Their conclusion was that there are 25m tonnes of spiders around the world and that, collectively, these arachnids consume between 400m and 800m tonnes of animal prey every year. This puts spiders in the same predatory league as humans as a species, and whales as a group. Each of these consumes, on an annual basis, in the region of 400m tonnes of other animals.
Martin Nyffeler of the University of Basel and Klaus Birkhofer of Lund University, quoted in the Economist.
“An estimated 400–800 million tons of prey are annually killed by the global spider community” Link