According to About.com
The total biomass of all the ants on Earth is roughly equal to the total biomass of all the people on Earth.
Is the above statement just a myth or its in fact real? Are there any hard facts to prove this?
Ants drastically outweigh us
If it's good enough for you, the first sentence of Ted Shultz, "In Search of Ant Ancestors," PNAS, December 19, 2000 vol. 97 no. 26, 14028-14029:
Ants are arguably the greatest success story in the history of terrestrial metazoa. On average, ants monopolize 15–20% of the terrestrial animal biomass, and in tropical regions where ants are especially abundant, they monopolize 25% or more.
He gives no reference to a primary source, and that's the closest I can find to a solid reference via the Internet. PNAS is one of the most prestigious journals in the United States, so I think we can trust peer review not to let the opening sentence of a paper be boloney (knock on wood!).
The most likely book I can think of to contain an authoritative discussion is Wilson's The Ants (1990). I don't have it on hand, but it won a Pulitzer, so it's available at many libraries. One part field guide, one part textbook -- if you're interested in ants you should definitely check it out sometime :).
See this table on Wikipedia if you want to pursue more details on human biomass vs. other species. Hard numbers are of course hard to pin down, but the gist is that ants probably outweigh us by an order of magnitude, and termites and krill compete with them for first place.
An article recently published by the BBC debunks this myth: http://www.bbc.co.uk/news/magazine-29281253
This claim was originally made by Harvard University professor Edward O Wilson, and the German biologist Bert Hoelldobler, in their 1994 book Journey To The Ants.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."
The article there also points out that nobody really knows the actual number of ants in the world:
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.
Coupled with the fact that Wilson and Hoelldobler's own calculation is wrong:
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.
It doesn't seem to hold true that this idea holds any weight. However it was possibly true at one point in history:
"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."