Opinion: Unspinning the spider’s web



Daniel Sprockett

For most people, spider webs evoke visions of dusty old attics or dilapidated storage sheds. However, these complex networks of gossamer fibers are one of nature’s most underappreciated feats of evolutionary engineering.

I recently had a chance to learn more about spider webs at Science Café Cleveland, a monthly event organized by Case Western Reserve University and The Great Lakes Brewing Company. January’s topic was “Spider silk: an evolutionary experiment in a biological supermaterial” presented by Dr. Todd Blackledge, an associate biology professor at the University of Akron, and his graduate student, Sam Evans.

Blackledge’s research lies at the intersection of spider behavioral evolution and materials science. For example, he recently co-authored a description of the incredible webs built by Darwin’s Bark Spider (Caerostris darwini) from Madagascar. These spiders construct webs spanning up to 80 feet across lakes and rivers, allowing them to prey on insects that no other spiders can capture. The pressures of such a demanding ecological niche has made its silk 10 times tougher than the Kevlar used to make bulletproof vests.

Many people will be surprised to learn that while all spiders make silk, most of the 41,000 known species of spiders do not make webs. The earliest examples of spider silk preserved in amber date to the Cretaceous period around 140 million years ago, although spider fossils suggest that they’ve been using silk for much longer. Early arachnids first used silk to protect their eggs. Since then, spiders have adapted to use silk for housing, camouflage, dispersal, mating and capturing prey.

The vision of a struggling fly stuck in a spider web is well embossed on the public’s psyche. But if webs are so tacky, why doesn’t the spider stick too? The answer lies in the web’s structure.

Classic spiral orb webs, like that which you might see on the cover of “Charlotte’s Web,” are made up of two distinct types of silk. The first type, dragline silk, is strong and resilient. The spider uses it to string up radial strands like the spokes of a bicycle wheel. The spider then laces these with a second type of silk—the sticky, elastic capture-spiral silk. By only touching the dragline silk, the spider avoids becoming trapped in its own web.

Dragline, capture-spiral, and other types of silk have different properties because they contain different amounts of various proteins. Silk begins its life as protein-rich liquid produced in glands in the spider’s abdomen. The spider secretes this silk rope through leg-like structures on its tail-end called spinnerets. This name can be misleading, since the spinnerets don’t actually spin. This extrusion process causes the proteins to change shape, instantly turning the liquid into a very thin, and very strong, solid strand.

You might have heard that, ounce for ounce, spider’s silk is five times stronger than steel. What you might not have heard is that, since spider silk does not usually trigger an immune response, it’s already being used to make medical implants. Researchers have used spider silk as a scaffold to help re-grow torn knee ligaments, and it could even be used one day to replace medical sutures.

The next time you see a spider web, take a moment to reflect on just how amazing this biological wonder-material really is. It might just save your life!

Daniel Sprockett is a researcher in the KSU Department of Anthropology and a columnist for the Daily Kent Stater. Contact him at [email protected].