So I’m a Spider, So What?- Kumoko and spider silk

So I’m a Spider, So What?- Spider Silk

Kumoko

 

So I’m a Spider, So What? is an isekai light novel series by Okina Baba that will be getting an anime in 2019.  Now I haven’t read the light novel, but I have read the manga adaptation and to be honest, it really doesn’t do anything ground-breaking or exciting for the most part.  Fans of the genre or RPG style game might enjoy it more than I did.  The reason I am discussing this rather average isekai light novel is due to the main character’s being reincarnated not as a human, but as a spider.  This in and of itself isn’t new, as we have shows like That time I was reincarnated as a Slime, but what is new and different for me is the way it handles the spider abilities of the main character.

 

Spider Silk

Initially, our main character, Kumoko, who is now a spider, is fairly limited in her skill set, having just her spider silk and fangs.  However, as most people know, spider silk is actually surprisingly strong, and is considered stronger than steel, which is correct, but I want to dive into it a bit here.  When discussing how strong spider silk is, there are two terms that we need to know, strength and toughness.  Strength, in this case tensile strength, is the maximum load (weight) a substance can handle before breaking.  In this regard spider silk is indeed stronger than steel, when comparing two strands of equal length and diameter.  Kevlar, a synthetic fiber used to make bullet proof vests, is stronger than spider silk, but it is not as tough.

 

Toughness in material science refers to how much energy a material can absorb before breaking.  Think of it like a rubber band, how far can you stretch the rubber band before it breaks?  So, while Kevlar is stronger than spider silk, it is not as tough.  So while it can hold more weight, it cannot absorb as much energy.  This is highlighted in the graph below.

spider silk

 

In other words, a given length of spider silk can be compressed down to 50% of its starting unaltered length, and pulled out to 5 times its unstretched length.  This gives spider silk a wide range of abilities.

 

But what is it made of?

Spider silk is actually a protein fiber and is actually quite complex.  It also shares some similarities to keratin and collagen, the proteins that make up nails and ligaments, respectively.  On a chemical level spider silk is made up primarily of the amino acids glycine (42%) and alanine (25%).

spider silk

 

Other compounds are also added to the silk to alter its properties, like pyrrolidine, which helps the silk retain water, keeping it moist.  Potassium nitrate is added to prevent the spider silk from breaking down after it is made slightly acidic, to resist bacteria and fungus.

 

How is spider silk made?

Spider silk is made in the silk glands where it exists as a gel-like substance, and does not become silk until it is spun, which is a bit of a misnomer.  This is because spider silk isn’t spun, but rather it is pulled from the gland through a narrow opening, which creates the fiber we know as spider silk.

silk gland

 

In this image you can see how the properties of the spider silk change (pH) as it is pulled out of the gland, with different materials being added in different sections.

 

Are there types of spider silk?

Your answer to this question is probably yes, because there are 35,000 different species of spiders, so logically it stands to reason that there are different types of spider silk.  And you would be correct- there are seven types of spider silk, each made in a different silk gland.

Major Ampulate- Dragline– strongest type of silk
Flagelliform- Viscid- sticky strings of spider silk
Aggregate- Glue like– sticky globs of silk
Minor Ampulate- Minor– temporary web construction
Cylindrical- Cocoon- reproduction
Aciniform- Wrapping- used to secure prey
Piriform- Attachment- part of web formation

spider silk

 

Not every spider has every type of spider silk, but they all have at least three different glands for 3 different types of silk.  The question is, then, how many different types of silk does Kumoko have?

 

Kumoko’s silk

Over the course of the story we see Kumoko specifically reference using several different types of silk: elastic, sticky, poisonous, and sharp threads.  In addition to this we see her use silk in ways that can help us determine the total number of silk types she can make.

 

A web made by Kumoko

kumoko

 

Her web looks like a typical spider web made by an orb weaving spider, and she made it using dragline silk for the thicker lines which support the structure of the web.  The thinner lines building out the rest of web are made using viscid silk.  These are the same types of silk she used to make her elaborate web bridge to fight wasps.

kumoko

 

I also think she probably used attachment silk to make the floor of her bridge.  Another interesting attack used by Kumoko is basically a bolo covered in sticky globs of aggregate or glue-like silk.

kumoko

 

Interestingly enough, there is a spider known as the Bolas spider that hunts using a sticky glob of spider silk at the end of a tether just like what Kumoko does.

 

The final type of spider silk that Kumoko is seen using is aciniform, or wrapping thread.  Aciniform silk is used to wrap up prey, and Kumoko uses it as part of a trap seen below, in addition to its real world uses.

Kumoko

 

There is a group of spiders (Uloboridae) that use aciniform silk to trap, immobilize, and kill their prey, all without using venom.

 

 

 

Conclusion

Thus, I think it’s safe to say that Kumoko can use every type of spider silk except cylindrical spider silk, which is used exclusively for reproduction.

 

Bonus- Real world versions of Kumoko’s skills

There are a number of other skills Kumoko comes up with and uses that are actually used by real world spiders.  Some spiders will place strands of silk around their homes to protect it from ants, which Kumoko also does.

kumoko

 

Some spiders will even use this trick to fish.

spider

 

Poisonous spider silk

Kumoko

 

No, I am not making this up, but there is a group of spiders, the Scytodidae, known as spitting spiders, that can fire off venom-covered strands of silk.

 

 

Spider net

kumoko

 

It is a bit exaggerated here, but, yes, there is a spider that casts nets to catch its prey.  The Deinopidae, or net casting spiders, create a net out of spider silk and use it to hunt.

 

In this case it seems that the truth is indeed as strange as fiction.

 

Second Bonus

I would be extremely remiss if I did not mention one other aspect of spider silk, and that is that spider silk has very high nutrient and energy requirements.  Spider silk is very taxing for a spider to produce metabolically speaking.  Spiders can eat 12 to 32 times their body weight over the course of a year.  As a result, some spiders will eat their own spider webs to reduce the nutrient and energy costs of creating the web.  This would go a long way to explaining why Kumoko is such a glutton, or at least give her an excuse for her gluttony.