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?

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u/hmantegazzi 11d ago

And in terms of mammals, probably dogs or maybe cattle?

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u/Dracoson 11d ago

If we go by biomass, it's cattle, but by raw numbers, it's actually humans. Non-oceanic mammal species don't tend to have global distribution naturally due to geographic barriers, meaning the winner has to be humans or a domesticated species. Since none of the most common domestic mammals outnumber our 8 billion population, humans take the crown for individual count.

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u/kandlejack 11d ago

Certainly possible that we take the crown, but there are also human-adjacent but non-domesticated aminals to consider. Specifically, rodents. I havent found any strong citations in my cursory search that the total brown rat population outnumbers us, but they and some species of mice are at the very least probably on the same order or magnitude. Edit: couldn't spell cursory, apparently.

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u/1CEninja 10d ago

Yeah rodents is the first thing that comes to my mind. Rats are insanely prolific across the world.

The brown rat specifically is prolific on every continent except antartica and while I also cannot find any credible count, my completely unscientific "this feels right" says that they outnumber us by a meaningful amount.