Developments in Brief : Scientists Probe the Mystery of Why Spider’s Silky Web Is Strong as Steel

Experiments with gels in a Scottish laboratory may have unraveled the secret of spider webs, which are made of a mysterious silk that, for its weight, is as strong as steel.

Aracheologists, or spider scientists, long have puzzled over how the silk can be so strong when it is made of a fluid from the spider’s glands. “The popular theory has been that it hardens when it hits air, but that’s never really held up under chemical analysis,” said Jacqueline M. Palmer of Harvard University’s Museum of Comparative Zoology.

Now scientists in Glascow are reporting that the silk used by spiders is probably a unique type of polymer that hardens as it is pulled and elongated. Polymers are natural substances with molecules arranged in repeating patterns, much like the rungs on a ladder. Chemists say the patterned structure of polymers makes them unusually strong.

The Scottish scientists discovered that some types of polymers gel when a drop is allowed to fall from a pipe, trailing a filament behind it. Under the microscope, they found these filaments had a gel core encased by a solid structure of molecules.

In a report in Nature magazine, the scientists concluded that the pulling motion of the polymer drop caused molecules in the filament to quickly align in a strong, solid structure.

“Generally strength is gained by lots of molecule bonds in an order, so this would make sense,” Palmer said. The silky threads can vary in width from one-quarter of a millimeter to one-quarter of a micron, she said. A micron is one-thousandth of a millimeter.

Some spiders spin a new web every day, then eat the protein-rich substance and recycle it. Other spiders build webs to last months.