Fireflies use invisible 'musical armor' against bats, study suggests

Because the sounds are ultrasonic, they cannot be detected by either humans or fireflies themselves.

Firefly. (photo credit: BRANDON ALMS)
Firefly.
(photo credit: BRANDON ALMS)
 With their visible lights that give them their name, fireflies are possibly one of the most easily noticeable type of insects. But according to a new study, these bright bugs may also have a secret defense system that is invisible to the human eye – and more importantly, the ear.
According to a new study led by Prof. Yossi Yovel, head of Tel Aviv University's Sagol School of Neuroscience and member of the School of Mechanical Engineering and the School of Zoology at the George S. Wise Faculty of Life Sciences, fireflies use ultrasonic sounds as a sort of "musical armor."
Because the sounds are ultrasonic, they cannot be detected by either humans or fireflies themselves. But they can be detected by the insects' most prevalent predator: Bats.
Even more surprising than the existence of this defense mechanism is the fact that it was discovered by complete accident.
In a separate study led by PhD student Ksenia Krivoruchku, who was also the lead author of the current paper, scientists were looking to track bats' echolocation. And it was here, using microphones to track the bats' high frequencies, that the researchers detected unfamiliar sounds from the fireflies.
"In-depth research using high-speed video revealed that the fireflies produce the sound by moving their wings, and that the fireflies themselves can't hear this frequency. Consequently we hypothesized that the sound is not intended for any internal communication within the species," Krivoruchku said in a statement.
Yovel's team studied four different firefly species - three from Vietnam and one from Israel - and found that all of them did indeed produce these sounds.
Of course, there isn't definitive evidence that the sounds are meant to be a defense mechanism made specifically for bats, but Yovel pointed to a number of features that seem to indicate that this is the case. Most notable, however, is the fact that this should essentially serve as a warning signal for the bats.
Fireflies use their unique and famous glow as a mating signal, but they also likely serve as a warning to predators that their bodies contain poison, similar to the colors on a poison dart frog. But this warning doesn't work on bats, since while bats are not blind despite popular misconception, many do have very poor vision, so the warning signal doesn't register. 
And if this is true, it would be a major contribution to the predator-prey dynamic.
"The idea of warning signals that the sender itself cannot detect is known from the world of plants but is quite rare among animals," Krivoruchku said. 
"Our discovery of the 'musical battle' between fireflies and bats may pave the way for further research, and possibly the discovery of a new defense mechanism developed by animals against potential predators."
The findings of the study were published in the academic journal iScience.