The estimate is two to twenty times higher than previous ones, according to the study, published Monday in the journal Proceedings of the National Academy of Sciences.
“We were very surprised by the large number of ants we found,” Sabine S. Nooten, an insect ecologist and temporary principal investigator at the University of Würzburg in Germany, told CNN on Tuesday. Nooten was co-lead author of the study.
“We had virtually no expectations because the numbers that were previously floating around in the scientific literature were basically educated guesses and they had very little empirical data to base them on,” she added. “And that’s what’s new about our study, because we synthesized the data from many empirical studies.”
The previous global estimate of between 1 trillion and 10 trillion ants by the renowned biologists Bert Hölldobler and Edward O. Wilson assumed that they roughly balance each other out 1% of the world’s estimated insect population of 1 quintillion individuals, according to the study.
However, the research team behind this latest study based the new estimate on observational evidence from a large dataset of globally distributed ant samples. The authors identified and evaluated 465 eligible studies with 1,306 sampling sites covering all continents and major biomes inhabited by ants.
Nooten says scientists could use the study’s comprehensive dataset, spanning 80 years, to predict what future communities or environments might be like. For example, the team estimated the number of ground-dwelling ants, which densely populate tropical and subtropical regions such as the South American forests, at around 3 quadrillion.
“We may already be able to see changes over time in our data set,” co-first author Patrick Schultheiss, a temporary principal investigator at the University of Würzburg, told CNN. Schultheiss emphasized that changes in agriculture or the way forests were cleared could have an impact on ant numbers.
“No one has ever compiled a data set on ants anywhere in the world,” Schultheiss said. He added that while they knew from studies that ant counts in the tropical forests of West Africa were very high compared to regions in the Arctic, “we didn’t know what the picture was – how many numbers there were.”
According to the study, the estimated ant abundance exceeds the combined biomass – i.e. the total mass – of wild birds and mammals and corresponds to about 20% of human biomass.
“A surprisingly common question I get asked is, ‘How many ants are there on earth?’ and while there are some estimates, none of the numbers used have felt robust,” Adam Hart, professor of science communication at the University of Gloucestershire, England, told CNN. Hart, who is also vice-president of Britain’s Royal Entomological Society, was not involved in the study.
“This new study, based on nearly 500 studies from around the world, gives us the best answer yet to this tricky question. The amazing thing is not just the total number, but the fraction of the biomass that ants make up—one-fifth of the biomass of all humans. It really underscores how important ants really are,” he added.
A “conservative” figure
The estimated total is almost unimaginably large, but the study authors said it was “conservative.” This is because they couldn’t collect all the data they wanted to include.
For example, many ants live underground, but no studies are available that can provide numbers on how many, Schultheiss said. There are ants in the extreme north and in the extreme south, as in sub-Antarctica region, but there have not been enough studies of ants in these areas to make a mathematical estimate.
Citizen scientists could fill in those gaps, according to Schultheiss, who said non-scientists, even schoolchildren, could powerfully contribute to the dataset simply by collecting leaves, pulling out all the ants, and counting how many there are.
“We hope to inspire people, above all, to respect nature, to enjoy nature, because it’s just amazing what ants can do and to what extent. But even if they are willing to contribute to science with a very simple method, even very simple data can have tremendous value,” he added.