Science and Tech

Bats love beetles. But some of these have a secret weapon: pretending they are poisonous moths

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Every night bats engage in a battle of evolutionary wits with their prey. These mammals have a natural “sonar” that allows them to fly without depending on their sight, but the insects they seek are not short on tools.

An example of this is the tiger beetle.

Sonic camouflage. For several decades we have known that tiger beetles (Cicindelinae) are capable of emitting a high-pitched sound and that they tend to do so in response to the presence of bats, one of their main predators. Now a team of researchers think you know why They do it: camouflage themselves.

The beetles would be, according to the hypothesis postulated by the team, imitating the sound of another insect, a type of moth. A type of moth that bats tend to exclude from their diet.

Tiger beetles. Tiger beetles make up a taxonomic family, the cicindelinos (Cicindelinae). As is often the case among Coleoptera, this is a large family, with around 3,000 known species grouped into different genera.

This is the only family of beetles whose members emit this type of ultrasound, which is more common among moths. Approximately one in five species Moths are capable of generating ultrasound.

At the laboratory. To test your hypothesis, The team first analyzed Yes, indeed, the beetles emitted their sound in response to the presence of their predators. They verified that this was the case with recordings of the sounds emitted by the echolocation system of these mammals.

Upon hearing the “attack” sound of the bats, specimens of seven of the 20 species analyzed by the team moved their wings in such a way that they generated a response sound. For humans, this movement would cause a mere hum, but its high frequencies would be picked up by bats.

Discarding hypotheses. Now, the question of why they made those sounds in response to the bat attack was not obvious. Emitting a perceptible sound to your predators as soon as you detect their presence does not seem like a good idea a priori, so there must have been some reason behind this strategy.

One possibility is that they used it to interfere with the bats’ echolocation system. The team ruled this out. since the frequency was too “simple” for it.

Sound aposematism. Perhaps it was a strategy of aposemitism or, more specifically, sonorous aposematism. Aposemitism consists of sending a danger signal to predators. Generally this consists of bright and striking colors that indicate that an animal is poisonous. These signals could also be counterintuitive since they make the animal more attractive, but it is about sending a message, a “stay away.”

Many moths generate chemicals that are toxic or at least harmful to bats. The beetles could be using sound signals in a context where visual signals don’t make much sense. But these beetles are not toxic or harmful, the team found.

But aposemitism has a trick. There are numerous species that are not harmful but thanks to their striking coloring they appear to be so. These beetles would be doing something similar: by pretending to be toxic moths, they would deceive the bats. so as not to consume them.

Evolutionary arms race. Although there are few insects capable of responding to the sounds of bats, there are more that can detect them. Especially among moths.

So much so that moths and bats have been involved in an arms race for millennia, with bats changing the frequency of their echolocation and moths expanding their hearing ranges.

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Image | Muhammad Mahdi Karim / Todd Cravens

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