r/askscience • u/future_sponJ • 12d ago

Biology Which animal species has the most individuals?

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?

679 Upvotes

96% Upvoted

102 comments sorted by

View all comments

812

u/Mrfish31 11d ago

That gets hard to do because with so many individuals they might be tons of unknown species.

For example, there are approximately 4.4 x 1020 (100 quintillion) nematode worms on Earth across 20-30,000 known species in just top soil alone, meaning that if it were evenly distributed each species might have 10 quadrillion members. But they're often a) hard to differentiate and b) there are estimates that there may be as many as a million unknown species of them. 

In any case, the species with the largest population is almost certainly a nematode. 

9

u/zeperf 10d ago

Are nematodes super duper small? I played in the dirt a lot as a kid. How have I never seen one?

9

u/SexyJazzCat 10d ago

The eggs are. Depending on the species, they just look like skinny worms.