Bats and their prey are in a constant arms race. Whereas the winged mammals home in on insects with frighteningly accurate sonar, some of their prey—such as the tiger moth—fight back with sonar clicks and even jamming signals. Now, in a series of bat-moth skirmishes (above), scientists have shown how other moths create an “acoustic illusion,” with long wing-tails that fool bats into striking the wrong place. The finding helps explain why some moths have such showy tails, and it may also provide inspiration for drones of the future.
Moth tails vary from species to species: Some have big lobes at the bottom of the hindwing instead of a distinctive tail; others have just a short protrusion. Still others have long tails that are thin strands with twisted cuplike ends. In 2015, sensory ecologist Jesse Barber of Boise State University in Idaho and colleagues discovered that some silk moths use their tails to confuse bat predators. Now, graduate student Juliette Rubin has shown just what makes the tails such effective deterrents.
Working with three species of silk moths—luna, African moon, and polyphemus—Rubin shortened or cut off some of their hindwings and glued longer or differently shaped tails to others. She then tied the moths to a string hanging from the top of a large cage and released a big brown bat (Eptesicus fuscus) inside. She used high-speed cameras and microphones to record the ensuing fight.
Moths with no tails (such as polyphemus) were easy quarry for the bats, escaping only about 27% of the time, Rubin, Barber, and colleagues report today in Science Advances. But when Rubin enlarged the polyphemus hindwing lobe, twice as many escaped the bat’s sonar, or echolocation system.
Bats going after long-tailed African moon moths got a mouthful of tail 75% of the time as the moths flitted away. Shorten the tail, and the African moon moths escaped only 45% of the time. With no tail at all, that percentage dropped to 34%. When Rubin's colleagues Chris Hamilton and Akito Kawahara at the Florida Museum of Natural History in Gainesville built a family tree of silk moths and their relatives, they realized that long tails had evolved independently several times. That’s further evidence that they are an important life-saving feature for these moths.
“The authors have demonstrated a powerful approach for understanding the diversity of moth shapes,” says Aaron Corcoran, an animal ecologist at Wake Forest University in Winston-Salem, North Carolina, who was not involved with the work. “There appear to be many different ways to trick a bat’s echolocation system.” The study also revealed how hard it was for bats to work around this deception, he adds. “The fact that the bats in the study never learned how to catch these moths, despite ample time to do so, shows how hard-wired this blind spot is in the bat’s perception.”
The findings could benefit other fields such as robotics, says Martin How, a sensory ecologist at the University of Bristol in the United Kingdom. Because the study examined the bat-moth dogfights at such a fine scale, the results could help engineers design the “bio-inspired technologies of the future,” he says, including deftly flying drones.
*Correction, 5 July, 1:45 p.m.: This article has been updated to reflect that although Juliette Rubin was the lead author of the paper, some of the work was done by other researchers.