20,000,000,000,000,000 ants are crawling around Earth, researchers find, weighing more in total than all birds and mammals combined

Researchers have worked out an estimate for the number of ants crawling around Earth — and the total is "astounding." 

Scientists at the University of Hong Kong say there are 20,000,000,000,000,000 — that's 20 quadrillion — of the critters around the globe. The combined weight of those ants is more than all of the wild birds and mammals on the planet. 

The weight is also equal to about one-fifth of the total weight of humans. Scientists say the findings, published Monday in the peer-reviewed Proceedings of the National Academy of Sciences, are "conservative."