Are all the ants as heavy as all the humans?
"If we were to weigh all the ants in the world, they would weigh as much as all of the people," said wildlife presenter Chris Packham recently in BBC Four's The Wonder Of Animals: Ants. But is this statement true?
This claim was originally made by Harvard University professor Edward O Wilson, and the German biologist Bert Hoelldobler, in their 1994 book Journey To The Ants.
They based their estimate on an earlier one by British entomologist C B Williams, who once calculated that the number or insects alive on earth at a given moment was one million trillion.
"If, to take a conservative figure, one percent of this host is ants, their total population is ten thousand trillion," wrote Wilson and Hoelldobler. "Individual workers weigh on average between 1 to 5 mg, according to the species. When combined, all ants in the world taken together weigh about as much as all human beings."
Wilson and Hoelldobler's calculation is based on the idea that the average human weighs a million times more than the average ant. So how well does that stand up to scrutiny? The average adult human weighs 62kg, so that would make the average ant about 60mg.
"There are ants that weigh 60mg, but they're really the big ants," says Francis Ratnieks, Professor of Apiculture at the University of Sussex.
"The common ants which live in British gardens weigh about 1mg or 2mg."
How do you weigh an ant?
"It's very easy to weigh an ant. You buy a small electronic balance, and you place the ant on the balance," says Ratnieks. But he advises you refrigerate it first. "That way it doesn't run away."
Another option is to weigh them in a group, says Mike Fox from BWARS: "I would simply take a suitable container such as a specimen tube and weigh it empty, then put in a counted number of ants, say 100. Weigh again. Deduct the weight of the empty tube and divide it by the number of ants."
With around 13,000 species worldwide, ranging in length from less than 1mm to 30mm, it's probable their weights vary greatly - though most experts seem to agree the average weight of an ant is less than 10mg.
But no-one knows how many ants there are in the world. The BBC Four documentary claims they number not 10,000 trillion but 100 trillion, though it still suggests the total weight of ants equals the total weight of humans.
Experts from the Natural History Museum, Bristol University's Ant Lab, and BWARS (Bees, Wasps and Ants Recording Society), among others, say there is no realistic estimate.
Even by Wilson and Hoelldobler's own figures, their calculation is wrong. There are 7.2 billion humans on the planet today - if we take everyone over the age of 15, they weigh a combined total of about 332bn kg. If we imagine there are 10,000 trillion ants in the world, weighing an average of 4mg, their total weight comes to just 40bn kg.
If we allow for the smaller human population at the time they wrote their book, and a slightly lower average weight, they are still a long way out.
But Ratnieks believes Wilson and Hoelldobler's claim - though untrue in relation to today's world population - would have once been accurate.
"I think if we went back 2,000 years, certainly the ants would've outweighed the humans... but at roughly the time that America became independent , or a little bit before that, that's when we humans became more impressive in our weight than the ants," he says.
"We must also remember that humans are getting fatter all the time. We're not just increasing in population, we're increasing in fatness, so I think we've left the ants behind."
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