The abundance, biomass, and distribution of ants on Earth

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 × 10¹⁵ and estimate the number of all ants on Earth to be almost 20 × 10¹⁵ 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.

Keywords: Formicidae; density; diversity; insect; worldwide.

Fig. 1.

Global map of sampling locations (n = 1,306) in the dataset, which comprises unique samples (n = 2,355) obtained from leaf-litter extractions (orange circles) or pitfall traps (blue circles) and which reported ant abundances. Some locations contain multiple samples (e.g., from different habitats). The global land surface area is divided into national or regional administrative entities.

Fig. 2.

Estimates of global ant abundance and biomass. (A) The pie chart at center shows the global abundance of epigaeic foraging ants in the leaf litter and the contribution of each biome to the epigaeic ant fauna. The bars on the right show the relative contribution of each biome to global epigaeic ant abundance and land cover. Note that not all biomes are included. The area of the larger gray circle in the background corresponds to the total global abundance of all ants, including arboreal ants and nonforaging individuals. (B) The biomass of the total global ant population in comparison to other selected taxa (data for other taxa from Bar-On et al. (43)). Note that the uncertainty of the terrestrial arthropod biomass estimate is ∼15-fold and that of wild bird biomass is ∼twofold). Biomass values are in megatons of dry carbon (Mt C).

Fig. 3.

Biome-level maps and plots showing mean values of (A) ant density from leaf-litter samples and (B) ant activity density from pitfall trap samples. Mean values were binned into three categories to generate a color gradient, where light and dark shades indicate low and high values, respectively. Hatched patterns mark regions with low confidence for mean value calculations (fewer than six entries). Boxplots show the sample size-weighted mean (red dot), median, upper, and lower quartile. The number of data entries is denoted after each biome name. Data points show values per entry, colored by sample size (natural log scale). Axes are truncated for increased readability. Numerical values of weighted means and SEM are provided in SI Appendix, Table S3.

Fig. 4.

Habitat-level plots showing mean values of (A) ant density from leaf-litter samples and (B) ant activity density from pitfall trap samples. The wide boxplots show the sample size-weighted mean (red dot), median, upper, and lower quartile per habitat; the narrow subboxplots show the data separated into two latitudinal zones: tropical (latitude −23.5° to 23.5°, orange boxplots) and extratropical (latitude <−23.5° and >23.5°, blue boxplots). The numbers in brackets after each habitat denote the number of data entries (overall/tropical/extratropical). Datapoints show values per entry, colored by sample size (natural log scale). Axes are truncated for increased readability, and habitats with fewer than six entries are excluded. Numerical values of weighted means and SEM are provided in SI Appendix, Table S3.