Mammoth structures 80 Feet ( 25 meters ) across
River-Spanning Spider Web
A river-spanning spider web dwarfs a park ranger inMadagascar in 2008. 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, new studies say.
Zoologist Ingi Agnarsson 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 (pictured), “the park rangers knew about them, and I think they’ve shown them to tourists for a while,” said Agnarsson, of the University of Puerto Rico.
Darwin’s Bark Spider Web
An approximately three-foot-wide (meter-wide) Darwin’s bark spider web hangs above a river in Madagascar.
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.
Female Darwin’s Bark Spider
The weavers of the largest Darwin’s bark spider webs are almost always female, such as this spider pictured in 2008, said Agnarsson, a grantee of the National Geographic Society’s Committee for Research and Exploration.
Juvenile males also weave spider webs, but once they become adults, they abandon this behavior 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. (See National Geographic magazineMadagascar pictures.)
Giant Web, Snack-Size Fare
Dozens of mayflies hang helpless in a Darwin’s bark spider’s web in 2008.
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.
Unlike most spiders, Darwin’s bark spiders will sometimes wrap several insect corpses into a single cocoon, creating a snack pack for later consumption.
Darwin’s Bark Booby Trap
One of the first things Agnarsson’s team wondered after learning about the Darwin’s bark spider was exactly how it creates webs wide enough to span bodies of water, such as this river in Madagascar’s Andasibe National Park, pictured in 2010.
One of the rangers “said the spiders do a Tarzan swing, like they hang down on the silk and swing over,” Agnarsson said. “We really, really tried to verify that, but it turned out to be false.”