All arthropods that live on Earth weigh more than humans and livestock: ScienceAlert

Without buzzing, floating, scuttling, or crawling critters, our world would be in conflict. Yet we don’t even know some of the most basic things about these arthropods like butterflies, spiders, and centipedes, like how many of these important components of our world’s biosphere are even out there.

So the researchers crunched some numbers to come to a startling conclusion: Despite their tiny size, the collective overall mass of all terrestrial arthropods is about the same as that of all humans and their farm animals combined.

No wonder they have such an impact on the world we live in.

“Arthropods have been described as ‘the little things that run the world’ because of their central role in multiple ecological processes,” says Yuval Rosenberg, environmental scientist at the Weizmann Institute of Science.

“We need to take them into account if we are to fully understand humanity’s impact on the planet and the possible consequences of climate change.”

Rosenberg and his colleagues therefore amassed 7,000 measurements from the scientific literature. From deserts to farms to rainforests, these records include all major terrestrial habitat types, spread over 300 sites around the world.

They categorized the records into soil arthropods (including plant litter) and aboveground (surface and plant-associated bugs), due to the very different sampling techniques involved for each group.

The data suggests that most of this billion tons of arthropods can be found nestling comfortably on or in the skin of our planet.

Pie chart showing the biomass distribution of different groups of arthropods
Insects like termites dominate the soil biomass of arthropods. (Rosenberg et al., Scientists progress2023)

Termites make up about 40% of arthropod soil biomass, much more than ants at about 10%.

“Each square meter of topsoil contains on average tens of thousands of arthropods, the vast majority of which are tiny mites and springtails“, writes the team in its article.

Only the arthropods that live on and in the ground alone account for about 10 quintillion individuals (i.e. a 1 followed by 19 zeros). These tiny creatures help recycle nutrients in soils, contributing to the global carbon cycle.

The figures reached by researchers for aerial arthropods are much less certain. The team found limited data on flying insects. But combined with the soil group, the mass of these animals is greater than the collective mass of all remaining wild mammals. But there is still an even greater biomass of soil microbes and smaller marine arthropods.

“The figure corrects the impression that we are dealing with infinite and inexhaustible arthropod populations,” says Milo. “Despite their wide distribution, this is not the case.”

Bar chart showing termites make up more biomass than other soil arthropods
The staggering biomass of termites. (Rosenberg et al., Scientists progress2023)

Understanding the distribution of this biomass can help us determine exactly how it fits into larger ecological systems and predict the impact of its decline. For example, understanding the distribution of termites makes it possible to estimate their contribution to global warming.

“(Arthropods) are a tremendous force when it comes to regulating vegetation,” Rosenberg notes. “Thousands of species of birds, reptiles and amphibians depend on them for food, and ultimately arthropods help break down and recycle dead plants and animals, as well as their droppings. This has also have huge implications for us. Even a service that may seem minor, like breaking up excrement, not only fertilizes the soil, but prevents disease and pest outbreaks.”

Worryingly, like much of the rest of life on Earth, terrestrial arthropods, especially flying insects for which there is insufficient data, are also in decline. We rely on these insects to help put food on our tables through pollination and nutrient recycling.

“Quantifying arthropod populations establishes a baseline against which we can measure future changes in arthropod communities and how those changes, in turn, might affect global processes,” Rosenberg concludes.

This research was published in Scientists progress.

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