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A particularly fluffy moth species (Periphoba arcaei) displaying highly elongated thorax scales which act as a type of acoustic camouflage against bats.

Deaf moths use ‘noise-cancelling scales’ to evade bat capture

Image credit: Thomas R. Neil

Some species of deaf moths can absorb as much as 85 per cent of the incoming sound energy from predatory bats, who use echolocation to detect them, according to researchers from the University of Bristol.

The team’s findings, published in the Journal of the Royal Society Interface, reveal that these types of aurally challenged moths, who are unable to hear the ultrasonic calls of bats, have evolved this clever defensive strategy to ensure their survival.

Bats hunt for their food at night using echolocation. This technique, which is also known as biological sonar, first evolved around 65 million years ago and enables bats to search for and find prey, putting huge predation pressure on nocturnal insects.

One defence mechanism that many nocturnal insects evolved to avoid becoming prey is the ability to hear the ultrasonic calls of bats, allowing them to actively evade approaching bats.

Many moth species, however, cannot hear. The researchers were intrigued to investigate the alternative defences against bats that some species of deaf moths might have evolved.

One of the four species used in the present study (Antherina suraka). The thorax scales on this moth can absorb up to 85% of the sound energy produced by an echolocating bat.

One of the four species used in the present study (Antherina suraka). The thorax scales on this moth can absorb up to 85 per cent of the sound energy produced by an echolocating bat.

Image credit: Thomas R. Neil

Using scanning electron microscopy (a scanning electron microscope produces images of a sample by scanning the surface of an object or living being with a focused beam of electrons), the team discovered that the thorax scales of the moths ‘Antherina suraka’ (pictured above) and ‘Callosamia promethea’ looked structurally similar to fibres that are used as noise insulation.

With this knowledge about the moths’ characteristics, the team explored whether the thorax scales of moths might be acting in some way to absorb the ultrasonic clicks of bats and dampen the echoes returning to the bat, offering the moths a type of acoustic camouflage.

The team measured that the scales on the body of a moth absorb as much as 85 per cent of the incoming sound energy and that these scales can reduce the distance at which a bat would be able to detect a moth by almost 25 per cent, potentially offering the moth a significant increase in its survival chances.

A composite image of a moth and a butterfly showing how we can use acoustic tomography to create a picture using sound. The colour images show the target species whilst the grey scale is the resultant tomographic image. This technique allows the team to measure exactly how much sound is being reflected from certain body parts of a specimen.

A composite image of a moth and a butterfly showing how we can use acoustic tomography to create a picture using sound. The colour images show the target species whilst the grey scale is the resultant tomographic image. This technique allows the team to measure exactly how much sound is being reflected from certain body parts of a specimen.

Image credit: Thomas R.Neil and Marc W Holderied

“We were amazed to see that these extraordinary insects were able to achieve the same levels of sound absorption as commercially available technical sound absorbers, whilst at the same time being much thinner and lighter,” said Dr Thomas Neil, a research associate from the University of Bristol’s School of Biological Sciences.

“We are now looking at ways in which we can use these biological systems to inspire new solutions to sound-insulating technology and analyse the scaling on a moth’s wing to explore whether they too have sound-absorbing properties,” he added.

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