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Photo Source: Unsplash2 billion, 20 000 000 000 million 2 followed by 16 zeros: this is the (approximate) number of ants on earth.

If asked about the first insect they knew in childhood, most people's answer might be ants. There is no other reason-there are so many ants that they can be found in almost every corner of the land except the South Pole.

Edward Wilson (Edward Wilson), a famous biologist and "father of sociobiology", has a special preference for these small creatures. He calls ants and other invertebrates "little things that dominate the world" (the little things that run the world): "their numbers are staggering. If Homo sapiens hadn't accidentally appeared on the African grasslands as primates and migrated around the world, visitors from other galaxies would have been happy to call Earth 'Ant Planet' when visitors from other galaxies arrived (remember my words, they will come sooner or later)."

However, we know almost nothing about these "true masters of the earth". We can't even answer the most basic question-how many ants are there on earth?

"ants account for 2/3 of the total biomass of all insects. They have millions of species, and we know next to nothing about them." Edward Wilson (photo source: original paper) is not just a question of curiosity, it's not just about human curiosity. We all know that ants play an important role in ecosystems: they spread seeds, loosen the soil, and accelerate the decomposition of organic matter. And the fact that small ants can have such an important ecological status is closely related to their large number.

Therefore, how many ants there are has become a question that many ecologists have tried to answer. Wilson and ecologist Bert H ö lldobler have done some rough calculations: based on the density of insects in southeast England, they simply extrapolated the global insect population, and then assumed that the total number of ants accounted for about 1% of all insects, and finally came to the conclusion of 10% only and another conclusion you may have heard of: the biomass of ants (in dry weight). That is, the calculation of carbon mass) is about equal to the biomass of all mankind (the global population at that time was about 5 billion).

Photo source: Unsplash obviously, whether extrapolating the total number of insects in the world from a single region, or estimating that ants account for 1% of the total number of insects, such calculations are not accurate. We can also think about this from another perspective: if you want to estimate the number of students in a school, of course you can count the total number of students in the city, divided by the number of schools in the city, to get a rough result.

But there is another more accurate way-to count the number of students in each class in this school, and then add up the size of each class.

Recently, based on a similar approach, a team at the University of Hong Kong in China came up with a new ant census number: 2 × 10.

This number may be difficult to make people feel real, but we can look at it another way: on average, each person corresponds to 2.6 million ants, and the total biomass (dry weight) of ants is about 12 million tons, accounting for 20% of the total human biomass. It's about the weight of two pyramids of Khufu.

The study, published in Proceedings of the National Academy of Sciences (PNAS), is the first "bottom-up" method to estimate the total number of ants. According to the survey of ant density in different regions, the researchers estimated the average number of ants in different biota. The biota here refers to areas with similar climatic and geographical conditions, such as tropical rain forests, temperate grasslands, etc., just like different classes in a school. Add up the number of ants in each biota and you get the total number of ants in the world.

Biomass of different organisms (dry weight, unit: million tons) (picture source: original paper) these regional data are mostly found from the existing literature, and some of them are sampled by the research team themselves. When sifting through the previous literature to calculate the number of ants, the researchers especially chose the classical Winkler litter extraction method: take away the fallen leaves and topsoil in a specific area, and collect the insects in the litter by fully drying. This method can fully collect insects on the surface of a certain area, but there are also some problems. Because the collection is often carried out in a very short period of time during the day, the changes in the number of insects at different times are ignored. And this method does not apply in places where there is a lack of litter, such as open grass.

Therefore, as a supplement, the research team also chose another method: the trap method. This method only needs to set traps on the ground and collect ants that fall in within a certain period of time. Obviously, this method can not give the exact number of ants per unit area, but by comparison, we can judge the activity intensity of ants in different areas, and when combined with Winkler litter extraction method, we can calculate the number of ants in other areas.

Photo Source: Unsplash in this way, if we assume that the impact of ant species and ecological environment on the number of ants in each biome can be ignored, the total number of ants can be extrapolated according to the area of different biota.

Of course, this method only applies to ground-dwelling ants, and there are a large number of ants living in trees. Therefore, the research team also included data obtained by the atomizer insecticidal method. This method uses atomized pesticides to kill insects on the vegetation in a specific area, and then collect the dead insects together. The ecological cost and labor cost of this method are relatively high, so this kind of data is very few, but it can also be used as a reference to calculate the number of arboreal ants.

Yellow represents the sample data obtained by litter method, blue represents the sample data obtained by trap method (picture source: original paper) and more. Add up the terrestrial ants and the arboreal ants, and you get 2 × 10 only this data. The number looks large, but the researchers believe that the actual total number of ants is likely to be much more than that.

The study's newsletter author, Patrick Schulte Hayes (Patrick Schultheiss), is almost certain that the true number of ants is higher than 2 × 10: "We are still groping on the surface." On the one hand, this calculation only covers ground-dwelling ants and tree-dwelling ants, and completely excludes underground burrowing ants; in addition, there are few related studies in Central Africa, Southeast Asia and other regions, which may cause some ant-dense areas to be missed.

The ant density of different biota is calculated. Yellow represents litter method, blue represents trap method, and the darker the color is, the higher the density is. (photo source: original paper) Sabine Nooten, one of the authors of the study, also said: "I wouldn't be surprised if the actual total number of ants is an order of magnitude higher than our current estimate."

But for researchers, perhaps the most important result of this study is not the number itself, but that it shows a large number of gaps that still exist in modern research on biodiversity.

Photo Source: Unsplash "some of the data and results we see in textbooks may not be accurate." Wang Runxi, one of the authors of the study, shared the story behind the study in the article, saying, "sometimes these data are even bold speculations made by people based on very limited data in the early days of the study." this knowledge provides important information for us to understand the world, but inadvertently, it also makes us put on a pair of shackles called "classics" and regard them as truth. "

This study does not provide an accurate figure so much as lays the foundation for more related research. Over time, perhaps our understanding of ants and more biodiversity will increase and gradually fill these gaps.

How long has it been since you saw ants?

Reference link:

Https://www.pnas.org/doi/full/10.1073/pnas.2201550119

Https://faculty.washington.edu/timbillo/Readings%20and%20documents/ABRIDGED%20READINGS%20for%20PERU/Wilson_1987_Little_things_that_run.pdf

Https://mp.weixin.qq.com/s/BGMfa4IIYC1DL6t6BlGQcQ

Https://www.nytimes.com/2022/09/22/science/ants-census-20-quadrillion.html

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by: 27, revision: clefable

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