In a paper just published in PNAS (Proceedings of the National Academy of Sciences), “The abundance, biomass, and distribution of ants on Earth”, the authors attempt to estimate the total ant population of the Earth, counting all species. They conclude,
The astounding ubiquity of ants has prompted many naturalists to contemplate their exact number on Earth, but systematic and empirically derived estimates are lacking. Integrating data from all continents and major biomes, we conservatively estimate 20\times 10^{15} (20 quadrillion) ants on Earth, with a total biomass of 12 megatons of dry carbon. This exceeds the combined biomass of wild birds and mammals and equals 20% of human biomass. Ant abundance is distributed unevenly on Earth, peaking in the tropics and varying sixfold among habitats. Our global map of ant abundance expands our understanding of the geography of ant diversity and provides a baseline for predicting ants’ responses to worrying environmental changes that currently impact insect biomass.
Here is the abstract:
Knowledge on the distribution and abundance of organisms is fundamental to understanding their roles within ecosystems and their ecological importance for other taxa. Such knowledge is currently lacking for insects, which have long been regarded as the “little things that run the world”. Even for ubiquitous insects, such as ants, which are of tremendous ecological significance, there is currently neither a reliable estimate of their total number on Earth nor of their abundance in particular biomes or habitats. We compile data on ground-dwelling and arboreal ants to obtain an empirical estimate of global ant abundance. Our analysis is based on 489 studies, spanning all continents, major biomes, and habitats. We conservatively estimate total abundance of ground-dwelling ants at over 3\times 10^{15} and estimate the number of all ants on Earth to be almost 20\times 10^{15} individuals. The latter corresponds to a biomass of ∼12 megatons of dry carbon. This exceeds the combined biomass of wild birds and mammals and is equivalent to ∼20% of human biomass. Abundances of ground-dwelling ants are strongly concentrated in tropical and subtropical regions but vary substantially across habitats. The density of leaf-litter ants is highest in forests, while the numbers of actively ground-foraging ants are highest in arid regions. This study highlights the central role ants play in terrestrial ecosystems but also major ecological and geographic gaps in our current knowledge. Our results provide a crucial baseline for exploring environmental drivers of ant-abundance patterns and for tracking the responses of insects to environmental change.
The full text of the article is behind a paywall, but an article in the Washington Post, “Scientists have calculated how many ants are on Earth. The number is so big it’s ‘unimaginable.’ ” has more details.
Interestingly, in their 1991 encyclopedic work The Ants, Edward O. Wilson and Bert Hölldobler estimated the global ant population at 10 quadrillion, within a factor of two of this work.
With Earth’s human population around eight billion, that means there are around two and a half million ants for every person on the planet (and yet the humans still outweigh the ants by a factor of five).
We often think of the biosphere as so prolific it dwarfs the works of man, but as of 2014 an article in Forbes, “How Many Transistors Have Ever Shipped?”, estimated the total number of transistors which had been manufactured since its 1947 invention at 2.9\times 10^{21} devices (including those on integrated circuit chips), or, if transistors were equally divided up among ants, enough to give each ant 145,000. With the exponential growth in circuit density and computer memory capacity, the number of transistors today is doubtless much larger than in 2014.