Hawkmoths have been fighting an acoustic war with bats for millions of years, and a new study shows that some of them built their countermeasures in a place nobody would think to look: the male genitalia. Researchers examined 143 hawkmoth species and found that 77 could answer simulated bat attacks with ultrasound, produced through three distinct scraping systems.
The surprise is not simply that the moths make noise. The team found that different hawkmoth lineages repeatedly arrived at the same broad defense while evolving different anatomical hardware to do it. In other words, evolution did not invent one tiny anti-bat instrument and hand it down. It assembled several versions independently, up to seven times over roughly the last 30 million years.
Three microscopic instruments, one very hungry audience
The study, published November 4 in Proceedings of the Royal Society B, combines acoustic recordings, high-resolution scanning electron microscopy, micro-CT imaging and an evolutionary family tree. That mix let the researchers connect the sounds moths made with the exact structures making them.
All three systems begin with enlarged scraper scales on the male genital valves. What those scales rub against is where the engineering branches.
In the scale-on-scale system, the genital scraper moves across a second row of specialized scales near the end of the abdomen. In the scale-on-spine system, it runs over stiff spines. The newly described scale-on-nodule system drags the scraper across a field of tiny raised bumps on the underside of the abdomen. Each setup works like a microscopic washboard, turning rapid body movement into pulses above the range of human hearing.
The study’s anatomy figure makes the differences unusually easy to see. Electron-microscope images reveal the textures of the scraper and file surfaces, while 3D reconstructions show how the paired genital valves move against the abdomen. This is one of those cases where the scientific diagram is also the payoff: three lineages, three pieces of biological hardware, and the same problem waiting in the dark.
Why make ultrasound when a bat is closing in?
Bats hunt many night-flying insects by sending out ultrasonic calls and reading the returning echoes. A moth that can hear those calls gains a warning, but hearing alone does not end the chase. Some moths dive or turn sharply. Others broadcast ultrasound of their own.
Those defensive sounds can serve several purposes. They may startle an inexperienced predator, advertise that a moth is unpleasant to eat, imitate the warning sounds of genuinely unpalatable species, or interfere with the bat’s ability to measure its target. The last option is sonar jamming: if the moth produces enough sound at the right moments, the bat’s acoustic picture becomes harder to use.
The new research does not claim that every ultrasonic hawkmoth jams sonar equally well. That distinction matters. The signals from moths with hearing organs generally showed more of the timing characteristics associated with jamming potential, including a higher duty cycle. Some non-hearing species produced different signals that may work more as a startle or warning tactic. The team also encountered one ultrasound-producing species without an obvious genital scraping structure, a reminder that the family may still be hiding more acoustic tricks.
Evolution kept rebuilding the weapon
By mapping the behavior and anatomy onto the hawkmoth family tree, the researchers inferred between four and seven independent origins of the response to bat calls. The three mechanical systems also arose in different branches. That repeated pattern is a strong example of convergent evolution: unrelated or distantly related groups facing the same pressure and evolving comparable solutions.
The timing is equally suggestive. The moth systems emerged during a long period when echolocating bats were diversifying and improving their aerial hunting. Every advance by the predator creates pressure for a countermeasure, which creates pressure for a better predator. The result is less a straight evolutionary ladder than an arms race conducted in frequencies most humans cannot hear.
There may also be a twist in how the hardware began. Some researchers suspect genital sound-making structures originally had a role in courtship and were later repurposed for defense. The new paper focuses on the anti-bat response and the repeated evolution of its mechanisms, so that courtship-first idea remains a hypothesis rather than the study’s conclusion.
What the study actually answers
The clearest answer is anatomical. Hawkmoths are not all producing defensive ultrasound with one inherited device. Males in different lineages scrape genital scales against scales, spines or nodules on the abdomen, creating acoustically distinct signals. Those systems evolved repeatedly, and their sound properties track both their shapes and whether the moths can hear approaching bats.
That is a much richer story than “moths make weird noises.” It shows how an ancient predator-prey contest can repeatedly transform the same part of an animal into different tools. For additional reporting and images, see Science News and Smithsonian. An earlier HHMI BioInteractive field video featuring study coauthor Jesse Barber offers useful background on how moth ultrasound can jam sonar or mimic warning signals, but it does not depict this new experiment or its three anatomical systems.
Image credit: Figure 2 from Paul K. Masonick, Maja Petricic, Alessandro Giusti, Christian D. Couch, Jesse R. Barber and Akito Y. Kawahara, “The repeated evolution of anti-bat bioacoustics in hawkmoths,” Proceedings of the Royal Society B (2026), used under the Creative Commons Attribution 4.0 license.
