Male hawkmoths have repeatedly evolved ultrasonic genitals to jam the sonar of hunting bats, according to a study published on Wednesday 4 November in Proceedings of the Royal Society B.
Researchers led by Paul Masonick at the Florida Museum of Natural History say the sound-making trick has arisen independently at least four times and as many as seven, Science News reported. The estimated dates run from roughly 5 million to 30 million years ago.
As Vice put it, this is a case of nature refusing to leave a good idea alone. Its writer imagined a bat’s point of view: swooping in for a snack, only to have the snack’s genitals start screaming at you.
Three ways to make a racket
The moths do not literally scream, but the effect is similar. Males rub specialised scales on their genital valves against parts of the abdomen, producing bursts of ultrasound that bats can hear.
The team found three separate set-ups. ScienceAlert reported that scale-on-scale tends to give shorter, intermittent bursts. Scale-on-spine gives longer, more sustained emissions, and Vice adds a third, scale-on-nodule, where scales are scraped over tiny bumps.
The differences matter. The sustained sounds were the ones most likely to have the acoustic features linked to scrambling bat sonar, ScienceAlert said.
According to Archyde’s account of the Science News report, the team tested 143 species and 77 of them made ultrasound. Vice put the number examined at more than 120, so the figures vary between outlets. Phys.org said the team also looked at the evolutionary relationships of 310 hawkmoth species to trace the history.
The team recorded male hawkmoths reacting to bat calls and compared the sounds with imaging of preserved specimens. Phys.org reported that they also used gentle handling to simulate capture by a predator.
Ears, no ears
Hearing appears to be part of the story. Moths with hearing organs generally made sounds with a greater potential to interfere with bat sonar. The researchers say that suggests the ability to detect bat calls may be closely linked to producing anti-bat ultrasound.
Species without hearing organs were not defenceless. Some made ultrasound when touched, which fits Vice’s description of shorter bursts triggered only once a predator has already grabbed them.
Hawkmoth hearing is odd in its own right. In remarks carried by News Beep, Masonick said: “They hear with their mouths and they stridulate [produce sound] with their genitals.”
He added that hawkmoths are palatable to bats, unlike toxic moths such as tiger moths. Bats rarely just bite a big moth out of the air, he said. They tend to wrap their wings and tail membranes round it first, which gives the moth a moment to make noise.
The moths may not always jam the bat’s sonar. Science writer David Bradley noted that, even if the sound does not jam echolocation, a sudden burst might startle young or naive bats just before they strike.
Several hawkmoth lineages that moved to twilight or daytime activity later lost their sound-making machinery, Science News said. Masonick told the outlet: “It goes to show how intense bat predation is on insects.”
The study focused on males. Some females also make ultrasound, Scimex reported, by pulling their genitalia inward and rubbing internal structures together. Science News said female sound production is too poorly documented for a systematic comparison.
That is the next puzzle. According to News Beep, Masonick says the question now is what the females are doing.
Sources: Vice, Science News, ScienceAlert, Phys.org, Archyde, News Beep, Sciencebase, Scimex
This story was compiled by the MDW Newsdesk with AI-assisted tools, using the reporting credited above.
