Researchers set out “to document the impact of the global spider community as insect predators” — and the numbers are impressive.
Spiders feed on an estimated 400 to 800 million tons of insect prey annually, according to a new study published in Springer’s journal The Science of Nature.
Martin Nyffeler, University of Basel in Switzerland, and Klaus Birkhofer, Lund University in Sweden and Brandenburg University of Technology Cottbus-Senftenberg in Germany, authored the study. To draw this conclusion, they first estimated about 25 million tons of spiders roam the Earth by sifting through dozens of prior studies of spider values from seven different regions of similar climate.
“There are few groups of terrestrial predaceous arthropods that can compare with spiders in terms of abundance and biomass,” the study says. An exception to that are ants, who feed on both plants and animals.
Two methods were used to calculate the number of prey killed by spiders: In one method, researchers estimated the number based on the spiders’ food requirements per unit body weight and their biomass values from other studies. In the second method, they assessed the spiders’ annual prey kill based off of prey censuses in the field and web density estimates.
To put this in perspective, the study says humans consume an estimated 400 million tons of meat and fish annually. Another startling comparison is to whales, who consume about 280-500 million tons annually. And by contrast, the study says the annual food consumption of seabirds on Earth is estimated at 70 million tons.
“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,” the study concludes. “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.”