Butterflies enlist additional troops in an evolving arms race

While a clear night sky may seem calm and peaceful to us, void of anything but stars, this nocturnal world is filled with a shrill cacophony of sound just beyond our ability to hear. Bats pierce the shadows with ultrasonic pulses that allow them to construct an auditory map of their surroundings, bad news for moths, one of their favorite foods.

However, not all moths are defenseless prey. Some emit their own ultrasonic signals that scare bats into breaking off their pursuit. Many moths that contain bitter toxins avoid capture altogether by producing distinct sounds that alert bats to their bad taste. Others hide in a veil of sonar blocking static electricity that hampers bats’ ability to find them by echolocation (locating them with reflected sound).

These types of auditory defense mechanisms in moths were thought to be relatively rare, known only from tiger moths, moths, and a single species of geometric moth. But one US National Science Foundation– sustained study published in the journal PNAS shows that ultrasound-producing butterflies are much more widespread than previously thought, adding three newly discovered sound-producing organs, eight new subfamilies and potentially thousands of species to the list.

“It’s not just tiger moths and hawkmoths that do this. There are tons of moths that create ultrasonic sounds, and we know next to nothing about them,” the author said. lead author Akito Kawahara, curator at Florida Museum of Natural History.

The researchers also wanted to understand how these sounds might converge across moth species. In the same way that non-poisonous butterflies mimic the colors and wing patterns of less palatable species, butterflies that don’t benefit from built-in toxins can copy the pitch and timbre of truly unpalatable relatives.

After collecting and studying thousands of moths for more than a decade in Ecuador, French Guiana, Mozambique and Malaysian Borneo, the researchers spent the last two weeks in Ecuador, where they recorded the alarm calls of every butterfly they could catch. Then they analyzed those recordings with the help of a theoretical physicist and a machine learning algorithm that scrutinized each note, looking for similarities.

The program revealed what, until now, other researchers had only guessed at: moth species don’t act as individual composers, each with their own calling card and distinct style. Instead, a small number of butterflies derive their own scores, which other butterflies appear to replicate in rings of complex acoustic mimicry.

Lead author Jesse Barber, a biologist at Boise State University, says more work is needed to uncover the exact nature of these sounds, but he suspects the pioneer moths at the center of these rings are likely harmful, while fringe imitators are simply fake advertisers. “If these results materialize, it will likely be the largest set of mimicry complexes on Earth,” he said.

Jodie Jawor, Program Director of NSF’s Integrative Organ Systems Division, added, “Findings like these not only help us understand the incredible complexity and diversity of animal behavior, but also set the stage for the development of technologies that humans can use.”

Martin E. Berry