Most bat species are nocturnal hunters and use high frequency sounds to locate prey in the dark. Many moths are also nocturnal foragers and are the favorite foods of hungry bats. However, recent research shows that moths are far from defenseless targets of successful bat echolocation. Some emit their own ultrasonic signals that can startle a bat into giving up the hunt, convince the bat that the butterfly is poisonous, or can even surround the butterfly in a shroud of static-blocking sonar.
Until now, the production of anti-bat ultrasound was thought to be quite rare in moths. It has been recorded in tiger moths, hawkmoths, and a single geometric moth species. However, the results of a decade-long moth survey that involved the collection and study of thousands of moths in Ecuador, French Guiana, Mozambique and Borneo in Malaysia have now revealed that such auditory defense mechanisms are much more common than previously thought. In fact, the night can be filled with so much chatter from bats and moths, it would be quite overwhelming if we could hear any of it.
“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,” said study lead author Akito Kawahara, curator at the McGuire Center for Lepidoptera and Biodiversity. from the Florida Museum of Natural History.
The findings of the study, published in the Proceedings of the National Academy of Sciences, identified no less than three new types of sound-producing organs in moths and added eight new subfamilies and potentially thousands of species to the list of moths using ultrasonic signals. The authors estimate that about 20% of moth species use ultrasonic signals to defend themselves against becoming fodder for bats.
Ultrasonic emissions are so successful in thwarting bat attacks that they have evolved independently many times in moths. In each case, the moths modified a different part of the body to become a finely tuned ultrasonic instrument.
“Tiger butterflies have structures called tymbals, which twist inward and outward,” Kawahara said. “Some of them [the moth species] use structures on their wings, some use their abdomens, while others use modified genitals!
The authors describe several of the newly identified clickers and scrapers that moths use to produce bat-repelling ultrasound. This includes a species of calpin butterfly that rubs overlapping abdominal scales, similar to how crickets emit their characteristic chirps. Another species, in a group called the snout moths, makes noise by using a guitar pick-like structure between its wings, which is scraped when the moth is in flight.
The researchers undertook a final two-week project in Ecuador, where they recorded the alarm calls of every moth 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 results showed that not all moth species compose their own ultrasonic melodies; instead, they tend to copy the calls of other species, especially those that are poisonous or bad for bats. Some moths are not good for food, and they warn bats not to waste their time, by emitting ultrasonic calls when they detect a bat. Bats quickly associate these warning calls with noxious-tasting moths and don’t bother to catch them. The researchers propose that a surprising number of non-poisonous butterfly species have developed acoustic mimicry and protect themselves by calling, just as poisonous species do.
The study’s lead author, Jesse Barber, is a professor of biology at Boise State University. He said more work is needed to uncover the exact nature of these sounds, but he suspects that the pioneer moths at the center of these rings of acoustic mimicry are likely harmful, while the mimics at the periphery are only fake advertisers.
“Moths and butterflies are collectively one of the most diverse groups on the planet, containing one in 10 named animals. If these results come to fruition, it will likely be the largest collection of mimicry complexes on Earth,” noted Professor Barber.
Anti-bat signaling is not limited to moths. Some tiger beetles can also create defensive clicks on bats by flapping their wings against their protective coverings. Other groups of insects, such as grasshoppers, crickets and mantises can hear incoming bats, and Barber notes the possibility that some have the yet unknown ability to communicate with their pursuers. But with around 40% of insect species currently facing extinction, at a rate that eclipses researchers’ ability to discover and name them, he warns of the very real possibility that this ultrasonic symphony will die down before we had a chance. to hear it or learn what it means.
“These mimicry complexes are probably not limited to moths,” Professor Barber said. “The whole tapestry of insect nightlife is probably involved, but the chance to understand the natural world is slipping away. So many lineages are disappearing that we’re probably in the last golden age of biology. We can still understand how life went, if we do it now.
By Alison Bosman, Terre.com Personal editor