Fireflies use music as armor against bats

firefly in the day

A macro shot of a lightning bug showing off its glow light as it takes off in flight.

A new Tel Aviv University study reveals a possible defense mechanism developed by fireflies for protection against bats that might prey on them.

According to the study, fireflies produce strong ultrasonic sounds — soundwaves that the human ear, and more importantly the fireflies themselves, cannot detect. The researchers hypothesize that these sounds are meant for the ears of bats, keeping them away from the poisonous fireflies, and thereby serving as a kind of “musical armor.”

The study was led by Professor Yossi Yovel, Head of TAU’s Sagol School of Neuroscience and a member of the School of Mechanical Engineering and the School of Zoology at the George S. Wise Faculty of Life Sciences. It was conducted in collaboration with the Vietnam Academy of Science and Technology and was published in iScience on March 19, 2021.

Fireflies are known for their unique glow, used as a mating signal. Since their bodies contain poison, the light flashes probably also serve as a warning to potential predators. This signal is also the firefly’s weakness, simply because it makes it an easy target for predators. Bats are among the fireflies’ most prevalent potential predators, and some bats have poor vision, rendering the flashing signal ineffective. This led the researchers to check whether fireflies had some additional layer of protection against bats.

Professor Yovel explains that the idea for this study came up accidentally, during a study that tracked bats’ echolocation. “We were wandering around a tropical forest with microphones capable of recording bats’ high frequencies, when suddenly, we detected unfamiliar sounds at similar frequencies, coming from fireflies,” he recalls.

“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,” adds Ksenia Krivoruchku, the PhD student who led the study.

Following the discovery, Professor Yovel’s team examined three different species of fireflies that are common in Vietnam and one Israeli species, and found that they all produce these unique ultrasonic sounds, but cannot hear them.

Have fireflies developed a defense mechanism specifically for bats? Professor Yovel emphasizes that this claim was not proved in the study, but several features do point to this conclusion. Fireflies themselves can’t hear the sound, while bats can both hear it and use it to find the fireflies, so it’s more likely that it serves as a warning signal. Krivoruochku adds that the discovery of ultrasonic sounds in fireflies is in itself an important contribution to the study of predator-prey relations.

“The idea of warning signals that the sender itself cannot detect is known from the world of plants but is quite rare among animals,” Krivoruochku concludes. “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.”

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