Our research published today provides a predictable answer. We conservatively estimate that there are about 20 quadrillion ants on our planet. That’s 20 thousand million million, or in numerical terms, 20,000,000,000,000,000 (15 with 20 zeros).
We further estimate that the world’s ants collectively create about 12 million tons of dry carbon. This is more than the combined mass of all wild birds and wild mammals in the world. This is also about one fifth of the total weight of humans.
The eminent biologist Edward O’Wilson once said that insects and other invertebrates are “the little things that run the world”—and he was right. Ants, in particular, are an important part of nature. Among other roles, ants disperse soil, disperse seeds, break down organic material, create habitat for other animals, and form an important part of the food chain.
Estimating the number and mass of ants provides an important baseline from which to monitor ant populations amid worrying environmental changes.
Counting the world’s ants
There are over 15,700 named species and subspecies of ants, and many others not yet named by science. The high level of social organization of ants has enabled them to colonize almost all ecosystems and regions around the world.
The surprising ubiquity of ants has led many naturalists to consider their exact numbers on Earth. But these were basically educated guesses. There has been a lack of systematic, evidence-based estimates.
Our research included an analysis of 489 studies of ant populations conducted by fellow ant scientists from around the world. It included non-English literature in languages such as Spanish, French, German, Russian, Mandarin and Portuguese.
The research spanned all continents and major habitats including forests, deserts, grasslands, and cities. They used standardized methods to collect and count ants such as pitfall traps and leaf litter samples. As you can imagine, this is often a tedious task.
From all this, we estimate that there are about 20 quadrillion ants on Earth. This figure, although conservative, is between two and 20 times higher than previous estimates.
Previous data adopted a “top-down” approach assuming that ants comprise about 1% of the world’s estimated insect population. In contrast, our “bottom-up” estimation is more reliable because it directly uses data on ants observed in the field and produces fewer estimates.
Our next step was to find out how much all these ants weigh. The mass of organisms is usually measured in terms of their carbon makeup. We estimated that 20 quadrillion average-sized ants correspond to a dry weight or “biomass” of about 12 million tons of carbon.
This is more than the combined biomass of wild birds and mammals – and about 20% of the total human biomass.
Carbon makes up about half of an ant’s dry weight. If the weights of other physical elements are included, the total mass of the world’s ants would still be greater.
We also found that ants are unevenly distributed on the earth’s surface. They vary sixfold between habitats and generally peak in the tropics. This underscores the importance of tropical regions in maintaining healthy ant populations.
Ants were also particularly abundant in forests and surprisingly dry areas. But they become less common in man-made habitats.
Our findings come with some caveats. For example, the sample locations in our dataset are unevenly distributed across geographic regions. And most of the samples were collected from the ground layer, meaning we have little information about the number of ants in trees or underground. This means that our conclusions are somewhat incomplete.
we all need ants
Ants also provide important “ecosystem services” for humans. For example, a recent study found that ants may be more effective at helping farmers prepare food than insecticides.
Ants have also developed close interactions with other organisms – and some species cannot survive without them.
For example, some birds rely on ants to take out their prey. And thousands of plant species either feed or house the ants, or spread their seeds in exchange for protection. And many ants are predators, helping to keep populations of other insects under control.
Alarmingly, global pest numbers are declining due to threats such as habitat destruction and fragmentation, chemical use, invasive species, and climate change.
But data on insect biodiversity is dangerously scarce. We hope that our study provides a baseline for further research to help fill this gap.
It is in the interest of humanity to monitor ant populations. Ants aren’t hard to count, and citizen scientists around the world can help investigate how these important animals are faring at a time of great environmental change.
by Mark Wong, Forest Fellow, University of Western Australia; Benot Génard, Associate Professor, University of Hong Kong; François Brassard, PhD candidate, Charles Darwin University; Patrick Schultheis, Provisional Principal Investigator, Julius Maximilian University of Würzburg; Ranxi Wang, PhD candidate, University of Hong Kong; and Sabine Knuten, Provisional Principal Investigator, Julius Maximilian University of Würzburg
(Conversation)
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