Want to read more?
At the start of the pandemic in March we took the decision to make online access to our news free of charge by taking down our paywall. At a time where accurate information about Covid-19 was vital to our community, this was the right decision – even though it meant a drop in our income.
In order to help safeguard the future of our journalism, the time has now come to reinstate our paywall, However, rest assured that access to all Covid related news will still remain free.
To access all other news will require a subscription, as it did pre-pandemic. The good news is that for the whole of December we will be running a special discounted offer to get 3 months access for the price of one month. Thanks you for supporting us during this incredibly challenging time
We value our content, so access to our full site is only available on subscription.
Your subscription entitles you to 7-day-a-week access to our website, plus a full digital copy of that week’s paper to read on your pc/mac or mobile device.
And there’s more – your subscription includes access to digital archive copies from 2006 onwards.
Have you ever wondered why moths have hairy bodies while butterflies don’t?
Scientists at Bristol University have recently researched this question and come up with an intriguing answer (*).
The bodies and wings of both butterflies and moths are covered in scales, but on a moth’s thorax these scales are elongated to resemble hairs. Why? Because this modification very effectively protects moths from becoming bat-fodder.
Butterflies are active during the day but moths are mostly nocturnal. And under the night sky moths make a tasty meal for insectivorous bats. These tiny mammals detect their prey by echo-location, a method of hunting that involves emitting repeated ultrasonic squeaks, generally with a dominant frequency range of 20-60 kilohertz (kHz). Their prey is then located from the direction of the returning echoes.
Moths have evolved various mechanisms to evade these predators: some have developed ears that detect bat echolocation calls, allowing them to take evasive action, but others, the earless moths, have to rely on passive defences – so-called acoustic camouflage – that is, their hairy thoraces.
Comparing tomographic echo images from two species of earless moths with two species of diurnal butterflies, the Bristol scientists found very little effect on the ultrasound echoes from the thin layer of thoracic scales of butterflies. In contrast, the hair-like scales covering moth thoraces absorbed around 67 per cent of the ultrasonic sound energy in the broadband 20-160 kHz. This provides clear protection from hunting bats and consequently is a very significant survival advantage.
Addressing the mechanisms behind the ultrasound reduction achieved by moth thoraces, the scientists found that the hair-like scales form a connected network of air pockets, which act as porous ultrasound absorbers. Sound waves entering the network cause air molecules in the pockets to vibrate, thereby dissipating energy and reducing echo reflection.
The overall arrangement and microstructure of hair-like moth scales closely resembles man-made fibrous materials designed to absorb sound but, interestingly, the Bristol team showed that the moth scales have a considerably higher absorption capacity. So perhaps we could learn lessons from these small hairy creatures.
* J. R. Soc. Interface 17: 20190692 (2020).