Spiders Make Stronger Silk to Catch Bigger Prey

August 7, 2008

Common house spiders adjust their weapons depending on the task, says a new study that found the species weaves webs of stronger silk when bigger insects are more abundant.

The skill allows house spiders to save energy by weaving easier-to-make, weaker silk strings when their prey is smaller.

"We knew from our past research on black widows that cobweb spiders adjust their web architectures in response to different availabilities of prey," said study author Todd Blackledge at the University of Akron, in Ohio.

"But we didn't know much about how spiders might alter the silk used to spin cobwebs," he said.

Common house spiders—(Achaearanea tepidariorum)—are members of the Theridiidae family of cobweb spiders, which includes the black widow.

(Learn about black widow spiders.)

Up to the Task

Researchers fed 27 common house spiders identical weights of either large, fast-moving crickets or small, slow-moving pill bugs for a week. Later, they examined the spiders' silk.

The team found that silk threads spun by the spiders that had been given faster food were thicker, stiffer, and better at shock absorption.

"Silk spun by spiders fed crickets could support twice as much weight as silk spun by spiders fed pill bugs," said study co-author Cecilia Boutry, also of the University of Akron.

"A single thread from their web could support a cricket twice as heavy as the spider itself without breaking," she said.

The authors suggest that the spiders could be sensing the prey that they are encountering and building silk that is appropriate for the task.

The change of diet might also affect the type of webs the spiders weave, they say.

The research was recently published online in the Journal of Experimental Zoology.

Chemistry of Strength

"The complexity of what these spiders are able to do is pretty striking," said zoologist Brook Swanson of Gonzaga University in Spokane, Washington.

"Spider silk is being revealed to be not just one substance, but an array of compounds that can do different things," said Swanson, who was not involved in the study.

Because of its incredible strength and shock absorbing properties, spider silk is the subject of research aiming harness the natural technology for bulletproof armor and other materials.

"We need to tease apart whether these silks are being woven in different ways by the spiders or if they are in fact chemically different from one another," Swanson said.

"Once we figure that out, we may be able to replicate this variation when we make [artificial] silk in the lab."

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