London, March 15 (IANS) Spiders are one of the most prolific predators and researchers have found that they wipe out an estimated 400-800 million tonnes of prey every year, compared to an estimated 280-500 million tonnes of prey that the world's whales eat.
With more than 45,000 species and a population density of up to 1,000 individuals per square metre, spiders are one of the world's most species-rich and widespread groups of predators, the researchers said.
More than 90 per cent of spider prey is insects and springtails (Collembola).
"Our calculations let us quantify for the first time on a global scale that spiders are major natural enemies of insects," said lead author of the study Martin Nyffeler from the University of Basel in Switzerland.
"In concert with other insectivorous animals such as ants and birds, they help to reduce the population densities of insects significantly," he added.
The findings published in the journal The Science of Nature also showed that spiders kill many times more insects in forests and grasslands than in other habitats.
Due to their secretive lifestyle -- many spiders are nocturnal or live well camouflaged in vegetation -- it was previously difficult to demonstrate their ecological role, but the zoologists at the University of Basel and Lund University in Sweden used calculations to conclude that spiders indeed have an enormous ecological impact as natural enemies of insects.
The researchers used two calculation methods based on different models, which consistently showed that the global spider population (with a weight of around 25 million tons) wipes out an estimated 400-800 million tons of prey every year.
The worldwide human population consumes around 400 million tonnes of meat and fish every year, according to the Food and Agriculture Organisation of the United Nations.
Whales in the world's oceans eat an estimated 280-500 million tonnes of prey a year.