Washington D.C. [U.S.A.], Mar. 15 : A study shows that global spider population - with a weight of around 25 million tonnes - wipes out an estimated 400-800 million tonnes of prey every year, thus making an essential contribution to maintain the ecological balance of nature.

According to Zoologists at the University of Basel in Switzerland and Lund University in Sweden, more than 90 percent of the prey is insects and springtails (Collembola) and furthermore, large tropical spiders occasionally prey on small vertebrates - frogs, lizards, snakes, fish, birds and bats - or feed on plants.

The study was published in the journal 'The Science of Nature'.

"In concert with other insectivorous animals such as ants and birds, they help to reduce the population densities of insects significantly," said lead author Martin Nyffeler from the University of Basel.

"Spiders thus make an essential contribution to maintaining the ecological balance of nature," he added.

With more than 45,000 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 team has now used calculations to conclude that spiders indeed have an enormous ecological impact as natural enemies of insects.

According to the Food and Agriculture Organisation of the United Nations (FAO), the worldwide human population consumes around 400 million tonnes of meat and fish every 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 tonnes of prey a year.

The zoologists also showed that spiders kill many times more insects in forests and grasslands than in other habitats.

Spiders in these areas catch huge numbers of forest and grassland pests, whereas spiders in desert regions, in the Arctic tundra and in annual crops kill fewer insects in comparison.

The spiders' impact is lower in agricultural areas because they are intensively managed areas that offer unfavourable living conditions for them. (ANI)