Because spiders have such a complex (and fascinating) anatomy, I decided to break it up into two parts.

To just say the anatomy of a spider consists of two body parts, eight legs and varying range of eyes, wouldn’t be fair to the other parts that make them who they are. One of my favorite parts of a spider, is their lungs. Spiders have what’s called “book lungs”*, which are much more intricate than those of humans. Where our lungs are located in our thorax, the lungs of a spider are located in their abdomen. Book lungs work as stacks of interchanging air pockets and tissues filled with hemolymph (spider blood) which give them the appearance of a books page. Just like humans, their lungs exchange oxygen and carbon dioxide through diffusion.

*Note- Not all species have book lungs.

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A spider’s web is made up of protein fibers called “silk”. As mentioned before in the previous article, a spider’s silk is the strongest natural material. It’s composed of proteins made of various amino acids. It can hold strengths in temperature elements from  -40° to 428°. Yes, you read that right. If you’ve ever had a chance to run into the Darwin’s bark spider (Caerostris darwini), would you have believed their silk is the strongest spider silk that’s been discovered thus far? It’s known that their silk is 10 times stronger than kevlar! 10 TIMES! Now we know why their silk can be so inspiring to engineers!

Microscopic view of a spiders spinneret’s, courtesy of MicroAngela.

The yellow garden spider (Argiope autantia) is a great example of an arachnid using its silk for multiple purposes. It has been discovered that this particular species has 5 different types of silk they can produce. The dragline (also known as the major ampullate) is what’s used for a webs outer rim and spokes. It’s tough and totally means business. The silk used for the lines inside the web is sticky, so that’s cause for a different type of silk. This silk is called the capture spiral (flagelliform). As they produce this, they add in a little “spider goop” to help create an overall stickiness. Thus resulting in the sticky web that captures the prey. In order to protect their egg sac they use a silk called tubiliform (cylindriform silk). This is their stiffest silk made to keep the eggs safe, even if it fell from a branch. The minor ampullate is more of a “duct tape” silk, used for temporary construction until their new web is up. And what would a spiders silk be without having one specifically for wrapping their prey? This would be know as the aciniform silk. The complexity of all of the above just shows that spiders aren’t just eight-legged creeps. They’re a small part of our world that has an incredible intricate system.

Yellow garden spider (argiope autantia) courtesy of Steven T.

The first ecdysis (molt) for a spider usually begins while it’s still in the egg sac. For all spiders, the will molt until they reach maturity. For some spiders, they’ll continue to molt for the rest of their lives. Everything is brand new once a spider molts- from fangs to toes. In order for a tarantula to molt, they usually start on their back (but can molt in other positions, too). If you didn’t know any better, you might think they would have died (wrong position)! From there, they “pop the top” of their carapace and squeeeeze out to reveal a translucent body that needs to take time to harden. This will depend on their size and can take anywhere from minutes (baby spiders) to hours (BIG spiders). Other spiders, such as those that live on webs, can create a dragline and molt while hanging from their web. Talk about living on the edge!

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  Holothele Incei (Trinidad Gold Dwarf) spiderlings emerging from egg sac. (Source)

As mentioned in the last article, all spiders (that have eyes) have what are called “simple” eyes. Meaning, they aren’t compound like other insects. In the insect world, if you have eyes, they’re either simple or compound. The difference is quite easy. Compound eyes would be that of arthropods such as flies, bees and beetles. Though, it’s not just limited to those species. They are made up of hundreds or even thousands of mesh-like units that work as a network to provide sight. Each unit is called ommatidia. The ommatidia is the optical unit that houses the cornea, lens and photoreceptors that determine lightness and darkness.

Simple eyes are much less complex than compound eyes. They contain one single lens, rather than multiples.This gives those with single lenses less of advantage as those with compound eyes have a greater viewing field. Though, as we learned in my last article, most spiders have terrible eye sight anyways. Thus, proving we learn to live and adapt with our shortcomings.