Deaf ermine moths outsmart predatory bats using ultrasonics
Turns out, moths have a unique sound-producing mechanism known as ‘aeroelastic tymbal.’
Scientists at the University of Bristol uncovered how ermine moths use ultrasonic clicks using specialized structures in their wings as a defense against bats.
The moths produce clicks via tiny corrugated membranes in their hindwings. The ridges snap through during wing folding, amplifying the sound.
This unique sound-producing mechanism, known as an ‘aeroelastic tymbal,’ operates passively in flight, serving as an evolutionary adaptation against predators.
While many animals like rattlesnakes and poison dart frogs are known to produce sounds to let the potential predators around them know of an upcoming poisonous attack, the case of ermine moths is more so interesting.
Due to the absence of hearing organs, these creatures remain oblivious to their distinctive defense mechanism and, therefore, also lack the ability to regulate it through muscular action.
So how does ‘acoustic defense’ work?
Ermine moths are typically tiny, with a wingspan ranging from one to two centimeters. They are often white or light-colored. An interesting thing happens when they fold their wings while flying.
The small parts in their wings snap, creating a strong sound. Researchers explained that snapping these tiny parts makes a sound-producing organ called an ‘aeroelastic tymbal.’
The snap-through buckling events function similarly to drum beats at the edge of a tymbal drum. This process excites a significantly more extensive section of the wing, causing it to vibrate and emit sound.
The outcome is that these small tymbals, each just a few millimeters in size, can generate ultrasound at a level comparable to a lively human conversation.
Essentially, the snapping mechanism amplifies the sound production, allowing the moths to create ultrasound signals effectively.
“Our goal in this research was to understand how the corrugations in these tymbals can buckle and snap through in a choreographed way to produce a chain of broadband clicks,” said Marc Holderied, Professor of Sensory Biology at the School of Biological Sciences at Bristol, in a press release.
“With this study, we unfolded the biomechanics that triggers the buckling sequence and shed light on how the clicking sounds are emitted through tymbal resonance,” added Professor Holderied.
To understand how aeroelastic tymbals work, the study’s first author, Hernando Mendoza Nava, used the latest techniques in biology and engineering.
First, he studied the wing’s shape and material properties. Then, he used this information to create computer simulations that mimicked the moth’s snapping and sound production.
These simulations matched the actual moth signals in terms of frequency, structure, how loud they were, and in which direction they traveled.
Rainer Groh, Senior Lecturer in Digital Engineering of Structures at Bristol, added: “The integration of various methods across the sciences with a consistent information flow across discipline boundaries in the spirit of ‘team science’ is what made this study unique and a success.”
“In addition, without the amazing modern capabilities in imaging, data analysis, and computation, uncovering the mechanics of this complex biological phenomenon would not have been possible,” added Groh.
The study was published in the Proceedings of the National Academy of Sciences on February 5.
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