Misconception Monday: Is spider silk stronger than steel?

In keeping with the theme of these next few weeks (spider silk), today’s post will address a common idea: that spider silk is stronger than steel. In researching the topic of spider silk, I kept coming across this “fact” in articles across the web, with a number of writers quoting that “spider” silk was specifically five times stronger than steel or tougher than Kevlar, or a myriad of other weird claims. Although I certainly believe that some spider silks could be stronger than steel, what concerned me initially about this statement is that it seems too simple to always be true. To begin with, I found it hard to believe that any scientist(s) had experimentally tested the tensile strength of silk of all 40,000+ species of spider. In addition, spider silk varies quite a bit in composition, so to think that all spider silk was exactly (or even approximately) 5x stronger than steel seems unlikely, even if spider silk in general is stronger than steel. Therefore, I set out on a mission to find where this statement might have originated…. and sort of came up empty.

That is, while there have been many studies of the basic physical properties of spider silk (here’s one example: Griffiths&Salanitri1980), fewer than 100 species have actually had their silk tested. Why the idea that spider silk is 5x stronger than steel is so widespread, I’m not exactly sure. My guess is that someone must have calculated this once, for one species, and one specific steel alloy, and then it somehow caught on because it sounds interesting and is easy to remember.

In conclusion, this MM topic is going under the category of true for some species, with an additional note that the phrase “spider silk is stronger than steel” is misleading and needs further testing. Why? Because spiders are highly variable, within and across species, and to claim that every spider in the world produces silk that is stronger than steel would simply be unfounded. However, direct measurements of spider silk have shown that some spider silk can have a tensile strength that is higher than that of certain steel alloys. While this may not be as cool of a fact to state at a party (because I’m sure everyone talks about spider silk at parties…), you would not be misinforming your friends!

Spider of the Week – Black-and-yellow Argiope

For this week, I’m featuring another common, and highly photogenic orbweaver of the Americas: Argiope aurantia. I was out doing field work today, and these spiders were EVERYWHERE! Must be mating time. They are so beautiful, and very large (females can be almost 1.5″ long), so my camera can actually handle taking nice pictures of them. I’m only posting the pictures that I took today, but there are tons of awesome pictures of this species online if you do a little searching. Lots of videos, too.

Adult female Argiope aurantia
Adult female Argiope aurantia

So, what’s interesting about this species, you ask (besides that it is awe-inspiring… )? First, its current scientific name, Argiope aurantia, describes the colors of the spider, as Argiope means “silver-faced” and aurantia is derived from a word meaning “gold” (See wikipedia for a list of its previous scientific names and this website for a longer history of the name “Argiope aurantia”). In the western U.S., this species is commonly referred to as the Golden Orbweaver or the Golden Silk Orbweaver. However, in the southern U.S., this species is commonly referred to as the Black-and-yellow Argiope, and a different species (Nevila clavipes) is commonly referred to as the Golden Orbweaver, causing some confusion as to what the common name of Argiope aurantia should be. Other common names it has are the Yellow Garden Spider, and the Writing Spider, plus varieties of all of its common names pop up here and there. It’s interesting how the same species can have so many different names, presumably because it spans such a large region of the world.

Their webs are nothing short of spectacular. A couple of the webs I saw today had perfect orbs that were almost two feet in diameter, though others were a little more normal, coming in around 6in-1ft. I saw some females sitting directly in the center of their webs, and others were off sitting on leaves or branches about one foot away, waiting for prey to fly into the web (or hiding from me). Curiously, individuals of this species build their webs with a zig-zag (adults) or circular (juveniles) stabilimentum, that is rather conspicuous (at least to humans). There are various hypotheses as to why they might do this, and supposedly these structures inspired E.B. White in writing Charlotte’s Web (See more on the hypotheses here and here).

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Adult female Argiope aurantia in web with zig-zag stabilimentum.

Because of their size, capturing large prey isn’t difficult. I saw one capture a very large grasshopper, but I had unfortunately left my camera in the car and couldn’t film it. However, it looked something like this and she did not stop to eat it once she had wrapped it up. Like other orbweavers, she will probably leave it until nighttime, when she takes down her web, and eats it, before building a new one. When I had my camera with me later, I found another web that had a few small insects wrapped up in it (see example below).

Insect (a bee I think) that was wrapped up in an Argiope aurantia web.
Insect (a bee I think) that was wrapped up in an Argiope aurantia web.

This species is NOT a danger to humans, despite how large and brightly-colored individuals are (See this discussion for more info). So, don’t be scared if you see any around in the next few months. Especially since they are so beautiful!

Misconception Monday – All spiders and insects belong outside the home.

I think that most people have one of two basic reactions whenever they come across a spider (or any other arthropod/bug) in their home. There is…

1) “ACKK that thing is sooo gross ewww UGH smush it/get it out of here/flush it down the toilet!!!”

or there is…

2) “Aww poor lil’ guy, why are you inside? Let’s put you back outside where you belong!”

While the tone is a bit different in each of these reactions, the message is the same: many humans believe that bugs don’t belong inside the home. Yet, we find them in our homes all the time, and we spend a lot of time/money trying to eradicate them. So, then, is it true that spiders don’t belong “inside,” and if not, why do we feel this way?

The answer to the first part of the posed question is simply, no. As much as we humans like to separate ourselves from all other animals and from nature in general, we are a huge part of the natural world. And, as part of the natural world, many animals have evolved to coexist with us and our cosmopolitan ways, spiders included. Though there surely can be species that roam into homes randomly from time to time, there are a number of spiders that live in/on man-made structures for their entire lives. For example, the Common House Spider (Parasteatoda tepidariorum) prefers to build webs on or in buildings (if you live in the U.S., you have probably seen them in barns, sheds, attics, etc.). Moving these spiders and other house spiders to bushes or trees outside would not help them survive, and would be an unnatural habitat for many spiders found in the home.

Answering the second part of the posed question is a bit simpler: we don’t like seeing spiders in our homes because we think that they are pests. However, spiders are more like pest control, than pests, themselves. Many house spiders eat insects like mosquitoes, fruit flies, ants, and cockroaches – essentially, all the bugs that we really don’t want in our homes.

So, if you can, try to accept the spiders that you see hanging out in your house, because they’re more likely helping you than harming. However, if you really can’t stand the sight of them, and you absolutely have to move them somewhere else, try to move them into a shed, or attic/closet you don’t access much, instead of outside.

Things I Learned This Week

What did I learn about spiders this week?

Someone discovered a new species!

This might be one of the most beautiful creatures I have ever seen: The Mirror Spider.

Spiders have enemies too…

Adorable jumping spider… if only there were a way to figure out what it’s thinking.

Came across this interesting study again.

One of many reasons for why it’s important to study spiders.

Another random NASA experiment with spiders: Spiders on Drugs

Have a good weekend!

Spider of the Week – The European Garden Spider

One of the things that I love most about my job is the chance to learn something new and exciting everyday, even when I am on vacation. For instance, while I was home in the SF Bay Area last weekend, my dad decided to show me a number of cool spiders that he has found recently while gardening. One of them was this beautiful, and seemingly common orbweaver, Araneus diadematus. I’m sure that I saw this species a thousand times growing up, but being afraid of spiders, never took the time to really appreciate how interesting and beautiful it really is. Here are a couple pictures I took of a male next to my parents’ house, but if you click on a few of the hyperlinks in this post, you can see some professional photos of them. ARKive has some great videos, as well.

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Some facts about Araneus diadematus:

  • Commonly known as the “European Garden Spider,” or the “Cross Orbweaver.” The “Cross” name comes from the distinctive pattern on the dorsal side (the “back”) of the abdomen.
  • Occurs throughout North America and Europe.
  • Sexual cannibalism does occur in this species. In this case, females will sometimes eat males either before or after sex, depending on a variety of physical states (e.g. how hungry she is). (See: Roggenbucketal2011)
  • Like many orbweavers, individuals will take down their webs at night, eat the web (along with any insects that are caught in the web), and build a new web in the morning.
  • Spiderlings disperse through a behavior called “ballooning,” in which individuals release a bit of silk that catches in the wind, carrying the spider away from its original home. (More info on ballooning in spiders)