How Hawkmoths Use Genitalia to Produce Ultrasound and Defeat Bats
When hunting bats close in, certain male hawkmoths fight back by rasping specialized scales on their genitalia against their abdomens to unleash ultrasonic clicks, scrambling the predators’ sonar. Published November 4 in the Proceedings of the Royal Society B, research reveals this bat-busting weapon has evolved independently up to seven times across multiple lineages.
Among the species tested, 77 produced ultrasound to thwart attacks from nocturnal hunters. This defensive tactic emerged as a response to intense predatory pressure, driving distinct insect lines to arrive at separate anatomical solutions for the exact same survival threat.
The sound production relies on a patch of enlarged, football-shaped scales located on the male moth’s genital valves. These are paired structures normally used to clasp females during mating.
Three distinct anatomical strategies
The physical mechanisms fall into three clear categories. Some species rub their genital scales against a row of similar scales near the rear of the abdomen, behaving much like two combs dragged together. Others press their scales against stiff, spine-like bristles jutting from the edge of the abdomen to create a rasping noise. A third group relies on a previously unidentified feature, dragging their genital scales over a field of microscopic bumps on the underside of the insect’s body.
These mechanical differences dictate the sound properties each species produces. Moths scraping scales against spines or tiny bumps create continuous noise that effectively jams bat sonar. Meanwhile, those rubbing scales against other scales generate irregular bursts designed to startle attackers or mimic foul-tasting prey. Insects utilizing the newly identified bumpy surface demonstrate the broadest acoustic repertoire, giving them greater evolutionary flexibility.
Independent evolutionary origins
Researchers estimate this genitalia-enabled ultrasound production evolved independently at least four and as many as seven times between roughly 5 million and 30 million years ago. Paul Masonick of the Florida Museum of Natural History describes the phenomenon as a vivid example of convergent evolution. That arms race cuts both ways, as several hawkmoth lineages shifting toward twilight or daytime activity subsequently lost their specialized sound-producing machinery.
Marc Holderied of the University of Bristol in England, who was not involved in the study, notes that hawkmoths clearly have more tricks up their sleeve. Jesse Barber of the American Museum of Natural History and Akito Kawahara of the Florida Museum of Natural History contributed to research that showed moths across multiple families produce ultrasound in response to bat attacks.
Nick Dowdy of the Milwaukee Public Museum points out that anatomical constraints leave certain groups locked into certain strategies, while others retain wider adaptation options. The findings demonstrate how relentless predatory pressure shapes insect survival down to the microscopic level, continually forcing new evolutionary pathways in the night sky.
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