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. 

How did they do it?

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.

Nooten says there are 12,000 known species of ants, or 16,000 if you break down all the subspecies, and "still many more species discovered each year."

What's so great about ants, anyway?

So why do scientists want to know how many ants there are? 

"While ants sometimes can really be a nuisance if they invade our kitchens or if they invade us on picnics outside in the parks, they are hugely important in the ecosystems where they occur," Nooten said. 

They help with nutrient cycling, aerate soil, disperse seeds, and decompose biomatter from plants and cadavers.

"So they're doing all these different functions out there. And without them, I think the ecosystems would look very different to what they do now," Nooten said. 

"I think it's really important for us when we go for the forest and have a walk in the park or something, we do not only appreciate the large animals we see, like little fluffy mammals and birds, but we should also look around us and look at the small things which are basically driving and helping to keep our ecosystems running and in check."

Fairweather agrees, and says studying insect biomass can also help us better understand how our planet works, and monitor the effects of climate change.

"This is an extremely understudied area, but is incredibly important to monitor as climates change more and more rapidly. Contextualizing our impact on the planet with numbers, mass, individuals; that's what gets more eyes on the issue," Fairweather said.

It can also help us to track insect populations over time, they said, and get a better sense of how many are being lost to things like climate change, pesticide use, urbanization, agriculture, invasive species distribution and pollution.

In fact, Nooten says a good next step, research-wise, would be to map the ant population on a timeline to see how it's shifted. In follow-up studies, scientists could examine whether they're increasing or decreasing in numbers.

Ants, she says, "do so many different, amazing things." So the next time you have the urge to squash one, she urges you to reconsider.

"If I see one on a picnic, I give it a crumb of cookie or something else to eat and see where it goes," she said.