They announce: “Don’t eat me – I’m inedible!”, or they make confusing noises: A surprising number of moth species produce ultrasonic sounds to ward off bats, researchers report. Interestingly, some deliberately announce untruths: They imitate the sounds of their toxic relatives – but are actually non-toxic. It is apparently a widespread form of so-called mimicry, say the scientists.
To avoid the hungry eyes of predators, certain butterflies once hid their activity under cover of darkness. But the moths were not safe there for long: bats followed them into the darkness and pursued them with their sophisticated biosonar. The hunters of the night emit high-frequency screams that are reflected by the insects’ bodies. The fine echoes enable them to precisely locate their prey and snatch it directly from the air. But the moths did not remain helpless victims – they armed themselves with their enemies in the course of their common evolution. Researchers have already uncovered different strategies.
On the trail of noisy moths
For example, some species react to the sounds of bats with clever evasive maneuvers, and others have created sound-absorbing structures to camouflage themselves acoustically. It was also already known that some moths emit their own ultrasonic signals. As a result, some species apparently wrap themselves in a cloak of sonar-interfering noise, making it difficult for them to detect bats with their echolocation. However, the sounds can also serve as a deterrent: the insects alert the bats to their toxicity or their bad taste. This acoustic threat corresponds to the function of the colorful warning colors of some species of butterflies.
So far, however, acoustic defense mechanisms in moths have only been known from relatively few examples. The researchers led by Akito Kawahara from the Florida Museum of Natural History have therefore investigated how widespread these processes actually are. Their results are based on extensive studies of moth species in different regions of the world. To determine whether they produce ultrasounds in response to a bat attack, the scientists simulated attacks by physically harassing the insects or playing them ultrasonic sounds made by bats. They also examined the mechanisms of sound production and the extent to which the “loud” moth species are inedible.
Widespread and sophisticated
It turned out that acoustic defense mechanisms are much more common than previously thought. “There are masses of moths that produce ultrasonic sounds that we know very little about,” says Kawahara. Based on their findings, the researchers estimate that about 20 percent of all moth species produce anti-bat sounds. Information on the history of evolution shows that sonar disruption methods and warning tones of inedibility have been developed independently in various moth lineages. The second concept is more widespread, according to the results.
During their investigations, the researchers also discovered previously unknown methods of noise development in moths. In one species, they discovered overlapping ventral scales that produce sounds when rubbed, similar to how crickets produce their distinctive chirping. Another species produces ultrasonic sounds via special structures in the wings, which are made to sound when flapping in flight, the team reports.
Acoustic mimicry
The results of the study also show that a concept familiar from butterflies and other insect species is widespread in moths in an acoustic form: mimicry. Harmless diurnal insects take advantage of the off-putting colors or markings of dangerous, poisonous, or bad-tasting species by mimicking their appearance. This allows them to dispense with the production of the deterrent substances. In the case of moths, something similar is now emerging.
The research shows that many moth species that are actually tasty mimic the sounds of poisonous or inedible species in order to benefit from their deterrent strategy. So they only fool the bats into not being good prey. “Moths and butterflies collectively are one of the most diverse groups on the planet. If our results are confirmed, then we are dealing with an extremely widespread form of mimicry,” says Kawahara.
Source: Florida Museum of Natural History, Article: PNAS, doi: 10.1073/pnas.2117485119