Misconception Monday: Is spider silk stronger than steel?

Today’s post will address the 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 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!

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