All the spiders in the world combined annually eat about 440 to 880 million tons of insects and other pests — equal to the weight of more than 85 million elephants, according to a new study.
That's a lot of bugs.
In comparison, all humans combined consume an estimated 440 million tons of meat and fish annually. Whales feed on 300 to 550 million tons of seafood, while the world’s total seabird population eats an estimated 77 million tons of fish and other seafood.
Most spiders, of which there are some 45,000 species, are found in forests, grasslands and shrublands, followed by croplands, deserts, urban areas and tundra areas. And their ravenous appetite keeps countless insect pests in check.
The spiders serve to protect plants and trees by eating the bugs that would feed on them, especially in forests and grassland areas, according to study lead author Martin Nyffeler of the University of Basel in Switzerland.
“Our calculations let us quantify for the first time on a global scale that spiders are major natural enemies of insects," Nyffeler said. "In concert with other insectivorous animals such as ants and birds, they help to reduce the population densities of insects significantly.
"Spiders thus make an essential contribution to maintaining the ecological balance of nature."
All spiders are carnivorous, feeding predominantly on insects and to a lesser extent on other spiders, the study said. Larger species of spiders are also known to chow down on frogs, lizards, snakes, fish, birds and bats.
It's hard to estimate the number of spiders in the world. A Pitish scientist speculated in 1947 that there were about 2.2 trillion spiders — in England and Wales alone, Nyffeler told LiveScience.
Sometimes just being a spider is scary enough to insects: In recent years, researchers have shown spiders not only eat bugs, they can also intimidate them to the point where insects eat less in the presence of spiders.
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.
Nyffeler has been studying spiders for 40 years and used data from 65 previous studies to determine these estimates.
"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," stated the study, which appeared in the European journal The Science of Nature.
