They sure know how to put on a show at nights – fireflies are striking with their glow-in-the-dark feature. But have you ever stopped and wondered how these glowing insects defend themselves against predators? A trailblazing TAU study reveals that fireflies produce strong ultrasonic sounds that may potentially work to deter bats, serving as a ‘musical armor’ against these predators. The discovery of such a ‘musical battle’ between fireflies and bats may pave the way for further research, and the discovery of a new defense mechanism developed by animals against their predators.
According to the study, the 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, in fact, meant for the ears of the bats, keeping them away from the poisonous fireflies, and thereby serving as a kind of ‘musical armor’.
The study was led by Prof. Yossi Yovel, Head of the 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 (VAST) and has been published in iScience.
Fireflies are known for their unique, all-year glow, which is effective as a mating signal. Their bodies contain poison, and so the light flashes probably also serve as an aposematic signal, a warning to potential predators. At the same time, this signal is also the firefly’s weakness, as 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 prompted the researchers to check whether fireflies were equipped with an additional layer of protection against bats.
The idea for this study came up accidentally, during a study that tracked bats’ echolocation. Ksenia Krivoruchku, the PhD student who led the study recalls, “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.
“In-depth research, using high-speed video, revealed that the fireflies produce the sound by moving their wings, and that the fireflies themselves are incapable of hearing this frequency. Consequently, we hypothesized that the sound is not intended for internal communication within the species.”
Following this discovery, the team at Prof. Yovel’s laboratory examined three different species of fireflies that are common in Vietnam (Curtos, Luciola and Sclerotia), in addition to one Israeli species (Lampyroidea). It was found that they all produce these unique ultrasonic sounds, and that they are all unable hear them.
Prof. Yovel says that it is premature to conclude that fireflies have developed a special defense mechanism specifically targeting bats, there are indications that this may be the case. The fact that the fireflies themselves are unable to hear the sound, while bats can both hear it and use it to detect the fireflies, makes it more likely that these ultrasonic sounds serve as a warning signal.
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 says “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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