When you leave the city limits and head out into the woods, what do you hear? While you may initially say “nothing,” think a little bit harder. There are birds singing, crickets chirping, frogs croaking, and a variety of other organisms making a great deal of noise so that they can be heard over all of the other animals shouting out pick up lines and find a mate of their own. Of course, while making sound is great while looking for love, it also alerts predators about where they can find a meal.
A group of researchers led by Fernando Montealegre-Z of the University of Lincoln have discovered a new insect genus in South America that uses a unique ultrasonic mating call, which is the highest-pitch call ever discovered. This frequency allows them to better hide from bats and other predators. The results have been published in PLOS ONE.
Located in Colombia and Ecuador, the genus has been labeled Supersonus, as an homage to the males’ unique call that is a full order of magnitude outside the range of human hearing. Humans typically have an auditory range of 50 Hz–20 kHz, while the females communicate in the 5 kHz-30 kHz. The males, on the other hand, vocalize up to 150 kHz.
The three species in Supersonus belong to the Tettigoniidae family, commonly referred to as katydids or bush crickets, which create sound from rubbing their wings together. “To call distant females, male katydids produce songs by ‘stridulation’ where one wing (the scraper) rubs against a row of ‘teeth’ on the other wing,” Montealegre-Z explained in a press release. “The scraper is next to a vibrating drum that acts like a speaker. The forewings and drums are unusually reduced in size in the Supersonus species, yet they still manage to be highly ultrasonic and very loud.”
Using sophisticated equipment, Montealegre-Z’s team was able to determine that Supersonus alters the position of its wings in order to act like a speaker capable of radiating such high frequencies. While some katydids are able to fly, many don’t. Over time, the wings of Supersonus became too small for flight, which makes it harder to avoid predators like bats.
However, that same trait may have given them a different ability to communicate in ranges much too high for predators. While the bats are still able to locate the insects through echolocation, the call of the Supersonus is at the upper limit of bat hearing. A 150 kHz call will not carry as well across large distances, making it much harder to make out, obscuring the insect’s position. Additionally, the insect can hear the bat’s ultrasonic echolocation call, alerting the insects about the predator’s presence.
“These insects can produce, and hear, loud ultrasonic calls in air. Understanding how nature’s systems do this can give us inspiration for our engineered ultrasonics,” co-author James Windmill added. Some uses for ultrasonic technologies include biomedical imaging, non-destructive testing of material integrity, sonar, and identification locating systems.
