Bats eat a lot of moths, which they locate in the dark via echolocation. According to new research, however, some moths have evolved sound-absorbing fur as a passive means of defence – and it could inspire advances in human technology.

Although many moth species are deaf, some have evolved ears that allow them to evade bats by hearing the animals' ultrasonic calls. When the University of Bristol's Dr. Thomas Neil examined moths that didn't have those ears and thus remained deaf, he discovered that their thorax and wing joints were covered with an "acoustic stealth" fur that might keep the calls from echoing back to the bats.

In lab tests that measured objects' echo strength, it was found that the thorax fur of two species of deaf moth absorbed up to 85 percent of incoming sound energy. By contrast, when Neil tested two species of butterfly that are not preyed upon by bats, their less-dense fur absorbed no more than 20 percent. Additionally, when the thorax fur was removed from the moths, their detection risk increased by as much as 38 percent.

"Thoracic fur provides substantial acoustic stealth at all ecologically relevant ultrasonic frequencies," says Neil. "The thorax fur of moths acts as a lightweight porous sound absorber, facilitating acoustic camouflage and offering a significant survival advantage against bats."

He now believes that the acoustic qualities of the fur could be applied to technology such as ultrathin sound-absorbing materials, as the fur's performance is reportedly on par with that of presently-used sound-absorbing foams.

Neil is presenting his research this week at the Acoustical Society of America's 176th Meeting in Victoria, Canada.