Researchers at the University of Basel and Lund University in Sweden have shown that spiders wipe out an estimated 400-800 million tons of prey whereas all the humans on Earth, by comparison, consume about 400 million tons of meat and fish every year. With more than 45,000 different species and a population density of up to 1,000 individuals per square meter, spiders are one of the world’s most species-rich and widespread groups of predators. The study also shows that the eating habit of spiders can even be compared to those of the whales, which eat an estimated 280 million to 500 million tons of prey a year.
“Our calculations let us quantify for the first time on a global scale that spiders are major natural enemies of insects. In concert with other insectivorous animals such as ants and birds, they help to reduce the population densities of insects significantly,” Martin Nyffeler, lead author of the study, says in a news release. “Spiders thus make an essential contribution to maintaining the ecological balance of nature.”
Spiders occasionally prey on small vertebrates such frogs, lizards, snakes, fish, birds, and bats and sometimes even feed on plants, but 90 percent of their diet consists of insects and springtails, small insect-like arthropods. Spiders kill many times more insects in forests and grasslands than in other habitats; however their impact is much lower in agricultural areas because intensively managed areas do not offer favorable living conditions for them.