Distracting Tails

Luna moths use their long tails to throw bats off their trail.

Feb 17, 2015
Jenny Rood

WIKIMEDIA, GEOFF GALLICE

In the first experimental test of a 112-year-old theory, the tails of luna moths helped save the insects from hunting bats by distracting the flying mammals’ sonar, researchers reported this week (February 17) in PNAS.

The function of the North American moths’ two graceful nearly 4-cm-long tails has long been a topic of scientific study. They are not required for flight and are unlikely to play a role in attracting mates, as the insects are nocturnal and do not appear to be selective about their sexual partners. In 1903, entomologist Archibald Weeks suggested that the tails might create air patterns similar to those generated by wings that could confuse bats using echolocation to hunt.

To test this idea, researchers from Boise State University, the University of Florida, and Northeast Ohio Medical University affixed 162 luna moths to the ceiling with fishing line, then used high-speed infrared cameras and ultrasonic recorders to capture information on eight brown bats attacking the moths. Of the 87 moths with intact tails, 34.5 percent were nabbed by bats. By contrast, 81 percent of the 75 tailless luna moths in the study were eaten. The researchers also noted that the bats often aimed for the tails of intact moths, and in the vast majority of these attacks, the moths were able to escape.

Further investigation revealed that the echo signature created by the moths’ tails spinning through the air closely mimics that of wing beats, suggesting that the tails provide a life-saving decoy. By analyzing the tail lengths of related moths, the researchers found that similar tails had evolved independently at least four times. “Our data suggest that diversionary anti-bat defenses can be as successful as other acoustic strategies in this arms race,” the authors wrote in their paper.