Bio-inspired urban adaptations: what insects can teach us about dealing with noise

Professor Marc Holderied has devoted more than 20 years of his life’s work to understanding how bats have evolved and what their extraordinary abilities can teach us about adapting to our ever-changing environment. Building on this rich foundation as a sensory ecologist and bio-acoustician, he is gathering a team of fellow researchers and commercialisation experts who can help to take his work on bio-inspired sound absorbers to the next level.

This Enterprise Fellowship project has the potential to bring significant benefits by solving the social, health and environmental problems of urban noise pollution. Not only that, it’s one that Professor Holderied believes provides yet more evidence for the attention, respect, care and wonder that nature deserves.

You’re renowned for your work on wildlife acoustics and acoustic camouflage. When did you first become interested in this, and why does it continue to inspire you?  

I always wanted to be a scientist, even before I could pronounce the word! For my ninth birthday, my aunt gave me a nature guidebook that I took everywhere, identifying everything I could find. My passion for bats started when I was around 17 when I went on a winter bat count. At university, there was a professor whose specialism was bioacoustics, in particular bats, and it was just the perfect match – from then on, it was all about sound.

Bats are the most fascinating mammals, for the simple reason that they do two things that no other mammal does: they can do active flight and they can echolocate. As a result, there are so many more constraints on the standard mammalian design that they have had to implement, with amazing special adaptations.

Then there is this whole hidden world available to them because they see with their ears. I find it fascinating that bats have control over what information they receive. That adaptive sensing is an intriguing implementation of physics into biological behaviour, which can be linked to the physics of sound manipulation – there is so much that has gone into this that can inspire bioinspired engineers for a long time.

Of all the investigations you’ve been involved in and the discoveries you’ve made, what do you consider to be the most striking?

What has really kept me busy for the last decade is the evolution of echolocation and examples of convergent evolution. There are organisms out there that want to manipulate how their echoes sound to a bat to suit their own ends – in the same way that a flower manipulates our visual perception by producing colour, there are plants out there that want to be found by bats as they are pollinators. We have studied the echo-acoustic equivalent of colour in these bat-pollinated flowers. Now we mainly work with organisms that don’t want to be found by echolocation – prey insects.

There are nocturnal insects out there that have no ears to detect bat calls – they have to depend completely on passive defences. The ones with ears obviously have an advantage, and theoretically, insects without ears should be easy prey.

This led us to look at moths, specifically silk moths, which have no other defences and completely depend on their very furry bodies. We found that when their furry exterior was removed, their echoes became much louder, suggesting that the fluff on their bodies absorbs sound and prevents their detection by bats. But how can they equally reduce echoes from their wings without compromising their energetics or aerodynamics? The body fluff would be too thick. We discovered they have evolved a very thin structure of overlapping scales that dampens the sound they reflect back to bats at a rate that is about ten times better than any sound absorbers humans use, for noise control for instance.

Moths have effectively evolved an acoustic metamaterial with emergent properties. We now understand enough of this mechanism that we can replicate it with the aim to make our world a less noisy place.

Your Enterprise Fellowship is focused on exploring the commercial potential for this bio-inspired noise control solution. What do you hope to achieve?

Noise is the second-biggest environmental health risk for humans, particularly in urban Western environments. In Europe alone we lose over a million years of healthy life through noise every year. The UK government estimates that the negative health losses – including cardiovascular disease and blood pressure – and the societal costs of road noise alone are higher than the cost for all the road traffic accidents (that’s in England alone), causing an annual bill of over £9 billion.

The promise of the moth wing is that we can create a sound absorber that can provide a level of absorption at a fraction of the space requirements, and hopefully produce a product that people can put in their living rooms to improve their living conditions.

That’s our mission – to make the world a quieter and healthier place.

Did you always have a commercial output in mind when you began working on this?

Personally, I’m a curiosity-driven researcher – I want to know ‘how’. My primary motivation isn’t that I want to be an entrepreneur, I’m perfectly happy discovering things. But I also don’t want to be the person who has lots of regrets from not even attempting something new.

I stumbled upon this nugget of gold, and the Enterprise Fellowship came at a perfect time, when I was looking at commercialisation ideas. As a professor with a very dense teaching load, the prospect of having to do a full CEO role on top of my full academic role is impossible. The Enterprise Fellowship scheme is fantastic because it gives buyout to my department and will be run like a sabbatical, which allows me to reduce my teaching load and invest a substantial amount of time into enterprise activities.

Your work in reverse engineering seems a potent example of how invaluable nature is in teaching us how to survive and thrive through adaptation. What other lessons do you think we can learn from this?

I’m a very engineering-inspired biologist, but I’m a naturalist too, so I’m saddened by the loss of insect biodiversity. Everything that is diminished means fewer things for us to study and discover, so this loss of wildlife is an immense problem for ecosystem stability. From an ecological standpoint, we need to have a readiness to defend every organism that lives and shares our habitat with us. But from a very selfish standpoint, if we lose them, we lose all the ingenious inventions that they carry with them, without us even noticing.

There is great awareness about the importance of nature in terms of proteins, genetics, chemical defences and antibiotics. Here, we have found an example of how sensory ecology can help make our lives and our environment much healthier and better in general.

Everything in the ecosystem has a role to play, is a brick in the building, and if you lose one after the other, the whole thing eventually collapses. Moths are beautiful creatures and beneficial in many ways; my hope is that more people will realise that.

Marc Holderied is Professor of Sensory Biology in the School of Biological Sciences. He is also a member of the Cabot Institute for the Environment, and Bristol Neuroscience.