Hawkmoths Deploy Genital Sound Systems to Deflect Nighttime Bat Attacks
When predatory bats close in during nighttime hunts, male hawkmoths fight back by rubbing specialized genital scales against their abdomens to unleash ultrasonic clicks that scramble the predator’s sonar, according to research published November 4 in the Proceedings of the Royal Society B. Sciencenews.org reported that this acoustic defense has evolved independently up to seven times across multiple lineages, revealing a complex evolutionary arms race playing out silently overhead.
Researchers Track Ultrasonic Defenses in Hawkmoths
For more than a decade, sensory ecologist Jesse Barber—now at the American Museum of Natural History in New York City—and entomologist Akito Kawahara of the Florida Museum of Natural History in Gainesville have tracked how various moth families generate ultrasound during bat attacks. Their prior work documented sonic defenses in tiger moths, fruit-piercing moths, geometer moths, and jewel caterpillar moths, alongside several beetles and fireflies. Yet the precise mechanisms among hawkmoths—a family of roughly 1,600 nocturnal, torpedo-shaped insects that hover at flowers—remained poorly mapped. To uncover how these acoustic systems function, Barber and Kawahara joined forces with Florida museum evolutionary biologist Paul Masonick and their research team. They combined high-fidelity audio recordings of male hawkmoths reacting to simulated bat calls with high-resolution microscopy of preserved specimens from overlapping species.
Among 143 species tested in the study, 77 produced ultrasound through three distinct anatomical strategies. Every method relies on a patch of enlarged, football-shaped scales located on the male's genital valves, which are paired structures utilized to clasp females during copulation. However, what those specialized scales scrape against differs significantly. A third group employs a previously unidentified apparatus: a microscopic field of bumpy ridges on the insect's underside.
Mechanical Variation Shapes Ultrasonic Jamming Capabilities
These structural differences dictate the precise acoustic properties of the generated sound waves. Moths that scrape their genital scales against spines or the newly discovered microscopic bumps produce longer, continuous noises with high potential to jam bat sonar. Conversely, individuals that rub scales against other scales create irregular bursts designed to startle predators or mimic warning sounds associated with foul-tasting prey. As Nick Dowdy, an evolutionary biologist at the Milwaukee Public Museum who was not involved in the research, observed, moths utilizing the newly identified bumpy surface possess the broadest acoustic repertoire, offering greater flexibility for evolving novel defenses compared to lineages locked into rigid anatomical strategies.
The research team estimates that genitalia-enabled ultrasound production emerged independently between 5 million and 30 million years ago. Masonick characterized the phenomenon as a clear example of convergent evolution driven by intense predatory pressure from bats. Yet this evolutionary arms race operates in both directions. Several hawkmoth lineages that transitioned toward twilight or daytime activity subsequently lost their specialized sound-producing machinery, demonstrating how deeply bat predation molds insect evolution.
