'Top Gun' But for Insects: These Moths' Long Tails Are Jammers for Bat Sonar

​A funny-looking moth has more in common with fighter jets than most of us would ever have guessed: The luna moth's long, fluttering tail acts like radar-distracting chaff for bats' echolocation signals, effectively misdirecting the flying mammals to an expendable part of their body. It's a scene seemingly better suited to Top Gun than the night skies of North America, but hey, the animal kingdom is no stranger to a good arms race.

If you're a flying insect, having a bat show up on your tail is assuredly more terrifying than a fighter plane. Bats' echolocation abilities have evolved over millions of years to become incredibly effective at locating and tracking prey, like the relatively noisy fluttering of a moth.

Moths aren't entirely helpless, however. Many, such as noctuid moths, have simple ears that are tuned to the sonar frequencies of the bats that prey on them. Yet close to half of nocturnal moth species don't have those bat-tracking ears. According to new research, the luna moth (Actias luna, family Saturniidae) has evolved a different defense entirely: Its swallow-like tails flap and spin in its wake, creating a confusing mess that bats end up targeting, much like a heat-seeking missile getting misdirected by aerial flares.

This video clearly features a bat's echolocation chirps and shows the poor bat missing the moth's body entirely, instead taking a largely-inconsequential ​chunk out of its tail. Credit: Barber et. al

"Bats and moths have been engaged in acoustic warfare for more than 60 million years," the authors, led by by Boise State's Jesse Barber, write in the Proceedings of the National Academy of Sciences. "Yet almost half of moth species lack bat-detecting ears and still face intense bat predation. We hypothesized that the long tails of one group of seemingly defenseless moths, saturniids, are a novel antibat strategy designed to divert bat attacks."

Acoustic jamming of bat calls isn't a new concept, as even bats themselves do it to each other. But luna moths don't exactly use the flapping of their tails to reflect sonar waves in crazy directions, kind of like how the crazy angles of the F-117 Nighthawk were designed to bounce radar signals all over the place. Instead, using a new infrared video imaging technique, Barber's team showed that those flapping tails act as a feint, throwing bats off their intended target.

The team pitted luna moths, both with tails intact and hand-removed, against big brown bats (Eptesicus fuscus), which doesn't predate on the moths and thus is less likely to have an evolved counter strategy. The result was fairly striking, with the team demonstrating "a survival advantage of ∼47 percent for moths with tails versus those that had their tails removed," which is "equivalent to the advantage conferred to moths by bat-detecting ears."

Another swing and a miss from a bat. I know the video's dark, but we're talking about high-speed infrared photography here. Not an easy feat. Credit: Barber et. al

Only 34.5 percent of the tailed moths were caught by bats, while 81.3 percent of moths without their tails were taken down. That's because, when moths had their tails intact, bats targeted their hind parts far more often—a bit more than half the time. And because a flapping moth tail isn't much to grab onto, those attacks were successful a paltry 4.2 percent of the time.

The result is pretty straightforward. "Our data clearly support the antibat function of hindwing tails in luna moths," the authors write. "Our data suggest that diversionary antibat defenses can be as successful as other acoustic strategies in this arms race."

In the end, it's a fascinating finding, but the fact that these luna moths have evolved counter-defenses to bats isn't hugely surprising. After all, we're talking about the difference between living and being eaten, and not even moths will go quietly into the night.