20 Quadrillion Ants

How many ants are there in the world? It’s the kind of dreamy question you might have briefly asked yourself as a kid on a lazy summer day as you were checking out an anthill that was teeming with the busy little creatures, just in one corner of your backyard. Sometimes, though, the subject of a child’s idle wonder becomes a scientist’s challenge–and Nature has published an article that tries to answer that question.

The first step in the challenge is trying to come up with a mechanism that would allow you to approximate the number of ants on Earth, because you obviously couldn’t count them, one by one, even if all of those notoriously active insects would oblige you by holding still. To give you a sense of scale, there are 15,700 named species and subspecies of ants. They are found in and on virtually every piece of dry land in the world and in the widest possible range of habitats, including cities, deserts, woodlands, grasslands, and especially rain forests. The National Wildlife Federation website states that the only land areas that don’t have ants are Antarctica, Greenland, Iceland, and a handful of islands.

So how can the Nature researchers hope to count them? By piecing together the findings of 489 independent studies that have attempted to count ant populations on every continent and in every habitats where they are found, using standard ant-counting methods. By extrapolating from this direct data, the researchers estimate that there are 20 quadrillion–that’s 20,000,000,000,000,000–ants in the world. That’s a lot of ants. But that finding admittedly doesn’t give a complete picture, because there are no studies of how many ants live underground or in trees. 20 quadrillion therefore could easily be an undercount.

But the Nature researchers didn’t stop there. They wondered how much all of those ants would weigh, did the math, and concluded that the 20 quadrillion ants would have a biomass of 12 million tons of carbon, which is more than all of the world’s birds and animals combined. (Carbon accounts for about half the weight of ants.) And, as the researchers point out, we should be glad there are so many ants around, because they play a crucial role in the ecosystem in multiple ways, including serving as food for many species.

Ants are also kind of fascinating to watch on a lazy summer afternoon, too.