Published: Thu, March 16, 2017
Science | By Boyd Webster

Spiders Eat More Each Year Than All Humans Put Together

Spiders Eat More Each Year Than All Humans Put Together

Their conclusion: altogether there are about 25 million metric tons' worth of them around.

Inspired by a book called The World of Spiders, Dr. Martin Nyffeler of the University of Basel spent thousands of hours studying the prey selection and capture rates of spiders.

Incredibly, they're capable of killing between 400 million and 800 million tons of prey annually.

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.

Spiders mostly consume insects but the largest tropical species occasionally make a meal of vertebrates such as frogs, lizards, fish and small mammals, say experts. "Spiders thus make an essential contribution to maintaining the ecological balance of nature", he adds. The figure reflects the fact that forests, grasslands and savannas are less frequently disturbed than for instance agricultural or urban areas, and therefore allow for greater spider biomass.

The stunning numbers comes from a study conducted by scientists from the University of Basel in Switzerland and Lund University in Sweden.

In comparison, spiders in deserts, the Arctic tundra, and annual crops kill fewer insects.

This showed just how big a role spiders play in keeping pests and disease-carriers at bay - especially in forests and grasslands where a lot of them live.

Taking into account the various density of spider populations across different environments and spiders' food requirements per unit of body weight - plus prey census data from previous field studies - the researchers estimate that spiders consume somewhere between 400 and 800 million tonnes of prey each year. The spider's eating habits can even be compared to those of the whales (Cetacea) in the world's oceans, which eat an estimated 280-500 million tons of prey a year.

The findings are reported in The Science of Nature.

"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", Dr. Nyffeler said.

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