Many species of moths, which are the favorite prey of many bats have developed all sorts of tricks to avoid prey. Some have developed a sense of hearing at the appropriate frequencies and others, unable to hear, have developed voice camouflage solutions instead of a visual one.
MYou: Thomas NeilPostdoctoral Fellow in Biological Sciences, University of Bristol
There are not many better examples of two species involved in an intense struggle for survival than bats and moths. These two animals are the archetype of an evolutionary arms race, with each attempting to overshadow the other in the battle between predator and prey.
Bats first developed the ability to resonate about 65 million years ago. By producing high-frequency “clicks” with their mouth or nose and listening to echoes as they return from objects, bats are able to “illuminate” the world around them through sound.
This feature is called Ecolocation or Ecolocation and it allows bats to take advantage of hunting opportunities that are not available to other flying predators. Because of the lack of reliance on light they have the opportunity to chase and hunt nocturnal insects.
This ability put tremendous pressure on the insects that became the hunting of bats such as crickets, winged moths and grasshoppers. Many of these insects have developed an unusual variety of counter-adaptations to help them survive, but in no species are there such obvious adaptations as in moths.
Many moths have developed sensitive ears to echo calls from bats. The ears allow them to hear bats approaching and take evasive action, such as hiding in the foliage or flying away.
Some moths have even evolved and produce their own sounds, alerting bats that they are poisonous. If a species emits high-frequency clicks similar to that of an attacking bat, the bat will quickly learn to associate the sounds of the moth with bad taste and stop focusing on them completely.
The clicks of some species of moths are even capable of “mimicking” the acoustic cries of bats. By scheduling their clicks to coincide with the clicks of an approaching bat, the moths are able to confuse the bat, making it difficult for it to reach its destination.
Collects sound
My colleague The University of Bristol and I are most interested in the protections of moths that have no ears. If they can not hear a bat approaching, how might they increase their chances of survival? Moths without ears had to develop passive defenses, i.e. adjustments that existed all the time, whether the moth was under threat from a nearby bat or not.
Recently, we unveiled two such matches in a mini moth without ears. The first is acoustic camouflage. This is the equivalent of visual camouflage that we see when an octopus blends in perfectly with a rock that is in the background, or that an insect looks just like a leaf.
Antheraea pernyi, a species of moth without ears, has developed sound-absorbing wings that are used for acoustic camouflage. The author provided
To achieve this, mothless moths have developed special scales on their wings and body that absorb the sound energy from the reverberation of the bat, causing the bat to receive a reduced echo from the body of the moth. By muffling the sound in this way, the moth is literally able to disappear from the “landscape” of the bat in the night sky.
The way these scales are able to absorb sound is quite spectacular. Each spot on the moth wing vibrates in response to sound waves, but each such area vibrates at slightly different frequencies. Working together, moths are able to absorb sound at all frequencies that bats use for hunting, ranging from 11 kHz to 212 kHz.
By vibration, the scales dissipate the sound energy by converting it to kinetic energy and heat. We hope the lessons we have learned from these scales will help us create thinner sound-absorbing materials to line the walls of buildings like music studios and buildings on busy residential roads, making the world a quieter place for everyone.
Diversion attacks
Another adaptation we have identified in trees is acoustic bait. This is the analogy to eye spots in fish and butterflies. The idea is to divert the predator attack from the vital body parts of an animal, such as their head, towards parts like fins and wings that can be lost without fatal damage.
In moths, these baits take the form of elongated and twisted structures on the tips of the wings. Some moths also have a long rear end that ends similarly, known as Streamer lures.
Examples of streamer baits in two different moth species. Courtesy of the author
The unique, wavy shape of these structures means that these body parts are excellent in sound reflection, as well as its scattering at many different angles. Our research has shown that bats will attack these streamers and not the vulnerable body of the moth itself. Thus the moth will increase the chance of surviving bat attacks and live another day.
When we uncover such fascinating new tricks, we are probably just beginning to understand all the adaptations that these species have developed. There is already some evidence that bats have changed their echo calls to deceive insects that have ears, while it remains to be seen if they can overcome other forms of protection such as acoustic camouflage. The moths seem to be at the top right now in this arms race, but the bats probably have a few more tricks on their wings to fight them off.
For an article in The Conversation
More on the subject on the Knowledge website: