Spider Webs – Stronger Than Steel 20 Feb 2013

Imagine designing and creating a rope only an inch thick, able to stretch without breaking 2-4 times its normal length but strong enough to stop a huge airliner. Then add to the requirements that it can’t be made of metal or any presently used fiber, but only of spider silk. Impossible, you say! Actually, it’s very realistic. The strands spiders use to spin webs are stronger than steel, more resilient than Kevlar – the material that bulletproof vests are made of, yet finer than a human hair. If you could somehow weave spider webs into a cable, you’d have that airplane-stopping tether. Spiders have been performing the advanced biochemistry needed to generate webs for about 100 million years, but even with modern technology, we still can’t duplicate their process.

Perhaps as long as humans have been around, we’ve been fascinated or frightened by these 8-legged creatures. They are all venomous to some degree, but most don’t have the dental apparatus necessary to penetrate our skin. Most all spin some sort of web, some of great beauty and symmetry such as garden spiders, the orb weavers that make large circular webs in bushes as summer draws to a close. In the children’s story “Charlotte’s Web,” the friendly, wise, philosopher star of the narrative was an orb weaver.

If you’ve ever watched the web weaving process, you know that it is a complicated business. The spider spans great distances creating trusses, support members and reinforcing structures all designed to catch a meal. Frequently destroyed by wind, birds and blundering large insects, the spider may eat the remnants of its web and recycle the bits to make new snares. Only the spiral strands connecting radial supports are sticky. Most spiders place blobs of glue at intervals along those threads, but some produce silk coated uniformly with adhesive.

Spider silk is produced by small internal glands and released from tiny openings at the end of their abdomen. Different types of silk are produced as needed. Specialized glands produce only glue, others yield walking threads, cementing threads, silk used to wrap prey, strands for egg sacs, and material for the core of sticky threads.

Many years ago, physicians placed spider webs on open wounds to stop bleeding, and in the belief that they were antiseptic. They probably did help to retard bleeding by providing a nucleus for clotting, but it has never been shown that there is anything in or on spider silk that controls bacterial growth.

Interestingly, webs from black widow spiders have been used as cross-hairs in bombsights of World War II bombers and in telescopic rifle sights. One amateur astronomer harvests web fibers from black widows for use in the optics on his telescope. He carefully tapes the spider down, tickles its spinnerets with a dental probe and winds the resulting silk on empty 35 mm slide mounts before placing the fibers in his lenses. Much thinner than the crosshairs supplied by the manufacturer, he says they are easier to use when tracking stars during celestial photography.

Scientists are experimenting with spider silk to see if it might be used like that from silk worms. However, the spider web strands are so thin it would take, according to Cornell University researchers, 400 spiders to make a single yard of cloth. Other work is being undertaken to unravel spider biochemistry so their silk can be synthesized and mass produced. In the future, parachutes, safety belts and even artificial tendons and ligaments might be made from this substance. Anita Manning in USA Today writes that Dr. Randy Lewis at the University of Wyoming has used spider silk sutures in rats and mice and found that they cause no allergic or other tissue reactions and are less prone to ripping out. The sutures held up without deteriorating for longer than two weeks.

So, next time you walk through one of those dangling, clingy, sticky, nearly invisible webs, brush it off, think kindly thoughts, and be grateful. One day you may be able to brag that your latest incision is being held together by spider webs!

Dr. Risk is a professor emeritus in the College of Forestry and Agriculture at Stephen F. Austin State University in Nacogdoches, Texas. Content © Paul H. Risk, Ph.D. All rights reserved, except where otherwise noted. Click paulrisk2@gmail.com to send questions, comments, or request permission for use.