Tiger beetles might be mimicking the sounds of poisonous bugs so bats will avoid them

AILSA CHANG, HOST:

When night falls, a high-stakes acrobatic drama takes the stage, a swirl of bats hunting insects, trying to outmaneuver each other in aerial pursuit and escape. Science reporter Ari Daniel has the latest twist in our understanding of this arms race.

ARI DANIEL, BYLINE: In graduate school at the University of Florida, Harlan Gough got to travel the world to collect insects, including moths.

HARLAN GOUGH: It is life or death for a lot of these insects to get across the sky.

DANIEL: For moths, the death part is often due to bats, skilled nocturnal hunters that use echolocation to home in on their prey.

GOUGH: When they're kind of just cruising through the night sky, they're sending out a pulse, listening for a response, pulse.

(SOUNDBITE OF BAT SQUEAKING)

DANIEL: Pulses of ultrasound like these, which have been slowed down so we can hear them. But moths don't just let themselves be found and eaten. Many species have evolved ear drum-like structures that can detect bat echolocation, which gives them escape options. Now, some moth species produce their own ultrasound in response to warn the bats that they'll make for an unpleasant meal.

GOUGH: With that strategy, you make that sound, the bat swoops in on you but it's eaten something similar in the past and known it's really toxic. Bat just leaves you alone.

DANIEL: Once a bat closes in on its prey, it speeds up its echolocation pulses like this.

(SOUNDBITE OF BAT CHIRPING)

DANIEL: During this terminal buzz, some types of moths generate enough ultrasound noise to jam up the bat's ability to locate it. Other insects can also produce ultrasound, like tiger beetles, which have long legs, big eyes and pincer-like jaws.

GOUGH: Tiger beetles are wonderful. They are actually very good nighttime flyers, some species.

DANIEL: Gough wanted to know how these beetles use their ultrasound, so he spent two summers camping in southeast Arizona. Every night, he'd go to bed in his tent and set his alarm for 1 a.m., when he'd set out by foot under the stars to search for tiger beetles. It wasn't easy.

GOUGH: It was like a long, drawn-out, nocturnal Easter egg hunt where once in, you know, maybe a week, you'd find one possibly.

DANIEL: Gough ultimately succeeded in finding seven species of tiger beetles. He'd tether their outer shells to a thin rod and suspend them in the air. Gough would blow a puff of air at them, triggering them to fly. He'd then play an audio recording of an echolocating bat.

GOUGH: When you get to that feeding buzz, that beetle knows that bat is right on its tail, you hear these little clicks made by the beating wing. So it's a very clear response to the bat's echolocation.

DANIEL: The clicks are ultrasound. Here's what it sounds like.

(SOUNDBITE OF BEETLE BUZZING)

DANIEL: Gough knew this wasn't enough sound to jam a bat sonar. And when he fed the beetles to bats, they happily ate them, which meant they weren't toxic. So this suggested to Gough...

GOUGH: It's likely that these tiger beetles are producing the sound to sound like other similar moths.

DANIEL: That is, he believes the beetles are mimicking bad-tasting moths to trick the bats into not eating them either. Gough, who's now a biologist with U.S. Fish and Wildlife, and his colleagues published their findings in the journal Biology Letters.

HANNAH TER HOFSTEDE: I'm quite convinced by their data. Of course, I think that there's more that they could do, and they say that there's more that they can do.

DANIEL: Hannah ter Hofstede is a biologist at the University of Windsor who wasn't involved in the research. She says there's an obvious next experiment to really nail down what's happening.

TER HOFSTEDE: To show that if a bat is attacking one of these tiger beetles in flight and they produce the sounds, that the bats will avoid eating them.

DANIEL: Most examples of this kind of mimicry are visual. A tasty species tricks a predator by looking like a toxic species. But Harlan Gough says the tiger beetles show it happens with sound, too.

GOUGH: In the night sky, there's just so much that we don't realize because we can't see it, you know? And it is hidden to us.

DANIEL: To reveal it, you just have to listen. For NPR News, Ari Daniel.

(SOUNDBITE OF SLVR SONG, "BACK N FORTH" ) Transcript provided by NPR, Copyright NPR.