The enormous amount the spiders eat helps to regulate and control how many pest insects there are in different habitats, mainly in forests and grassland.

Behind the results are Klaus Birkhofer, researcher at the Department of Biology at Lund University in Sweden and at Brandenburg University of Technology Cottbus-Senftenberg in Germany, and his colleague Martin Nyffeler at the University of Basel in Switzerland. Together they have analyzed and calculated how much prey the eight-legged carnivores eat per year.

- A lot of people are scared of spiders and think they are really unpleasant. I hope this study means that people get a better understanding of all the good that spiders do, Klaus Birkhofer says.

If spiders did not eat as many insects and springtails as they do, there would be a lot more damage to crops and forests around the world. But when spiders feast on their prey it brings other positive aspects as well.

- In areas with malaria, for example, the spiders catch mosquitoes that are vectors and can infect people with malaria, says Klaus Birkhofer.

To estimate the amount of spiders in the world, the researchers have used data from 65 previous studies. They have then calculated how much prey the spiders need to kill each year to survive. The answer is somewhere between 400 million tons and 800 million tons.

As a comparison, the world’s total whale population eats between 280 and 500 million tons per year.

More than 90 percent of what the spiders prey on are insects and springtails. Large spiders in tropical areas can also catch and eat, for example, frogs, lizards, birds and bats.

The results of the study are presented in The Science of Nature.