They may be small, but they sure are mighty. Rather than treating our eight-legged compatriots as something to be squished under a shoe, we should be welcoming spiders as they consume an astonishing amount of insects. Researchers have now calculated this figure as being somewhere in the region of between 362 and 725 million tonnes (400-800 million tons) of insects per year.
With around 45,000 species, spiders are one of the most diverse and widespread groups of predators on the planet, and their impact on the ecosystem is remarkable. While it was known that they did a pretty impressive – and incredibly important – job in consuming insects that are pests, a new study published in The Science of Nature undertook the not so straightforward job of trying to quantify this.
They used two different methods to calculate the total weight of insects consumed globally, one of which is based on a spider's food requirement calculated by their body weight and the other by looking at their annual prey kill in certain environments.
Both methods came up with a similar result, revealing that the 23 million tonnes (25 million tons) of arachnids spread around the planet gobble up between 362 and 725 million tonnes (400 and 800 tons) of insects each and every year. Amazingly, this is comparable to the total amount of prey that all the whales in all the oceans consume, which is thought to be somewhere in the region of 254 to 453 million tonnes (280-500 million tons).
“Our calculations let us quantify for the first time on a global scale that spiders are major natural enemies of insects,” says lead author Martin Nyffeler in a statement. “In concert with other insectivorous animals such as ants and birds, they help to reduce the population densities of insects significantly. Spiders thus make an essential contribution to maintaining the ecological balance of nature.”
The researchers found that the impact of the arachnids' predatory prowess depended on what environment they were living in. Understandably, those living in forests and grasslands were consuming more insect prey than their counterparts living in deserts and tundra, but interesting they were also eating more than those living on crops. This, the researchers suspect, is because the spiders are doing less well in agricultural areas, which offer unfavorable living conditions.
So it seems that the little critters really do punch above their weight, and take their place as some of the most prolific predators roaming our world.
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