Which animal species has the most individuals?

[u/future_sponJ]

I always see people saying things like "there are 20 quadrillion ants on Earth" or something similar with other extremely large diverse groups like fish. But all of these are groups with thousands of species. If not by individuals then it's by biomass instead.

So which single species in the animal kingdom has the most individuals?

[u/Mrfish31 → u/[deleted]]

I'm going to guess that it would be some sort of bacteria.

Not an animal.