Asked by: Steven A Collins, by email
You sometimes hear very large estimates for the biomass of certain animal groups, like ants or nematodes, but these consist of thousands of different, specialised species. The single species with the largest global biomass is likely to be amazingly prolific in one area, or extremely widespread.
Among the most widespread animals are humans. 6.9 billion people averaging 50kg each equals roughly 350 million tonnes. Staggeringly, cow biomass exceeds 650 million tonnes (1.3 billion cattle conservatively weighing 500kg each).
The only wild species in the running is Antarctic Krill. A 2009 global estimate gives 379 million tonnes fresh biomass, but unknown aspects of this shrimp’s ecology make it hard to be sure. By comparison, blue whales (with their krill-based diet) comprised about 35 million tonnes pre-whaling, and about half a million tonnes in 2001.