To escape hungry bats, these flying beetles create an ultrasonic ‘illusion’

“A lot of things fly at night,” says Harlan Gough, a wildlife biologist with the U.S. Fish and Wildlife Service. Nightfall can set the stage for an acrobatic, high-stakes aerial drama – a whirlwind of bats and their prey, each trying to outmaneuver the other by pursuing them from the air and escaping.

“For many of these insects, crossing the sky is a matter of life and death,” says Gough. Bats are skilled night hunters that use echolocation to find, track and capture their prey. “If [bats are] “As they fly through the night sky,” he says, “they send out an impulse and listen for a response.”

These ultrasonic pulses are like an acoustic flashlight: they “illuminate” the night air with a sonic search beam that allows bats to find their next snack. But insects have developed a number of strategies to avoid a bat attack.

In the latest twist in our understanding of this arms race, Gough and his colleagues describe in a new study published in Biology letters that tiger beetles—insects with large eyes, long legs, and pincer-like jaws—generate their own ultrasound in response to a bat’s ultrasonic signals. They suspect that the beetles do this to deceive their predators into thinking they are poisonous so they can fly away unharmed.

How moths use ultrasound against bats

Numerous species of moths have found ways to use bats’ ultrasound to their advantage. Many species have evolved eardrum-like structures that can detect bats’ echolocation, giving them a way to escape. Sometimes they make a quick course correction to avoid the bat approaching their position. “Another strategy,” says Gough, “is for them to fold their wings and simply fall to the ground.”

Some species of moths use a special organ on their thorax to produce their blood own Ultrasound as a reaction. One reason is to signal to the bats that they are preparing an unpleasant meal. “With this strategy,” explains Gough, “you make this noise and the bat pounces on you, but it has eaten something similar in the past and knew that it was really poisonous.” And so the bat calms down pretty well .

He says we do something similar with certain insects. “Just like when you pick up a yellow jacket as a child and pretty quickly learn not to grab anything with black and yellow stripes.” All it takes is one unpleasant experience for a bat or human to generalize their avoidance behavior.

When a bat approaches an insect, it speeds up its echolocation impulses to a “final buzz” in order to better know the current location of its prey and be able to catch it. During this buzzing, some species of moths produce so much ultrasonic noise that it interferes with bats’ ability to find them.

Gough knew that tiger beetles also produce ultrasound and wondered why – and whether they did something similar to these moths.

Dark nights, bugs and occasional fear

To study the beetles, Gough spent two summers camping in southeastern Arizona as a graduate student at the University of Florida. Every night he went to bed in his tent and set the alarm for one in the morning. Then he set out on foot, under the stars, using his headlamp to search the dark mountains and ravines for tiger beetles. “It was like a lengthy nighttime Easter egg hunt where you might find one once a week,” he remembers.

During his search, Gough came face to face with rattlesnakes. One night he heard something large shuffling in the darkness and coming closer. He was horrified. “I asked myself, ‘Who the hell else was out here in the middle of the night?'” he says. When it got within five meters, he could finally see the cause of the commotion. It was a Javelina – a pig-like herbivore. The two eyed each other in the moonlight before parting ways.

During these two summers, Gough finally managed to find seven species of tiger beetles. Each time he found one, he attached its outer shell to a thin stick with some wax and left it hanging in the air. Gough would blow a blast of air at them and send them flying. He then played an audio recording of an echolocating bat, whose ultrasound pulses accelerated as they got closer.

“When you get to that feeding sound,” Gough explains, “and the beetle knows the bat is right on its tail, it responds. And what you hear are these little clicking noises. These clicking noises are produced by the flapping wing. So it’s a very clear response to the bat’s echolocation.

A poisonous imitation

When Gough heard the stuttering of the tiger beetles’ ultrasound, he knew it was nowhere near enough to disrupt a bat’s sonar. He wondered if the beetles might be signaling to the bats that they were poisonous, so he conducted an experiment where he fed them directly to big brown bats.

“And we found that they ate all these different tiger beetles,” he says. “They ate her right up.”

Gough conducted an analysis that showed that the ultrasound pulses from tiger beetles and bear moths (not related) are acoustically similar. And because bear moths Are toxic to bats, which led Gough to a hypothesis.

“It’s likely,” he says, “that these tiger beetles are producing this.” [ultra]“That is, he thinks these beetles are mimicking the bad-tasting moths to trick the bats into not eating them either – even though they would be a perfectly tasty meal.

“I’m pretty confident in their data,” says Hannah Ter Hofstede, a biologist at the University of Windsor who was not involved in the research. “Of course I think they could do more, and they say they can do more.”

Specifically, she says a next experiment would be a good idea to find out what’s going on – “to show that if a bat attacks one of these tiger beetles in flight and it makes noise, the bats will avoid eating it.” .”

Ter Hofstede also wants to know how much spatial overlap there is between the tiger beetles and the poisonous moths, because such mimicry only works if there is “a reliable correlation between the signal and the bad taste,” she says. “If there are too many cheaters in the system, the predators won’t learn very effectively.”

Most examples of this type of mimicry are visual in nature: a tasty species deceives a predator by looks like a poisonous species. But Harlan Gough says the tiger beetles show that this also happens through sound.

“There’s just so much in the night sky that we don’t recognize because we can’t see it – it’s hidden from us. What goes on behind the curtain is really exciting.”