“Are there more animals than people?”

… asks my niece Lane.  We’re over at a Christmas party at her house.  She’s eight years old, blond, and has huge blue eyes, and so cannot be denied.  “Sure,” I say, “There are probably more ants in this town than people in all the world.”

“I don’t mean bugs, I mean animals.”  She has two dogs and a snake, and if you include the squirrels in the yard, there are more animals than people in just her household.

“Well, there are a lot of chickens,” I say. Given that we each eat a few chickens a year there have to be a couple billion in just the US. Fortunately, the Food and Agriculture Organization of the UN tracks these sort of things, and lists them here.   They count ~18 billion chickens in 2009 in the world, one for every 2.5 people.  They also count 1.4 billion cattle, and about a billion sheep and a billion pigs.

“Not food, wild animals!” she says, getting exasperated.

“OK, there are probably more mice than people,” I offer, but actually have no idea. That seems to satisfy her, though.  There have to be more mice than anything else because every carnivore feeds on them.

When I go to look it up, I find that no one knows how many mice there are in the world.   The estimates of the number of mice per square mile vary all over the place, from 7000 per square mile from a study in Hays, Kansas in one year, to zero in a year of drought.    If you figure 1000 mice per square mile on average in forested land, and there are about 20M square miles of forest in the world, then there would be 20 billion mice.  So I did not lead my niece astray!

Still, mice are tiny, so there being a lot of them doesn’t count for that much.  Suppose we multiply the number of animals by their size, and so find the animals that have the most weight in the world.    Here are a few candidates:

Animal Population (billions) Weight (kg) Total Weight (millions of tons)
Cattle 1.4 400 560
Humans 7.0 70 490
Pigs 1.0 70 70
Chickens 18.0 3 54
Elephants 0.0007 4000 2.8
Mice 20 (?) 0.020 0.40

So there’s more mass of human flesh than of any other kind of land animal on the planet, except for cattle. That’s a kind of icky thought, but kids are into ickiness.  I could have phrased it that way to Lane, but there’s a sure way to become known as a weird uncle!

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One Response to “Are there more animals than people?”

  1. mtraven says:

    I know your niece doesn’t count ants, but they are reputed to make up a remarkable 15-20% of all terrestrial animal biomass — probably more than humans. That is a total across many different species of course, so not directly comparable to the other entries in your table.

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