Most audiologists know that humans hear from about 20 Hz to 20 kHz and as we age our frequency range might go down somewhat, according to some sources, to about 12-15 kHz. It is, however, no fun to know the same things as your colleagues. For your next audiological trivia encounter consider a challenge of, “What species has hearing up to 300 kHz?” The audience or colleagues will be in amazement and not believe that anything or anybody hears at that high of a frequency. While our favorite audiology trivia game will not be returning to our annual American Academy of Audiology Convention anytime soon, knowing the best audiology facts can win those other trivia contests!
Dolfins are thought to have 10 times the sensitivity of humans and also hear at a very high frequency hearing range at about 160 kHz (extra trivia to dazzle friends) that is used for communication and echolocation. They have very small ears behind the eyes so many people don’t give their hearing much of a thought. They can hear both in the water and on the surface of it. For many years, Bats were thought to have the highest frequency hearing at 217 kHz (more dazzling trivia). Of course, Bats also use their high frequency hearing for echolocation. By sending out high frequency call and analyzing echoes that come back, bats and the dolfins can essentially “see” the whole picture of the world around them. Scientists have long thought that bats judge the size of a nearby object based on the strength of this echo, but a new study shows that echo intensity alone does not paint the whole picture. Castro (2011) suggests that what is really important to the bats, is an echo parameter called sonar aperture — the spread of angles from which echoes impinge on the bats’ ears, with a larger spread indicating a larger object. Now you might win the contest by knowing about about bat hearing and how the use echolocation as well as the limits of their hearing but you would be a tough contestant by knowing that the Greater Wax Moth hears up to 300 kHz. While the workings of the echolocation of bats with their high frequency sensitivity is interesting, their frequency range capability perils in the face of the Greater Wax Moth.
Here’s the Deal…….
Research in Glasgow, Scotland, UK supports the notion that these moths hear at an incredible high frequency. Dr. James Windmill of the University of Strathclydethe’s University’s Centre for Ultrasonic Engineering, has identified the extraordinary sensory characteristics of the moth, paving the way for developments in air-couple ultrasound. Windmill said, “We are extremely surprised to find that the moth is capable of hearing sound frequencies at this level and we hope to use the findings to better understand air-coupled ultrasound.” He further said, “It’s not entirely clear how the moths have developed to be able to hear at such a high frequency, but it is possible that they have had to improve the communication between each other to avoid capture from their natural predator, the bat, which use similar sounds.” Prior to the Windmill team’s research others had tested the hearing of the greater wax moth but gave up as the frequency range approached 100 kHz. The use of a vibrometer to measure the vibrations of the ear in response to sound waves as well as the electrical signals in the auditory nerve, then watched as the sound got more n more high frequency with the response finally vanishing at 300 kHz.
Do we Really Care?
So, this is nice, but why do we care about the Greater Wax Moth having a frequency range for hearing range up to 300 kHz? The use of ultrasound in air is extremely difficult and as high frequency signals are significantly quickly weakened in the air. Other animals such as bats are known to use ultrasound to communicate and now it is clear that moths are capable of even more advanced use of sound. The research findings will allow the Dr. Windmill and his colleagues to further develop their understanding of ultrasound and how to transmit and receive ultrasonic pulses travelling in air. With frequency sensitivity that is unparalleled in the animal kingdom, this moth is ready for any echolocation call adaptations made by the bat in the on-going bat–moth evolutionary war.
Dr Windmill’s multi-disciplinary research team is now working to apply the biological study of this, and other insect ears to the design of micro-scale acoustic systems. It is hoped that by studying the unprecedented capabilities of the moth’s ear, the team can produce new technological innovations, such as miniature microphones. Click here or on the Moth for a video of the Greater Wax Moth story.
Castro, J. (2011). New picture of bats acoustic sense emerges. Live Science. Retrieved January 17, 2017.
Moir, H., Jackson, J., & Windmill, J. (2011). Extremely high frequency sensitivity in a ‘simple’ ear. Biology Letters, 2013; 9 (4). Retrieved January 17, 2017.
GeoBeats news (2013). Moths can hear ultrasonic sound. YouTube.com. Retrieved January 17, 2017.