A new study suggests that the world’s spiders could eat up to twice the amount of meat that humans do each year.
Biologist Martin Nyffeler of Switzerland’s University of Basel published a paper this week in The Science of Nature on the estimated annual kill count of the world’s spiders.
In an email interview, Nyffeler said he had been studying this question and spider predation for about 40 years after reading a book by naturalist William Bristowe, who speculated that the weight of insects killed by spiders each year would weigh more than the human population of Britain.
Nyffeler took published estimates of spider populations and kill-rates from seven different biomes and extrapolated the likely amount of prey that spiders killed and ate each year.
He found that there were likely about 25 million tonnes of spiders active on Earth each year – equivalent to about 3.3 kg per human, the Gazette estimates. Based on what previous studies found on spider diet, Nyffeler estimated that these spiders would slaughter and devour 400 to 800 million tonnes of prey each year. Humans, in contrast, eat about 400 million tonnes of meat and fish each year.
Nyffeler also found that about 90 per cent of spider prey was insects and springtails, which are tiny soil-dwelling insect-like creatures that can fling themselves high into the air. Spiders also ate frogs, lizards, snakes, fish, birds, bats, nectar, sap and other spiders.
Nyffeler found that about 95 per cent of this consumption happened in forest and grassland regions. Although spiders are often praised as a method of pest control for crops, just two per cent of this consumption happened in croplands, likely due to their frequently disturbed nature.
The study found that spiders exert considerable predatory pressure on other species, both directly through consumption and indirectly through intimidation.
University of Alberta naturalist John Acorn said this was the first scientific estimate of the global spider kill count he’d seen, and that he was surprised by its size.
“It’s a really big number!”
This study shows the ecological significance of spiders when it comes to keeping other bugs in check, and illustrates how researchers have to think of more than just big, visible animals, Acorn said.
“Think in terms of ecosystems.”
The study can be found at link.springer.com/journal/114.
Should Canadians have a constitutional right to clean air and water? A U of A professor is giving a free talk on that issue next week.
Environmental law professor Cameron Jefferies is giving a free lecture Wednesday on adding the right to a healthy environment to the Canadian Charter of Rights and Freedoms.
While Canada has a fairly robust system of environmental laws, Jefferies said Canadians have done a poor job of protecting their natural resources.
“We have First Nations communities across the country that don’t have access to clean water,” he said, as well as highly polluted industrial facilities and rising asthma and cancer rates.
Enshrining the right to clean air, water and soil into the Charter could change this, as the Charter is the basis for all of Canada’s laws, Jefferies said. About 110 nations already have such constitutional protections in place, including France and Norway.
Lawmakers could add such protection to the Charter through an amendment or a more liberal interpretation of its existing protections for life, liberty and security, Jefferies said. Doing so could encourage the creation of stronger environmental laws and prevent leaders from rolling them back as the Harper government did. He was skeptical, however, that leaders had the political will to make such changes.
The talk is at noon March 22 in Room 2-926 at Enterprise Square, which is the place with the big Hudson’s Bay crest on it on Jasper Ave. by 103 St.