How many ants are there? The number is 'incredibly difficult to comprehend'

There are so many ants on the planet, the human brain can barely comprehend it, says the German insect ecologist who helped calculate the number.

In a new study published in the Proceedings of the National Academy of Sciences, a group of scientists examined data from 489 ant studies and used those findings to estimate the number of the critters currently walking the Earth.

The final tally was 20 quadrillion. That's 20 thousand million millions, or 20,000,000,000,000,000 with 16 zeroes. And it's likely an underestimate.

"I'm stunned," Sabine Nooten, a University of Würzburg insect ecologist and one of the lead authors of the study, told As It Happens host Nil Köksal. "It's incredibly difficult to comprehend. It's amazingly awesome as well."

Put another way, the combined biomass of the world's ants is greater than that of every wild bird and non-human mammal put together. And while they're most common in tropical climates, they can be found in a variety of habitats on every continent. 

And they're all out there, doing their busy work, interrupting picnics and playing an important role in maintaining global ecosystems. 

To come up with their tally, Nooten and her colleagues looked at hundreds of studies from around the world in different languages. 

The studies themselves tended use one of two methods to calculate various ant populations. One is to collect sample leaf litter: "This is really neat because you can use one square metre of a forest floor, take all the leaf litter and extract the ants from this leaf litter. And then you count all the ants in this area and you can, in the end, scale up from this area and extrapolate on the global surface," Nooten said.

The other is to use pitfall traps for the ants and wait for them to fall in, and use those totals to extrapolate wider populations.

Aaron Fairweather, a PhD candidate at the University of Guelph who studies ants and other insects, says the study's methodology is "very impressive and sound," and its global scope is "a huge undertaking."

"Understanding that there are quadrillions of ants on the planet is incredible and unfathomable. The fact that we have the means to begin to understand that is even more amazing," they said.

"We now start to have a glimpse into what global ant life on the planet looks like. That said, in my opinion, this is likely an underestimate of the total volume of ants on the planet."

That's partly because the existing methods of calculating ant populations are limited and unable to account for the critters that live beneath the soil and in vegetation, Fairweather said.

But it's also because there are entire species of ants that have yet to be discovered.