Error in 'The Economist'

This is either a flat-out error or just bad grammar:

"the weight of the Formicidae family is equal to that of the world's population of humans and accounts for 10% of the biomass of all the creatures on the planet."

from this article

That implies that humans make 10% of the biomass of Earth.  This seemed wrong, so I looked it up.  The estimated biomass of ants ranges from 900 to 9,000 million tons, while the biomass of humans is about 100 million tons.

Now, if you added up humans, livestock, and crop plants, you might get 10% of Earth's biomass.  Crops have a biomass of 2,000 million tons.

You should always have an internal fact-checker on everything you read or hear.  You don't have to memorize a lot of facts, but you should have a feeling for how things relate to each other.  Developing this fact-checker requires that you have a lot of background knowledge, and an ability to notice something that 'seems wrong'.