Ants are arguably the greatest success story in the history of
terrestrial metazoa. On average, ants monopolize 15-20% of the
terrestrial animal biomass (total amount of biological matter, not including aquatic animals, nor terrestrial plants and microorganisms), and in tropical regions where ants are especially abundant, they monopolize 25% or more.
Source: Proceedings of the National Academy of Sciences of the United States
of America: In search of ant ancestors