Hawkmoths evolved ultrasound-producing genitalia as a bat defence up to seven times

Male hawkmoths have repeatedly evolved the ability to make ultrasound by scraping scales on their genitalia against other parts of the abdomen, according to a study in the Proceedings of the Royal Society B. Of 143 species tested, 77 produced ultrasound, and the sound-making apparatus appears to have arisen independently at least four and as many as seven times. The clicks can interfere with the sonar that bats use to track prey.

Testing 143 species

The team was led by Jesse Barber, now at the American Museum of Natural History, and Akito Kawahara of the Florida Museum of Natural History, with evolutionary biologist Paul Masonick of the same museum. They combined audio recordings of male hawkmoths responding to bat calls with high-resolution imaging of preserved specimens from overlapping species.

The work focused on males. Some females also produce ultrasound, but the researchers considered the documentation of female sound production too sparse for systematic comparison.

It extends more than a decade of earlier work by Barber and Kawahara, which showed that moths in several families, including tiger moths and geometer moths, respond to bat attacks with ultrasound. Some beetles and fireflies do likewise.

Three ways to make a sound

All three mechanisms depend on a patch of enlarged, football-shaped scales on the genital valves, the paired structures males use to clasp females during mating. What differs is the surface those scales are drawn across:

• a row of matching scales near the rear of the abdomen;
• stiff spines projecting from the abdominal edge;
• a field of microscopic bumps on the underside, a part of the sound-making apparatus not previously identified.

Anatomy shapes the acoustic signal

The mechanical differences show up in the sounds. Moths that rub scales against spines or bumps tend to produce more continuous noise, which has greater potential to jam bat sonar. Those that rub scales against scales make irregular bursts. The authors suggest such bursts may startle attackers or imitate the warning calls of distasteful prey, although the source does not report tests of these functions.

Species using the bumpy surface showed the widest range of sounds, with even close relatives differing markedly. Nick Dowdy, an evolutionary biologist at the Milwaukee Public Museum who was not involved, noted that this flexibility could give such lineages more room to evolve new defences. Groups with other anatomies may be more tightly constrained, he said, leaving them "locked into certain strategies".

Convergence, and loss

The authors estimate that the trait evolved between roughly 5 million and 30 million years ago. Masonick describes it as a clear case of convergent evolution, in which one predatory threat drove similar behaviour through different anatomical routes.

The pattern was not simply one of gain. Several hawkmoth lineages that moved towards twilight or daytime activity later lost their specialised sound-producing structures, which is consistent with bat predation being the main selective force behind the trait.

Why it matters

The results suggest that nightly acoustic contests between bats and insects are more varied than previously assumed. Marc Holderied, a bioacoustics researcher at the University of Bristol who was not involved, said hawkmoths as a whole appear to have "more tricks up their sleeve".

The comparison of anatomy and acoustics across many species provides a framework for testing how particular sound types affect bat hunting success, and for exploring whether other insect groups hold similarly hidden diversity. Female sound production, which the study left aside, remains an obvious gap to fill.

Source: How hawkmoths turned their genitals into bat-busting weapons (Science News, 4 November 2026).

Image: AI-generated illustration.