Big fangs, strong jaws, speed, incredible eyesight and much more are features used by predators of all breeds and stripes in the process of hunting. The prey, in turn, also does not want to sit idly by (wings, hooves, flippers, etc.) and comes up with more and more new ways to avoid unwanted close contact with the predator's digestive system. Someone becomes a master of camouflage, someone is smeared with poison, and someone throws their insides in the face of the offender (hello sea cucumbers). But there are those whose defense mechanism is not visible or even audible to us. Moths are a favorite food of bats. For many millions of years, both of them have been polishing their skills in ultrasound. Mice use it to find prey, and moths use it to detect predators. But "forewarned is forearmed" is not enough for moths, so they have developed the ability to create "radio interference" that disrupts the ultrasonic "vision" of bats. How do they do it, given their 100% deafness, and how effectively does it help them avoid death? We will look for answers in the report of the research group. Go.
Research basis
When hunting at night, you need to have either very good eyesight, or a keen sense of smell, or excellent hearing. Bats chose the latter, in a sense. The use of echolocation is very beneficial for bats. First, hunting at night limits the number of potential dangers and competition for food. Secondly, there are a lot of insects at night, that is, the chances of eating after 18:00 are much higher.
Bats produce ultrasound at different frequency ranges depending on the species. Moreover, even in one species, the frequency changes over time: at the beginning 130-150 kHz, and then 30-40 kHz.
While hunting, bats "emit" ultrasonic waves that "crash" into objects around it, including possible prey. The reflected waves are caught by the bat and it can maneuver among obstacles or precisely focus the attack on prey.
When evolution distributed talents, moths also did not stand aside. They are capable of producing ultrasonic noise or false signals that convince the bat that they are inedible. Some types of moths use stridulation. This unusual term is very easy to explain: remember how crickets βsingβ in the summer? This is what stridulation is. Another bright, or rather sonorous master of this talent, are cicadas.
An alternative source of sounds in moths can be percussion "castanets" - modified genital structures (yes, scientists called the genitals that produce sound, castanets; did you think people of science lack creativity?).
However, most species of moths use timbales (not to be confused with cymbals) - special cuticle formations on the surface of the body with an air "cushion" under the bottom.
In the study under consideration today, scientists paid attention to the genus of moths Yponomeuta, in which most species (and there are about a hundred of them) have an unusual formation in their arsenal - a translucent area on the wings without scales between the Cu1b veins
and Cu2. Scientists have found that this area is adjacent to a number of ridges, which may indicate the involvement of this area in sound production through stridulation (possibly).
In the image on the left (A), the area of ββa translucent mass is circled in white, and on the image on the right (B), SEM images of the same area.
Scientists set themselves the task of answering a number of questions: does this translucent area produce sound or not, what are its acoustic properties (if it does), and how these sounds are used by the moth in his life.
The main subjects who were supposed to help find answers to the above questions were individuals of two species of moths - Y. evonymella and Y. cagnagella.
Find 10 differences: Y. evonymella (left) and Y. cagnagella (right).
The subjects were taken from the wild while still in the larval stage. The resulting pupae were kept in special containers 297 x 159 x 102 mm at a temperature of 21Β°C.
Observation results
The scientists recorded free and fixed flights of the subjects: 15 free and 2 fixed flights of Y. evonymella; 9 fixed flights of Y. cagnagella. During flight, the moths produced the same ultrasonic clicks during each wing beat (plots below).
Spectrogram of ultrasonic clicks during a single flap of a moth's wings.
The spectrogram above shows multi-colored areas. The first (red) is the frequency range of sounds produced by moths of the subfamily Arctiinae against bats. And the second (blue) is the auditory range of Eptesicus fuscus bats.
In total, two ultrasonic pulses were recorded during the stroke: one at the beginning of the stroke and the second at the end of the stroke. It was during the first pulse that the frequency of clicks was greater. The number of clicks per pulse, judging by the observations, coincides with the number of bands in the semitransparent area. In Y. evonymella, the average value of clicks per 1 ultrasonic pulse is 12.6 Β± 1.7, and they have 11 bands in the translucent area (pay attention to the numbering on the SEM image of the wing).
Next, the scientists removed the tymbals (area of ββ260 x 800 Β΅m) from 12 Y. evonymella and recorded their flight sounds before and after the removal. The number of clicks per 100 ms period was also calculated, which is the equivalent of about 3 wing beats.
Seven individuals produced no clicks after removal, eight produced only 1 click, and four produced clicks, but in a smaller number and with a lower amplitude. As it turned out, in this four, the timbale areas (translucent areas) were not completely removed, therefore they were excluded from further analysis.
Empirically, scientists have confirmed that moths of both test species produce sounds. Now they decided to test them by ear (20 Y. evonymella and 4 Y. cagnagella).
The scientists reproduced the ultrasound while the subjects flew freely in the test room. Not a single individual reacted to this. The experiment was repeated, but dividing the individuals by species into separate containers, where they were at rest. Again, no one even flinched.
At the same time, by placing 10 individuals of Y. evonymella in one flight chamber, the scientists saw the reaction of the subjects to each other. And it was the same as in previous tests, that is, none.
What about stridulation? The scientists tested whether there were any signs of rubbing of any body parts to produce sounds in the test moths. And as it turned out, there are none. Notice the movements of the moth's wings during controlled flight in the video below.
In this video, we can see what changes occur in the position of the wings and their parts during the stroke.
With the translucent area under study, no friction was observed in other parts of the moth's body at any of the moments of the stroke. But clicks somehow appear. And this happens through the rotation of the hind wing along its axis from the base to the tip during the upper and lower phases of the wing stroke.
A detailed examination of this process showed that during supination (rotational movement of the limb) at the beginning of the stroke, the anal and jugal sections of the wing fold down relative to its anterior part along the claval furrow.
Flight of a moth, side view.
This process runs from the top to the bottom of the wing, so the translucent area is also involved. During this, ultrasonic clicks occur.
The table above shows the results of the analysis of ten clicks recorded in the transverse direction (90Β°) in all subjects (14 Y. evonymella and 9 Y. cagnagella). Spectral parameters, duration and amplitude of clicks were set.
In addition, an analysis was made of clicks (5 for each of 8 individuals) of horizontal orientation (0Β°, 45Β°, 90Β° and 180Β°).
The average value of the sound level of eight Y. evonymella subjects recorded from four directions: 0 Β° - microphone in front of the moth, 45 Β° - front side, 90 Β° - side, 180 Β° - behind.
No special differences were found: 0Β° and 45Β°, Z = 0,3, p = 1,0; 0Β° and 180Β°, Z = -2,3, p = 0,13; 45Β° and 180Β°, Z = -2,4, p = 0,11.
The scientists also calculated at what distance the bats will hear the clicks of moths, depending on the position. The results are as follows: 6.0 Β± 0.4 m at 0Β°, 6.5 Β± 0.4 m at 45Β°, 7.9 Β± 0.7 m at 90Β°, and 5.6 Β± 0.4 m at 180Β°. These indicators are displayed in the form of a diagram above (Π).
And here on the chart Π we see the amplitude of the reflected sound, which varies in the range of -35 ... -43 dB at frequencies in the range of 20 ... 160 kHz.
For a more detailed study of the study, I strongly recommend that you look at .
Finale
Evolution can be unprincipled, merciless, strange and even ironic, as the example of the studied moths shows. While completely deaf, these creatures are not without a "voice". Using translucent patches on their wings as they flap, the moths produce ultrasonic clicks that confuse hungry bats.
Such an unusual adaptation is a fact, but it will give rise to many more debates on how it was formed, what evolutionary changes the moths went through to develop such a mechanism, and how it all began.
We once again received confirmation that the world is full of amazing creatures that never cease to amaze with their talents, which we had no idea about.
And, of course, offtopic Fridays:
Here, everyone who suffers from mottephobia (fear of moths) must have had a heart attack of horror.
Thanks for watching, stay curious and have a great weekend everyone.
Thank you for staying with us. Do you like our articles? Want to see more interesting content? Support us by placing an order or recommending to friends, 30% discount for Habr users on a unique analogue of entry-level servers, which was invented by us for you: (available with RAID1 and RAID10, up to 24 cores and up to 40GB DDR4).
VPS (KVM) E5-2650 v4 (6 Cores) 10GB DDR4 240GB SSD 1Gbps free until spring when paying for a period of six months, you can order .
Dell R730xd 2 times cheaper? Only here in the Netherlands and USA! Read about
Source: habr.com