Spider Silk

Orb Spider Web
Contains 3 Types of Silk

Courtesy & Copyright 2011
Terry Greene, Photographer

Spider silk has long been of interest to scientists and engineers for its incredible strength. Silk can be, by weight, a stronger fiber than steel or Kevlar. But new research has discovered that the strength of the individual fibers does not explain the durability of a web, which can remain functional after sustaining extreme stress. The web’s overall design adds to silk’s durability to create a truly functional product.

Spiders utilize silk for many different reasons – transportation, lining burrows, protecting and securing egg cases, and of course for catching prey. Amazingly, an individual spider has the ability to manufacture several different types of silk, which are used for different purposes. In a typical orb-style web there are at least three kinds of silk at work. One is strong and dry, making up the ‘spokes’ of the web. These are the strands upon which the spider itself moves around, so as not to get stuck in its own trap. The strands which create the characteristic spiral pattern are actually made of two types of silk – one is a fine, stretchy fiber, and the other a sticky, glue-like substance. Together, these two silks make up the part of the web responsible for snaring prey.

Another important property of silk is that when stretched the fiber stiffens. As more pressure is applied, the properties of the silk change, allowing it to become stretchy and flexible. If still more pressure is added, the silk stiffens again, until finally it breaks. Originally, this stiff-stretchy-stiff response to stress was viewed as a weakness, but when analyzed as part of an interconnected web, that’s not the case. A team of scientists from MIT noted that webs could be subjected to a lot of force with only minimal damage. Whether the force was localized – for example while ensnaring a large insect – or more widespread over the entire surface – such as pressure from strong winds – the damage incurred by the web was minimal. Only the individual strands that endure the most pressure break, while others stiffen, flex, and remain intact.

Localized damage allows the spider to more often than not simply repair a web instead of abandoning it and starting over. Creating silk and weaving a web is a costly process for a spider – it takes up a lot of the arachnid’s energy. The ability to simply patch the broken parts is a more efficient strategy which requires less energy expenditure and fewer materials than weaving a new web.

Figuring out how to mimic this response to stress on a material could be infinitely useful in the human world. Imagine a skyscraper in an earthquake that fails in one small place where the forces are strongest – not in its entirety as is currently the case. That same earthquake-damaged building might also need only minimal repairs, saving time, money, and materials. Oh the lessons we could learn from one of nature’s smallest creatures…

Thank you to the Rocky Mountain Power Foundation for supporting the research and development of this Wild About Utah topic. For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

Images: Courtesy & Copyright 2011 Terry Greene
Text:     Andrea Liberatore, Stokes Nature Center in Logan Canyon.

Additional Reading:

Chandler, David L. (2012) How Spider Webs Achieve Their Strength. MIT News Office. Available online at: https://web.mit.edu/newsoffice/2012/spider-web-strength-0202.html

National Science Foundation press release (2012) A Spider Web’s Strength Lies in More Than its Silk. Available online at: https://www.nsf.gov/news/news_summ.jsp?cntn_id=123041

Law, Steven (2012) Curious Things About Spider Webs. Available online at: https://www.ksl.com/?nid=968&sid=20488145

Tarantula Tales

Harietta the Tarantula
at Stokes Nature Center
Courtesy & Copyright 2010
Andrea Liberatore

Aphonopelma iodius
Courtesy & Copyright 2003
James Pitts

Aphonopelma iodius
Courtesy & Copyright 2003
James Pitts

Burrow of Aphonopelma iodius
Courtesy & Copyright 2004
James Pitts

Burrow of Aphonopelma iodius
Courtesy & Copyright 2004
James Pitts

Tarantula crossing the road, Eagle Mountain, UT, click to view larger image, Photo Courtesy & Copyright 2010 Shawna Olsen

Tarantula on a parking lot
University of Utah
20 August 2013
Salt Lake City, UT
Click to view larger image,
Courtesy & Copyright 2013
Lily Marsden

Tarantula on the East Bench, Ogden, UT, click to view larger image, Photo Courtesy & Copyright 2013 Lauren Fowler

Tarantula on the East Bench, Ogden, UT, click to view larger image, Photo Courtesy & Copyright 2013 Lauren Fowler

Hi, I’m Holly Strand from Stokes Nature Center in beautiful Logan Canyon.

Here at the Nature Center, we have an 8 legged staff member named Harrietta. She is a beautiful Chilean Rose Tarantula. Visitors to the Nature Center often exclaim. “Wow! I’m glad those things don’t live around here!” But they are wrong. Tarantulas DO live here as well as in most areas of Utah.

Depending on your source of information Utah is home to either three or four different tarantula species. They’ve been found in the Mojave region in southwestern Utah as well as in the Great Basin.

For a number of reasons few people actually see the tarantulas in the Utah wilds. First of all, Utah is in the far northern part of the tarantula’s distribution range. This means environmental conditions here are less optimal for the spiders than in locations to the south. Secondly, both males and females spend most of their life in and around their burrows, which are dug into the ground in sparsely vegetated areas. As ambush predators, tarantulas lie motionless at the burrow entrance, waiting for an unsuspecting cricket, centipede or even a mouse to wander by. Only then will they dash out of their burrow to bite their victim and pull it back to the safety of their home for feeding. Lastly, tarantulas are nocturnal creatures, venturing out only after most humans have gone inside for the night.

Your best chance to see a tarantula is in the fall. During the months of September and October, mature males roam away from their burrows in search of a female counterpart. In SW Utah large numbers of males can sometimes be seen wandering in search of tarantula love.

In spite of their fearsome appearance, tarantulas are harmless to humans and large pets (e.g., dogs and cats). Their venom is of no medical significance, and, nobody has ever died from such a bite. Most people compare the bite to that of a bee sting and experience no lasting ill-effects other than mild to moderate pain and slight swelling at the site of the bite.

Special thanks to Andrea Liberatore of Stokes Nature Center and Dr. James Pitts of Utah State University’s Dept of Biology for their help with this Wild About Utah topic.

For sources and pictures go to www.wildaboututah.org.

For Wild About Utah and Stokes Nature Center, I’m Holly Strand.
Images:     Courtesy & Copyright 2010 Andrea Liberatore Stokes Nature Center
Courtesy & Copyright 2010 Shawna Olsen
Courtesy & Copyright 2013 Lily Marsden
Courtesy & Copyright 2013 Lauren Fowler
Text:         Andrea Liberatore & Holly Strand,
Stokes Nature Center

Sources & Additional Reading

Allred, Dorald M., B. J. Kaston. 1983. A list of Utah spiders, with their localities. Western North American Naturalist, Vol 43, No 3 https://ojs.lib.byu.edu/ojs/index.php/wnan

Hendrixson, Brett. “So You Found A Tarantula” . American Tarantula Society Headquarters. https://atshq.org/articles/found.html [Accessed July 22, 2010]

Prentice, Thomas R. 1997. Theraphosidae of the Mojave Desert West and North of the Colorado River (Araneae, Mygalomorphae, Theraphosideae) The Journal of Arachnology 25:137–176 https://www.americanarachnology.org/JoA_free
[Accessed July 22, 2010]

Sharp, Jay. “About Tarantulas” Desert USA https://www.desertusa.com/july96/du_taran.html [Accessed July 22, 2010]