Don’t say you’ve never wondered how many ants there are in the world, or whether they weigh more or less than all the whales. However, rough guesses and back-of-the-envelope calculations can now sit down following the publication of a more rigorous analysis. The work is not merely an elaborate way of settling Internet arguments – it could help us understand the role these near-ubiquitous insects play in ecosystems everywhere.
Insects “have long been regarded as the 'little things that run the world',” the team of researchers write, quoting biologist Edward O. Wilson. Despite this, they note, knowledge of their distribution and abundance is low, as scientists have focussed on larger and more charismatic things.
To address this, the authors combined studies of ant abundance in many environments to make estimates on the ground-dwelling and arboreal ants present in almost every major land-based ecosystem. Their figure of 20 quadrillion (20 x 1015) is double E. O. Wilson’s very rough calculation published in 1994 – the first scientific effort to estimate ant numbers by extrapolating from south-eastern England. However, even the paper’s estimate leaves out members of colonies that don’t leave their nests to forage, plus areas such as boreal forests where data is sparse.
Some of the findings may surprise non-entomologists. For one thing, tree-dwelling ants outnumber their ground-dwelling cousins roughly six to one. Those of us who think of ants as creatures who live in underground nests apparently just haven’t spent enough time in rainforests.
Taking into account the diversity of ant weights, the authors conclude that the dry carbon in those quadrillions of little bodies sums to around 12 megatons. If you took the side of Formicidae over cetaceans in the weight contest, you can take a bow. All the wild mammals and birds on the planet add up to around 10 MT, of which whales are just a part.
On the other hand, as a proportion of the total carbon in all the life on Earth, ants are surprisingly actually quite puny. A previous study calculated there is 550 gigatons of carbon – almost 50,000 times as much – incorporated into living things. Most of this is plant life; the trees ants live in weigh a lot more than they do, and fungi and bacteria add up to a lot.
Even among animals, the 15,700 named species of ants don’t stand out. Humans now have about five times as much carbon within our collective bodies as ants do. The chickens, cows, and sheep raised to feed and clothe us have considerably more again. Despite human activity, there are also plenty more fish in the sea (by weight).
The authors hope the work will be useful for studying how biodiversity varies between ecosystems and over time. As they note; “Ants are estimated to excavate up to 13 tons of soil per hectare annually and increase local nutrient availability by an order of magnitude.” Among arthropods, the authors note, ants make up only 1.2 percent of terrestrial species but account for at least 6 percent of the biomass.
Of course, all these calculations could need adjusting if someone decides to release the double-sized ants developed seven years ago into the wild.
The study was published in Proceedings of the National Academy of Sciences.