May 3, 2005— A mystery: Do spiders spin silk with different, lethal properties, or is it how spiders use the silk in their webs that counts?

The secret to the deadly trap of a spider web turns out to reside in both material and deployment, researchers are discovering as they analyze the deadly effectiveness of spider silk.

"Spiders are unique because they spin silk for so many different ecological functions," said Todd Blackledge, assistant professor of biology at the University of Akron in Ohio. "This has resulted in the evolution of a diverse toolkit of silks. We are discovering that these silks have a variety of physical properties and underlying genetic structures."

Blackledge and colleagues Adam Summers and Cheryl Hayashi decided to focus on black widow silks because the poisonous spiders construct a "very typical" cobweb.

Black widows are near the base of the evolutionary tree for the cobweb-weaving spider family Theridiidae.

The spider's large size and prevalence in certain parts of the country also made it a prime candidate for the study, published earlier this year in the journal Zoology.

According to the journal paper, black widows use a steel-like silk covered in a torturous glue to snare their prey. They then lasso and bind the prey in with a more spring-like silk.

The super-strong dragline silk makes up the supporting frame and radii of their webs. This same silk is coated with droplets of glue to make "gumfoots," or lines of web that are attached to the ground.

Prey insects minding their own business that get stuck on a gumfoot usually are goners.

"The gumfoot is attached to the ground in such a way that it easily breaks free from the ground when an insect sticks to the gluey foot portion," Blackledge told Discovery News. "The gumfoot is under a little tension so that it will actually lift insects into the air where they can't get a foothold to be able to struggle free."

The black widow likely then will subject the victim to the capture spiral, which is made of weaker, but more flexible, silk.

Like rope in a cowboy's lasso, the capture spiral silk can wrap around prey, now locked into the steel-strong web jail. Rendered powerless, the victim will be killed and eaten.

Capture spiral silk can form "windlasses," which are springy, silk coils. Some experts have theorized that the windlasses give capture spiral silk its stretchiness, and that the glue gives dragline silk its strength.

To test out these theories, Blackledge and his colleagues collected 25 webs from seven different black widow species. They mounted the webs onto cardboard and used a high-tech electronic tensile tester to study various elements of the silks' strength.

They also took digital images, which they used to perform similar strength tests virtually using a computer software program.

The researchers then compared the resulting data with 276 capture spiral webs taken from several orb-weaving spiders that are common to gardens in the southwest, where the study was conducted.

Blackledge and his team determined that the windlasses and the glue did not contribute much to the capture silk's flexibility or to the dragline silk's toughness. Instead, they now believe the differences between the silks are due to the fibers' underlying amino acids.

The secret to the strength of dragline silk, which probably could absorb the impact of a bullet if it could be woven into clothing, is that its amino acids join into tight crystals, which make the silk's protein fibers stiff and strong.

Capture silk, on the other hand, is made up of coiled protein chains that can spring, stretch and rebound.

"This offers exciting potential for the production of biomimetic fibers because we may ultimately be able to use our understanding of spider silks to individually engineer fibers for custom purposes," Blackledge said.

Randy Lewis, professor of molecular biology at the University of Wyoming, who has previously speculated about silk proteins, said he and his colleagues "are in complete agreement with the conclusions from (the Zoology paper) data."

Lewis, along with Blackledge, hopes black widow webs, and the silks secreted by other spiders, will inspire new manmade materials in future.