Hawkmoths’ genital defenses evolved at least four times

The team paired audio recordings of males responding to bat calls with high-resolution images of preserved specimens from overlapping species. The analysis centered on males, even though some females also produce ultrasound, because female sound production remains too poorly documented for systematic analysis.

All three male sound-producing systems rely on a patch of enlarged, football-shaped scales on the genital valves, the paired structures used to clasp females during mating. The surface rubbed against them varies.

• Scales against matching scales near the rear of the abdomen: Moths produce irregular bursts. These may startle attackers or mimic the warning calls of foul-tasting prey.
• Scales against stiff spines jutting from the abdomen’s edge: Moths tend to produce more continuous noise, which has greater potential to jam bat sonar.
• Scales against microscopic bumps on the insect’s underside: This previously unidentified part of the sound-producing apparatus also tends to yield continuous noise, but it gives these moths the broadest acoustic repertoire.

Different surfaces, different sounds.

Even close relatives using the bumpy surface can sound quite different. Nick Dowdy, an evolutionary biologist at the Milwaukee Public Museum who had no role in the research, said that flexibility could give moths more options for evolving new defenses. Other groups may be more constrained by their anatomy and remain tied to narrower strategies.

Why did this defense evolve more than once?

The evolutionary count remains an estimate, ranging from four to seven independent origins. Masonick called the pattern a vivid example of convergent evolution: the same threat repeatedly drove similar behavior through different anatomical routes.

The contest did not run in only one direction. Several hawkmoth lineages that shifted toward twilight or daytime activity subsequently lost their specialized sound-producing machinery.

“It goes to show how intense bat predation is on insects,” Masonick said. “It’s been a major driver of insect evolution.”

What does this change for understanding bat defenses?

The finding changes the picture for researchers studying bat defenses: one widespread moth threat has produced several acoustic answers, not one. The authors suggest that the nightly exchanges beyond human hearing may be far more varied than scientists realized.

That variability matters because different surfaces create different sounds. Continuous noise may interfere more directly with sonar, while irregular bursts may work through surprise or deception. Those remain proposed functions, not guaranteed outcomes for every species.

Still, the work leaves the female side of the story largely uncharted, and its evolutionary count is an estimate rather than an exact historical tally. The mechanisms and sounds are documented; their proposed effects on bats are not settled facts.