Viruses are the most abundant biological entities on Earth

Count every living thing on Earth and the winner isn’t bacteria, plants, or animals — it’s viruses. The best estimate puts about 10³¹ virus particles in the biosphere, a 1 followed by 31 zeros.

That dwarfs the roughly 4–6 × 10³⁰ prokaryotes (bacteria and archaea). In oceans and soils, direct counts find about ten times more virus particles than microbial cells. Most are bacteriophages — viruses that infect bacteria.

Put another way: there are around 10⁸ viruses for every human cell, and more phages on Earth than there are stars in the observable universe.

Yet all those viruses add up to only about 5% of the prokaryotic biomass, because each particle is vanishingly small. Tiny as they are, they shape the planet — by killing huge numbers of ocean microbes daily, viruses help drive global carbon and nutrient cycles.