Stealthy moths avoid bats with acoustic camouflage

Intense predation pressure from echolocating bats has led to the evolution of a host of anti-bat defences in nocturnal moths. Some have evolved ears to detect the ultrasonic biosonar of bats, yet there are many moths that are completely deaf. To enhance their survival chances, deaf moths must instead rely on passive defences. Here, we show that furry morphological specializations give moth bodies and wing joints acoustic stealth by reducing their echoes from bat calls. Using acoustic tomography, echo strength was quantified in the spatial and frequency domains of two deaf moth species that are subject to bat predation and two butterfly species that are not. Thoracic fur determines acoustic camouflage of moths but not butterflies. Thoracic fur provides substantial acoustic stealth at all ecologically relevant ultrasonic frequencies, with fur removal increasing a moth’s detection risk by as much as 38%. The thorax fur of moths acts as a lightweight porous sound absorber, facilitating acoustic camouflage and offering a significant survival advantage against bats.

percyhiggenbottom on November 11st, 2018 at 00:01 UTC »

What I take from this is that someone's job was to shave moths for a time.

Compy222 on November 10th, 2018 at 20:23 UTC »

Fascinating. Evolutionary stealth absorbent coatings, that's some cool stuff.

stereomatch on November 10th, 2018 at 18:31 UTC »

News coverage:

Moths use acoustic camouflaging fur to evade bats

Scientists in the UK have discovered that the fur of some moths can absorb up to 85% of incoming ultrasound. According to the researchers, this fur acts as a “stealth coating” providing the moths with a passive, acoustic camouflage that helps hide them from the ultrasonic clicks of insect-hunting bats. The team says that the fur could inspire the development of biomimetic materials for ultrathin sound absorbers and other noise-control devices.

Bats love to eat moths, which they hunt down using a biological sonar technique, known as echolocation. In the arms race between predator and prey, some moths have evolved ears so they can hear the ultrasonic calls of bats and take evasive action. But it turns out that others have evolved a more passive defence in the form of acoustic camouflage.

At bat echolocation frequencies, the team found that the thorax fur of the moths acted as an acoustic camouflage, absorbing up to 85% of the incoming ultrasound. In contrast, most butterflies absorbed just 20% of incoming ultrasound.

“We tested the absorption from 20-160 kHz, this covers the frequencies that most bats use to hunt their prey, with most calling from 20-60 kHz, whilst there are a few that go to higher frequencies,” Neil explains. “We found the absorption to be remarkably consistent across the range tested, with no apparent frequency dependence in the effect on absorption.”

Paper:

The micromechanics and bioacoustic behaviour of Bunaea alcinoe moth scales

Stealthy moths avoid bats with acoustic camouflage