The greater wax moth can hear at a higher frequency than any other animal on Earth, according to a new study.
These insects, whose ears are each only about the size of a pinhead, can recognize sounds between 30 and 300 kilohertz (kHz)—a range never before seen in the animal kingdom.
People speak at about 3 kHz. In youth we can hear up to about 20 kHz, but we lose our ability to recognize higher frequencies as we age. Dogs generally hear frequencies of about 30 kHz. But nothing compares to the moth’s 300-kHz extreme.
Since there aren’t any sounds in nature that come close, scientists hypothesize that greater wax moths evolved supersensitive ears to evade bats, their main predators. (See “‘Whispering’ Bat Evolved to Trick Prey.”)
“I think it’s a really amazing study,” said Damian Elias, a biologist at the University of California, Berkeley, who wasn’t involved in the experiment.
“Biologists make assumptions as to what types of sounds and frequencies animals should hear,” he said, but ”when you actually measure it, you’re often surprised.”
No Words to Explain It
To test the moths’ hearing, the scientists built special speakers that played increasingly higher frequencies. The team then used a laser to measure the moths’ ear movements in response to each frequency. They also assessed the electrical nerve signals sent from the moths’ ears to their brains.
These two calculations indicated whether the moths’ ears were responding to individual sounds. The results showed that the moths ended up topping out at about 300 kHz—a pitch so high that even researchers have a difficult time understanding the pinnacle.
“The problem is that because humans don’t hear that sort of frequency, we don’t have any words for it,” said study co-author James Windmill, an acoustical engineer at the University of Strathclyde in Scotland.
“There’s not that much that happens in nature that happens at those frequencies.”
Bat vs. Moth
Bats are the only animals that come close, with a hearing capability of about 212 kHz. Windmill and his team hypothesize that moths—found throughout much of the world—use their highly acute hearing to avoid bats that see them as tasty snacks.
Listen to a silver-haired bat attack an insect.
The two groups have been locked in an evolutionary arms race for generations, each trying to best the other by evolving new traits to hunt and evade. Right now, the moths are winning, said Windmill, whose study was published May 8 in Biology Letters. (Related: “Moths Jam Bat Sonar, Throw the Predators Off Course.”)
The advantage is a matter of physics, where response time and frequency are closely tied. Since moths are able to hear such high pitches, they have the ability to react to lower pitches much faster. Moths listen for a bat’s ultrasound pulses and take evasive action. (Interactive: Hear tropical bat calls.)
Moth Ears Could Inspire New Tech
Compared with a human ear, the moth ear is incredibly simple, consisting of just a few nerve cells that feed directly into the brain. The natural system is so unique that Windmill says he’s working with the military and hopes to develop microphones based on the design.
More sensitive microphones could be adapted for hearing aids and cell phones, which have what’s called the “cocktail-party problem.”
Whereas human ears are able to pick out and focus on one conversation even when there’s a lot of background noise, the microphones on most devices aren’t as targeted—meaning that Windmill’s moth-ear study could be the catalyst for technological breakthroughs. (Also see “Urban Grasshoppers Sing Louder.”)
“Evolution is a great inspiration for scientists,” noted the University of California’s Elias.
“Animals have remarkable capabilities to sense things,” he said. “They’re able to do things that human hearing and human-engineered devices are very poor at doing.”