National Geographic Daily News
A male missing sector orb weaver spider.
A male Zygiella x-notata spider on a white background (file picture).

Photograph by Stefan Sollfors, Science Faction/Corbis

Matt Kaplan

for National Geographic News

Published June 2, 2011

Scientists may have uncovered why spiders are so creepy-crawly—they have more legs than they need, a new study says.

After collecting thousands of female spiders in the wild, scientists found that more than 10 percent of the arachnids were missing at least one of their eight legs.

"We wondered if this was handicapping them in any way," said study co-author Alain Pasquet at the University of Nancy 1 in France.

The research team placed 123 Zygiella x-notata spiders in individual plastic boxes, where the animals could build webs. Sixty of the spiders were eight-legged, while 63 were each missing one or more legs. (See spider-web pictures.)

Pasquet and his colleagues found that webs built by spiders missing at least one leg did not differ much from the webs built by spiders that were intact.

(See pictures: "World's Biggest, Strongest Spider Webs Found.")

Six-Legged Spiders Still Good Hunters

The scientists then placed flies in the enclosures and found that leg-lacking spiders were also perfectly capable of catching and eating the insects.

"We were really surprised—we expected missing a leg to harm the spiders' ability to catch food, and it didn't at all," Pasquet said.

(Watch a video of the world's largest spider.)

Based on the findings, the authors propose that spiders have legs that they don't really need—an advantage when it comes to escaping a predator that's put the bite on a limb, for example.

Yet there does appear to be a limit to how many legs a spider can lose. In the wild, the team found few spiders missing more than two legs. And in the lab, these five-legged spiders built shoddy webs.

Spider-legs study published in a recent issue of the journal Naturwissenschaften.

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