A team of Swiss and Swedish scientists calculated that they kill between 400 million and 800 million tonnes of prey.
Compare this annual prey intake to those of humans and other animals: all humans eat about 400 million tons of meat and fish, while whales feed on up to 500 million tons of seafood.
Over 45,000 species of spider live across the world and have a collective weight of about 25 million tons.
Researchers Martin Nyffeler and Klaus Birkhofer compiled data from 65 previous studies to estimate the number of spiders in the world. In addition to eating insects, big, tropical spiders will also prey on small vertebrates like frogs and fish from time to time, or eat plants.
It is news that no arachnophobe will wish to hear - but spiders are one of the world's most voracious predators after devouring a whopping 800 million tons of prey each year.
Spiders evolved from an arachnid ancestor during the Devonian period around 400 million years ago.
"Spiders thus make an essential contribution to maintaining the ecological balance of nature". Most spiders reside in forests, grasslands, shrublands, croplands, and deserts.
Another fun fact: Spiders have a population density up to 1,000 spiders per square meter.
"These estimates emphasize the important role that spider predation plays in semi-natural and natural habitats, as many economically important pests and disease vectors breed in those forest and grassland biomes", says lead author Nyffeler.
Of course, spiders are just part of the food chain, and are frequently eaten themselves: Between 8,000 and 10,000 predators feed exclusively on spiders, while spiders are also an important part of the diet of an estimated 3,000 to 5,000 bird species. The scientific journal The Science of Nature has published the results.
"We hope that these estimates and their significant magnitude raise public awareness and increase the level of appreciation for the important global role of spiders in terrestrial food webs", adds Nyffeler.