The summer heat is about to dissipate, but do you still not know who sings the familiar "background music" of summer?

Although the dog days are over, summer in Chongqing seems to have just reached its climax. As soon as you go out, you will see familiar faces everywhere.

Chongqing is a mountainous city, and every summer it has its own "background music" that plays in a loop - the chirping of cicadas. Some people can appreciate the chirping of cicadas, while others are quite impatient with these constant chirping creatures. Even when the middle school entrance examination and the college entrance examination are approaching, there are often news reports of parents going to great lengths to catch cicadas.

01 Why do cicadas keep chirping?

The reason why cicadas chirp is certainly not to disturb human study life. In fact, they have no interest in things like exams. Like most insects that chirp, their loud "singing" basically has only one purpose: to seek a mate.

After all, these little guys, although their lives are very long by insect standards, only live for a few weeks to a few months after they emerge and have the ability to fly. Insects with shorter lifespans than them, such as various mayflies, tend to appear in dense clusters when they emerge, and they don't have the problem of "not being able to find a partner". But cicadas are usually distributed in much smaller densities, so it is really difficult for them to find a mate without actively making sounds.

In addition, cicadas will chirp when they are suddenly captured by natural enemies or when they are trying to call their companions hiding nearby.

Image source: Pixabay

The calls of different cicadas are also quite different, which can help the opposite sex of the same species to accurately find the target and avoid "matching couples at random". For example, the cicada (a medium-sized cicada, commonly known as "cicada"), which is famous for Zhuangzi's saying "Morning mushrooms do not know the new moon and full moon, and cicadas do not know spring and autumn", has a unique and loud call. Other types of cicadas, such as various bear cicadas and winter cicadas, have "eighteen kinds of timbres" that are either sharp or low, in order to highlight their own characteristics as much as possible.

02 How do cicadas make sounds?

Although people are accustomed to calling the chirping of cicadas "singing", these insects naturally do not have a "throat" in the physical sense: anyone who has caught a cicada will notice that they have a "mouth" similar to a straw, which is called a piercing-sucking mouthpart.

As an insect that feeds directly on liquid food, cicadas will directly insert these "straws" into the blood vessels of trees to absorb juice from them. This eating habit makes them always store a large amount of water in their bodies, and also makes it easy for many people who try to catch them to urinate on their hands.

Since cicadas do not have human vocal cords and mouths, they naturally cannot "sing" directly. The equipment they use to make sounds has two "mosts" among insects: the loudest volume (often reaching 80 decibels) and the most complex.

Generally speaking, cicadas, or more precisely, male cicadas that need to court, have a tympanic cavity as their main organ of pronunciation. This organ is a cavity located in the abdomen, and its main components include the dorsal valve, ventral valve, tympanic membrane, pronunciation muscles (tympanic muscles), tendon discs, tendon protrusions, ventral adjustment muscles, mirror membranes, pleated membranes (folded membranes), third valves, resonance chambers (air chambers), etc. It vibrates the tympanic membrane by contracting the pronunciation muscles (tympanic muscles) at a high frequency, and then vibrates the air in the tympanic cavity to make sounds. Some cicadas also have secondary organs of pronunciation, which are accessory organs used to rub against the wings to assist in pronunciation.

03 The real "underground worker"

After successfully attracting females with their "singing", cicadas will mate for tens of minutes to hours, after which the female cicadas will lay eggs on the branches at the appropriate time. As the branches dry up and fall off, in the autumn and winter of the year or the beginning of spring of the following year, the cicada larvae will hatch and burrow into the ground to begin their long "underground work".

As an insect with incomplete metamorphosis, the larvae of cicadas have a similar structure to adults, except that they have no wings and their forelimbs are stronger, allowing them to dig tunnels underground.

Like adults, cicada larvae also feed on plant sap (of course, sap from the root system) and spend a long time underground. After a series of metamorphosis and growth, they will eventually accumulate enough energy for metamorphosis, and leave the caves in the summer or autumn, climb up the trees, and begin the "highlight moment" of their lives.

The length of time spent underground varies for different cicadas, and can be 2, 3, 5, 7, 11, 13 years, or even 17 years! However, generally speaking, this period of time is a prime number, which ensures that there will not be too many cicadas rushing out in the same year, causing too much pressure on the environment and causing meaningless "involution".

In addition, cicadas with a longer larval stage, such as the 17-year cicada, mainly live in North America, which is likely related to the large-scale glacial activity that often occurred in North America during the Pleistocene: due to the lack of large east-west mountain ranges on the continental terrain, it is impossible to resist the glaciers and cold air currents from the north to the south, and "years without summer" may often occur. Those cicadas that can wait longer in the warm underground are naturally more likely to survive. Therefore, after a series of natural selection, the cicadas in North America have an extra-long "endurance" and eventually evolved into a species that can persist underground for more than ten years.

04 The symbolic meaning of cicada

In traditional culture, especially in Asian traditional culture, cicadas have many meanings, among which "purity and non-materialism" is the most common one. After all, this is a real insect that "feeds on wind and drinks dew".

In addition, the short life span of cicadas also makes them a symbol of "impermanence". In late autumn, the collective death of a large number of cicadas easily reminds people of cycles and reincarnation... This made early Buddhism and Taoism like to use cicadas as a metaphor.

In addition, cicadas are often used to represent "resurrection and rebirth" or "silent devotion", largely because people can observe the larvae of cicadas living underground and the process of the larvae transforming into pupae.

Image source: Pixabay

The image of "cicada shedding its shell" is often used in Taoist myths and legends to describe the old body discarded by those who have "attained the Tao". After all, the process of transforming from a small insect underground into a cicada with wings that soars into the sky is too similar to the logic of "transcendence into heaven" in ancient legends.

Of course, cicadas cannot understand or care about all the observations, comments, and implications given by humans. These insects, which have existed for thousands of years, will continue their life cycle for a long time to come, emerging from their wings and singing again and again, and integrating themselves into the material cycle of nature.

For them, being able to complete a life cycle safely is the whole meaning of their existence. As for how their singing is appreciated, what does it matter?

Source: Chongqing Science and Technology Museum

Author: Suo Hefu, a popular science fiction writer, won the Silver Award for Novella in the China Science Fiction Nebula Award

Audit expert: Li Chunli

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