we have a lot of science to learn from a tiny furry moth that can’t even hear sounds itself.
Sound is a series of molecule vibrations that we usually hear as they travel through the air. If the vibrations make it inside our ears with enough energy to stimulate the tiny hairs in there, our brains register it as noise. The larger the energy the louder the sound.
To try to reduce the volume of sounds, rubbery and fibrous materials that readily absorb these travelling sound waves are typically used to try and soak up some of the energy from the vibrations so less of them get to our ears. These materials are typically hung or laid as wall, floor and ceiling coverings.
The more sound that is needed to be absorbed the larger and heavier the soundproofing needs to be.
Research published in the journal Royal Society Interface this week might change all of this thanks to new discoveries about a tiny little deaf moth and its lightweight soundproofing solution.
If you are a nocturnal insect like a moth, one of your predators will be bats. As it’s hard to see your lunch in the darkness of the night, bats have evolved to hunt using
Dr Michelle Dickinson, creator of Nanogirl, is a nanotechnologist who is passionate about getting Kiwis hooked on science and engineering. Tweet her your science questions @medickinson
echolocation.
By emitting a high-pitched sound, bats can detect where that sound bounces off a solid object such as an insect. They can then use this returning sound to “see” their prey using sound waves and their ears rather than seeing them using their eyes and light waves.
To try to beat the bat system, many nocturnal insects, including moth species, evolved so that they could hear the ultrasonic calls of the bats and dodge them during a chase. Sadly some moth species are totally deaf and so don’t know when a hungry bat is close.
Rather than just remain susceptible to being eaten, some of these deaf moths have evolved a “noise-cancelling” coating on their bodies which researchers have just found to be more efficient than any soundproofing solution made by humans.
In the study, scanning electron microscopes were used on two species of deaf moths, the Antherina suraka and Callosamia promethean, where unique scales coated in tiny hairs were discovered.
The researchers tested the sound absorption properties of these scales using a technique called acoustic tomography.
Here, ultrasound pulses were played through a loudspeaker and the strength of the echoes that bounced back were measured.
Incredibly they found that the moth scales were able to absorb 85 per cent of the incoming sound energy.
Though this is the same level of sound absorption as highly technical large manmade sound absorbers, the moth scales won by being much thinner and lighter than anything humans have made.
The findings were good news for the moth as this level of sound absorption means their hairy scales were able to act as a sound camouflage protecting the moth from being detected from a distance and therefore increasing their chances of survival.
Though no moth cloth has been made yet out of this newly discovered furry fabric, it could help manufacturers make better, lighter soundproofing material. It also shows — yet again — that Mother Nature is way ahead of us, having already developed a solution we humans are still working on.