Once in 200 years, the United States will usher in a "big cicada plague"? Netizens: Fried food is so delicious

This year, the eastern United States will see a huge outbreak of cicadas. It is estimated that more than one trillion cicadas will emerge in a short period of time. Many media reported that this is a rare spectacle that only occurs once every 200 years. As soon as the news came out, a large number of Shandong people who love food exploded in the comment section:

So what is so special about the cicadas that are about to sweep across the United States? Can they be fried and eaten? In addition, why do they break out again after a period of time? Let's talk about it together today~

What is so different about the cicadas that have attracted attention in the United States this time ?

Generally speaking, a cicada's life span is two to five years. They lay eggs on tree branches, and the newly born nymphs burrow underground to eat the sap of tree roots. Some will come out after two years to reproduce again, while others will wait three or four years or even longer. However, a new batch of cicadas emerges every year, so you can hear the cicadas chirping every year.

Newly emerged cicada

However, there are several special cicadas in North America that are different from ordinary cicadas. They are collectively called "periodic cicadas", which are the cicadas that have attracted attention in the United States this time. There are two main differences between them:

First, they stay in the fields for a very long time, some for 13 years and some for 17 years.

Second, they are not unearthed randomly, but in clusters, with a large number of them at one time. For example, a city may experience an outbreak of periodic cicadas this year, but there will be no more next year, or the year after that, and it will take 17 years for the next outbreak to occur.

However, the emergence of periodic cicadas in different regions is not necessarily synchronized, so North America actually has periodic cicadas in most years, but each outbreak is limited to a certain range, with a large range in some years and a small range in others. Periodic cicadas emerge from the ground within 1 to 2 weeks each year, and can live for less than a month after emerging from the ground, so each outbreak lasts no more than a month and a half.

Because periodic cicadas gather in groups, outbreaks are often very severe and overwhelming. Of course, there are also places where cicadas are in decline, and when the cycle comes, nothing can be seen.

Two nests of periodic cicadas that were recorded in history have now disappeared, and some cycles that should have existed in theory have never been observed in reality, perhaps because they are extremely hidden or have become extinct long ago. Theoretically, there should be 17 nests of seventeen-year cicadas, but in fact there are only 12 nests now; theoretically, there should be 13 nests of thirteen-year cicadas, but in fact there are only 3 nests left now.

By the way, the synchronization of periodical cicadas is not perfect, and there are always individual cicadas that get the time wrong. Interestingly, the most common error for 17-year cicadas is 4 years early, while the most common error for 13-year cicadas is 4 years late.

Periodical cicada. Image credit: University of Connecticut

Why do periodic cicadas like to appear in groups?

The most classic theory is that this is to effectively avoid being preyed on . Cicadas are not poisonous, have no stings, and do not fly very fast, so they have basically no resistance to predators. Other insects can at least hide, but cicadas rely on their calls to attract their mates, and everyone can hear their calls.

That leaves only one strategy, which is to overwhelm predators with numbers: as long as I give birth to enough, you won’t be able to eat them all.

But this strategy is not just about pursuing quantity, because predators can also reproduce. Imagine that you gave birth to 10,000 birds this time, and they were eaten by 100 birds. Next time, you will give birth to 20,000 birds at all costs, and the birds will increase to 200. This will go on forever.

Therefore, the key to this strategy is to create huge fluctuations in numbers. The number is small at ordinary times, but suddenly increases at critical moments. In this way, the number of predators cannot increase on ordinary days, and they cannot eat all the predators at critical moments. Cicadas have a great innate advantage in this regard, because cicadas spend most of their lives in the soil, out of reach of predators. They suddenly emerge from the soil in the summer, catching predators off guard.

This solution is probably quite successful, and anyone who has been disturbed by the cicadas in the summer will understand it. However, it is not perfect. Some predators, such as arthropods, can hibernate or die after the season is over. Other predators, such as birds, do not have a constant demand for food. As long as they choose to raise chicks during the cicada season, they can effectively utilize cicada resources. In short, predators have a certain ability to keep up with fluctuations.

To further improve the scheme, we need to make the fluctuations in numbers more difficult to follow. A common idea is to create not only seasonal fluctuations, but also fluctuations between years. Birds that are full in the big year will starve to death in the small year, and then there will not be so many birds to eat cicadas in the next big year. Some fruit trees use this version 2.0 scheme, alternating between big and small years.

But in nature, few predators specialize in eating one type of prey. What if a predator finds another food source during a lean year? What if another prey has a lean year in the opposite direction?

The 3.0 version of the solution to this problem has emerged: extend the cycle. The New Year's Eve, which occurs once every ten years, is much safer than the New Year's Eve, which occurs once every two years. In fact, humans have discovered a cicada with a four-year cycle in India, commonly known as the World Cup cicada, because the outbreak year coincides with the World Cup.

Even this scheme still has a final weakness, which is that it may be hit by other cycles by coincidence. If a cicada has a cycle of 12 years, then other predators with cycles of 2, 3, 4, and 6 can overlap with it on time. Here the advantages of prime numbers (13 and 17 are both relatively large prime numbers) finally appear: its factors are only 1 and itself, which minimizes the probability of overlapping with other cycles. The 4.0 version of the scheme not only allows cicadas to synchronize the big year, but also each big year is separated by a long time, and the cycle is a prime number.

This explanation is the most classic, but it is only one of the explanations. In recent years, another explanation has gradually become more popular, that is, this strategy can prevent hybridization between different nests . Of course, these explanations are not contradictory, but complement and reinforce each other.

The new explanation suggests that when the extremely long life cycle first originated, it had a more important function besides escaping predators, such as accumulating nutrients in harsh environments. In fact, the periodic cicadas in North America may have originated when the glaciers had just retreated.

Most cicadas have a short life cycle, so it is difficult to maintain cicadas with a genetically long cycle, and they are easily diluted by the genes of ordinary cicadas. Some of the cicadas that got the timing wrong may be the product of dilution. Therefore, species with prime long cycles are selected to be left behind , and each time they emerge from the ground, they face a different group of cicadas, so it is not easy for the same group of foreign genes to repeatedly infiltrate and change their cycles.

Today, a double-nesting year between any two populations of periodical cicadas is a rare event that occurs once every 221 years, a result of this selection.

What is the cause of this once-in-200-years eruption ?

As mentioned earlier, theoretically, the seventeen-year cicadas should have 17 nests when fully loaded, but now there are actually only 12 nests; theoretically, the thirteen-year cicadas should have 13 nests when fully loaded, but now there are actually only 3 nests left.

This is a USDA Forest Service map showing, county by county, where periodic cicada nests are located in the U.S., and when they will next emerge.

The 17-year cicadas and the 13-year cicadas will not collide in their schedules. In fact, if they do, they will keep colliding and will be classified as the same nest. But the 17-year cicadas and the 13-year cicadas will collide. 17 and 13 are both prime numbers, and the lowest common multiple is 221 , so any collision between any two nests will only happen once every 221 years. 2024 is such a double nest year.

The double nest year is not as bad as it sounds, after all, there are a lot of nests. If periodical cicadas follow the theoretical schedule, then every year should be a double nest year; even if many nests have disappeared, there are 36 combinations of nests that exist, which is an average of once every six years, not very rare. However, we are currently in a "bad year". The last time this happened was in 2015, and the next time will be in 2037.

However, 2024 is a very powerful year among all 36 double nest years, mainly because of the large size of this wave of nests. The 2013 cicadas ranked in the 19th nest, which has a particularly wide distribution range and is almost the largest in terms of area among all periodic cicadas. The 2017 cicadas ranked in the 13th nest, which has a relatively narrow distribution range but is famous for its large number. "Two powerful nests serve in the same year", "blessing" is naturally not small.

In addition, there is another thing that happened this year that is mainly of interest to biologists. Periodical cicadas are not one species, but seven species in total, and the same nest of cicadas often includes several different species. In 2024, the year of the double nest, all seven species are present. This is not very rare in itself, but it is also very interesting and beneficial to scientific research when it occurs together with the simultaneous outbreak of two large nests.

However, the distribution ranges of the 19th and 13th nests are generally not overlapping, and only a narrow strip of Illinois can be seen at the same time. Because this is the edge of the two nests, there is probably no super-terrifying double cicada plague , but scientists can take the opportunity to observe whether there is hybridization or other interactions between the two nests.

Is there any need to worry if we encounter a double nest year?

Here’s the answer first: Don’t worry too much.

First of all, all 13-year and 17-year cicadas live in North America (mainly the United States, with a very small number distributed in Canada), so people living elsewhere certainly don't have to worry.

There are so many periodical cicadas in the outbreak area that they are noisy and annoying, but that's all. Periodical cicadas are not poisonous and don't bite people. In fact, they are edible . It is recommended to catch them in the early morning (and boil them as soon as possible after catching them or they will shed their skin). After molting, they are not tasty. The males have almost no meat, and the females are too dry and hard.

The empty shell of a cicada. Copyright image from the photo library. Reprinting and using it may cause copyright disputes.

Periodic cicada outbreaks have some impact on the local ecology, but not a big one. Cicadas do not bite leaves but only suck sap, which can slow down tree growth but rarely kill them. Female cicadas cut a small section of bark when laying eggs, and laying eggs too densely can occasionally cause serious damage to young trees. In addition, during an outbreak, predators are too busy eating cicadas to care about other foods, so other prey such as caterpillars can cause more damage to trees during this period.

Another interesting point is that periodical cicadas interfere with the tree cycle. Oak trees are also typical organisms with a large number of acorns produced every two or three years to overwhelm predators. When periodical cicadas burst, a large number of cicadas suck sap and destroy the nutrient reserves of oak trees. Therefore, the oak tree's timing is usually reset by periodical cicadas. No matter how many years have been counted before, they will experience two small years after the outbreak.

Planning and production

Author: Fang Gang, popular science creator

Reviewed by Lu Ping, Researcher at the Institute of Zoology, Chinese Academy of Sciences, Planned by Xu Lai

Editor: Yinuo

Proofreading: Xu Lai, Lin Lin