This year, the eastern United States will usher in a super explosion of cicadas, and it is estimated that trillions of cicadas will be unearthed en masse in a short period of time. Many media reported that this is a rare spectacle that occurs once in 200 years, and as soon as the news came out, a large number of Shandong people who love to eat exploded in the comment area:
So what is so special about the cicadas that are about to sweep the United States this time? Can they be fried and eaten? In addition, why do they break out again every once in a while? Today we will talk about it together~
This time the cicada that has attracted attention in the United States,
What's the difference, exactly?
Generally speaking, the lifespan of a cicada is two to five years. They lay eggs on the branches, and the newborn nymphs burrow into the ground to eat the sap from the roots. Some will come out in two years and reproduce, while others will wait three or four years or more. However, every year a new batch of cicadas is unearthed, so you can hear the cicadas chirping every year.
Freshly fledged cicadas
However, there are several special cicadas in North America, which are different from ordinary cicadas, and they are collectively called "periodic cicadas", which are the cicadas that have attracted attention in the United States this time. It differs in two main ways:
First, they spend a very long time in the field, some 13 years, some 17 years.
Second, they are not unearthed randomly, but in groups, and there are many of them at one time. For example, a city may have a cyclical cicada outbreak this year, then there will be no next year, and there will be no next year, and it will take 17 years for the next outbreak to occur.
However, there is not necessarily synchronization between different regions, so in most years in North America, there are periodic cicadas, but each time they only erupt in a certain range, some years have a large range, and some years have a small range. The annual cycle of cicadas will be concentrated in 1~2 weeks to emerge, and they can live for less than a month after being unearthed, so each outbreak does not exceed one and a half months.
Because of the clustering nature of periodic cicadas, outbreaks are often particularly severe and overwhelming. Of course, there are also some places where the cicadas are in recession, and they can't see anything when it comes to the cycle.
Two of the historically recorded periodic cicada colonies have now disappeared, and some of the cycles that should theoretically have existed have never been observed in reality, either because they were extremely hidden or became extinct much earlier. The seventeen-year-old cicada should theoretically have 17 nests, but in reality there are only 12 nests, and the thirteen-year-old cicada should theoretically have 13 nests, but in reality there are only 3 nests left.
By the way, the synchronization of periodic cicadas is also not perfect, and there are always individual cicadas who will remember the time incorrectly. Interestingly, the most common mistake of the 17-year-old cicada is 4 years earlier, while the most common mistake of the 13-year-old cicada is to delay it by 4 years.
周期蝉。 图片来源：University of Connecticut
Why do periodic cicadas like to appear in groups?
The most classic theory is that this is to effectively avoid predation. Cicadas are not poisonous, do not have spikes, do not fly fast, and have little resistance to predators. Other insects can hide for a while, but the cicada relies on its call to attract the other half, and anyone can hear it.
Then there is only one strategy left, which is to overwhelm the predators by numbers: as long as I have enough births, you will not be able to eat them all.
But this strategy is not to blindly pursue numbers, because predators can also live. Imagine that you gave birth to 10,000 of them this time and were eaten by a hundred birds. The next time, 20,000 were born at the expense of blood, and the number of other birds also increased to 200, so it will not be over.
So the key to this strategy is actually to create a huge fluctuation in the quantity, which is usually small and suddenly increases at critical moments. In this way, the number of predators cannot go up on weekdays, and they cannot be eaten at critical moments. At this point, cicadas have a great innate advantage, because cicadas spend most of their lives in the soil, and predators can't reach them.
This plan should be said to be very successful, and anyone who has been quarreled with by cicadas in the summer understands it. It's not perfect, though. Some predators, such as arthropods, can sleep or die after the season passes. Other predators, such as birds, do not have a constant need for food, and can make effective use of cicada resources as long as they choose to brood during the cicada season. In conclusion, predators have a certain ability to keep up with fluctuations.
If you want to improve the scheme further, you need to make it harder to keep up with the fluctuations in numbers. A common way of thinking is to create fluctuations not only from season to season, but also from year to year. The birds that are full in the big year starve to death in the small year, and there will not be so many birds to eat the cicadas in the next big year. There are some fruit trees that use this version 2.0 scheme, alternating the size of the year.
However, there are very few predators in nature that specialize in eating one type of prey. What if the predator found another source of food when he was young, and what if another prey was the opposite of you?
Version 3.0 of the solution to this problem has emerged: extend the cycle. A once-in-a-decade year is far safer than a biennial year. In fact, humans have discovered a four-year cycle of cicadas in India, commonly known as the World Cup cicada, because the outbreak year coincides with the World Cup.
Even this solution still has one final weakness, which is that it is collided with other cycles by coincidence. If a cicada's cycle is 12 years, then other predators with periods 2, 3, 4, and 6 will be able to coincide with it on time. Here the advantage of prime numbers (13 and 17 are relatively large primes) finally appears: it has a factor of only 1 and itself, which minimizes the probability of overlapping with other periods. Version 4.0 not only synchronizes the cicadas with the new year, each year is separated by a long time, but also the cycle is prime.
This explanation is the most classic, but it is only one of them. Another explanation, which has gradually become more popular in recent years, is that this strategy prevents hybridization between different nests. Of course, these explanations are not contradictory, but complement and reinforce each other.
The new explanation suggests that the original origin of ultra-long life cycles was more important than just escaping predators, such as accumulating nutrients in harsh environments, and that the North American cyclic cicada may have originated when the glacier was just receding.
Most cicadas have a short life cycle, so genetically ultra-long-term cicadas are actually difficult to maintain, and they are easily diluted by the genes of ordinary cicadas. Some of the cicadas that have mistimed may be the product of dilution. Therefore, the species with a large prime number cycle are left behind, and each time they are unearthed, they are faced with a different group of cicadas, and it is not easy to be repeatedly infiltrated by the same group of foreign genes to change the cycle.
A two-nest year for any two flocks of cyclic cicadas is now a rare event that occurs once in 221 years, and it is the result of this choice.
A major outbreak once in 200 years,
What's going on?
As mentioned earlier, the seventeen-year-old cicada should theoretically have 17 nests, but now there are only 12 nests, and the thirteen-year-old cicada should theoretically have 13 nests, but in fact there are only 3 nests left.
This is a map of the USDA Forestry Service, showing the location of periodic cicada nests in the U.S. on a county-by-county basis, and when they will next appear
The inside of the 17-year-old cicada and the inside of the 13-year-old cicada do not collide with the schedule - in fact, if they do, they will continue to collide, and they will be classified as the same nest. But there will be a collision between the 17-year-old cicada and the 13-year-old cicada. 17 and 13 are both prime numbers, and the least common multiple is 221 multiplied by the two, so any two nests colliding is a once-in-221 occurrence. 2024 is such a two-nest year.
The twin nest year is not as powerful as it sounds, after all, there are many nests. Even if many of the nests have disappeared, there are 36 combinations of existing nests, which are not uncommon to occur once in six years on average. But we're in the middle of a "famine year" where the last time it happened was in 2015, and the next time it's 2037.
However, 2024 is a very strong year for all 36 twin nests, mainly because of the size of this wave of nests. The 13-year-old cicada is ranked in the nineteenth nest, which is particularly widely distributed, and is almost the first among all periodic cicadas in terms of area. The 17-year-old cicada is ranked as the thirteenth nest, which is known for its large numbers, although it has a relatively narrow range. "Two strong nests serve the same year", and "blessing" is naturally not small.
In addition, there is another thing that is of interest to biologists this year. The periodic cicada is not a single species, but a total of seven species, and the same nest cicada often includes several different species. In 2024, the year of the twin nests, all seven species will be present. This in itself is not very unusual, but it is interesting and scientifically beneficial to occur alongside the simultaneous eruption of two nests.
However, nests 19 and 13 do not coincide in much of the same range, except in a narrow strip of Illinois. Because this is the fringe area of the two nests, there are probably no super scary double cicada disasters, but scientists can take the opportunity to observe whether there is hybridization or other interaction between the two nests.
Do you need to worry about a twin nest year?
Let's start with the answer: don't worry too much.
First of all, all the 13- and 17-year-old cicadas live in North America (mainly the United States, with a very small distribution in Canada), and those who live elsewhere certainly don't have to worry.
The number of periodic cicadas at the outbreak site is extremely large, and the cries are noisy and annoying, but that's about it. The periodic cicada is not poisonous and will not bite, in fact, it can be eaten, it is recommended to catch the monkey in the early morning (boil it as soon as possible after catching it, otherwise it will molt). The taste is not good after molting, the males have almost no meat, and the females are too dry and hard.
The empty shell of the cicada. The stock copyright picture, reprinting and using may cause copyright disputes
Periodic cicada outbreaks will have a certain impact on the local ecology, but not very much. Cicadas do not bite the leaves and only suck the sap, which causes the tree to grow slower but is almost not lethal. When laying eggs, the female cicada will cut a small section of bark, and if the eggs are too concentrated, it will occasionally cause serious damage to the young tree. In addition, during the outbreak, predators are too busy eating cicadas to other food, so other predators such as caterpillars will also cause more damage to the tree during this period.
Another interesting point is that periodic cicadas interfere with the tree's cycle. Oak trees are also typical creatures of large and small years, producing large waves of acorns in batches every two or three years to drown out predators. When the cyclical cicada erupts, a large number of cicadas sucking up sap will destroy the oak tree's nutrient reserves, so usually the oak tree's timer will be reset by the cyclic cicada, and no matter how many years are counted before, it will go through two small years after the outbreak.
Planning and production
Author丨Fan Gang, popular science creator