World's biggest, strongest spider webs discovered

Scientists have discovered some of world's biggest, strongest spider webs, one of which, created by Darwin's bark spider, spans over a river in Madagascar.

In 2008, zoologists discovered a river-spanning spider web dwarfing a park ranger in Madagascar.

Made of the world's strongest known biological material, the web is the product of a new species, the Darwin's bark spider, which makes the world's largest webs of any single spider, according to new studies.

Zoologist Ingi Agnarsson of the University of Puerto Rico and colleagues have found Darwin's bark spider webs as wide as 82 feet (25 meters)—about as long as two city buses in Andasibe-Mantadia National Park

Though the new species' webs are overall the world's largest, other spiders might exist that create larger orbs—the spiral at the center of the web—according to study co-author Todd Blackledge, a biologist at the University of Akron in Ohio.

Despite spinning webs of Spider-Man-like size and strength, the Darwin's bark spider uses them to feed mainly on small fry—insects such as mayflies and dragonflies, the team found.

The weavers of the largest Darwin's bark spider webs are almost always female, said Agnarsson.

Juvenile males also weave spider webs, but once they become adults, they abandon this behaviour and instead direct their energies solely to sex.

For survival, the Darwin's bark spider relies in part on its mottled, jagged appearance, which camouflages the spider against trees and—along with Charles Darwin—inspired its name. The species is known to exist only on the island of Madagascar, off Africa's southeastern coast.

Darwin's bark spider webs are made out of two basic kinds of silk, Agnarsson explained.

"Dragline" silk is used to create the supporting strands that anchor the endpoints of an orb web to tree branches overhanging rivers or lakes and forms the radial threads in the web. Stretchier, stickier silk is used to create the spiral that captures prey.

When an insect flies into the web, it becomes stuck, and its struggles causes the silk lines to vibrate, alerting the Darwin's bark spider.

The spider then crawls to the captured insect, and envelops it in a silk cocoon to eat at its leisure.

An analysis of the Darwin's bark spider's silk indicates it's the toughest biological material discovered to date.

"'Tough' means the ability to absorb energy before breaking, and results from a combination of strength and elasticity," National Geographic News quoted Agnarsson, as saying.

Scientists wondered how Darwin's bark spider creates webs wide enough to span bodies of water.

One of the rangers "said the spiders do a Tarzan swing, like they hang down on the silk and swing over. We really, really tried to verify that, but it turned out to be false," said Agnarsson.

He hopes that studies of the species will help shed light on mysteries of spider silk.

The findings appear in the Journal of Arachnology and PLoS ONE.