Image copyright David E Hill Image caption Spiders are a crucial and underestimated part of the global food web, researchers say

Biologists have calculated that the global population of spiders consumes 400 million to 800 million tonnes of primarily insect prey every year.

Researchers set out to put a value on the ecological importance of the arachnids.

They say their appetite for prey means they consume approximately the same amount as the weight of meat and fish eaten every year by humans.

The findings are published in the journal the Science of Nature.

Dr Martin Nyffeler, the University of Basel scientist who led this study, was inspired by a 1958 book called The World of Spiders, in which a British arachnologist author William Bristowe speculated that the weight of insects killed each year by the British spider population exceeded the combined weight of the British human population.

Since he first considered that, the Swiss arachnologist spent hundreds of hours of recording spider behaviour in the field, and gathering spider ecology studies published around the world.

"These 40 years of gathering experience - spending thousands of hours dealing with spider prey capture rates and prey selection - was needed to be able to write this paper on the global annual prey kill of the spiders," he said in an email.

Image copyright David E Hill Image caption Spiders hunt in a range of habitats from tropical forests to the suburban garden home of this banded garden spider

After these four decades of data-gathering, he had enough information to work out how much the eight-legged creatures consumed.

His numbers are enough to haunt any arachnophobe; Dr Nyffeler says the entire population of the world's spiders - weighing 25 million tonnes - hunts and eats between 400 million and 800 million tonnes of insect prey annually.

But these numbers are not meant to terrify anyone, the scientists hope their study will raise awareness of the importance of spiders in the global food web.

"Spiders kill large numbers of herbivorous insects - and by doing so they help to protect the plants from herbivore damage," said Dr Nyffeler.

"They serve as food for thousands of arthropod-eating animals - an estimated 8,000-10,000 specialised insect species and many passerine birds (an estimated 3,000-5,000 species) feed on spiders."

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