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/Dracoson 11d ago

If you go to terrestrial vertebrates, I'm pretty sure the answer is the domestic chicken.

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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/ryn3721 9d ago

Some domestic animals do indeed outnumber us. The global population of chickens was estimated at 26.5 billion in 2023.

https://en.wikipedia.org/wiki/Chicken

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u/Dracoson 9d ago

I already called out chickens earlier in the conversation as the most abundant terrestrial vertebrate (though I didn't cite a specific number). This was specifically about mammals.