They sure do, and here’s why!
I find spiders creepy and terrifying (irrationally, I’m afraid, as there are no spiders in the UK that are harmful to humans… except, of course, for the ones that sneak in on crates of bananas and such), but I also find them absolutely fascinating.
However, “spiders” is a phenomenally large subject and so today I confine myself only to the colour of their blood, which is blue.
Okay, poetic license and all that, things are never quite so straightforward: spiders do not actually have blood, as such. The substance that they use to perform the same function as blood does in our own bodies is actually called “Hemolymph”.
This difference arises because spiders have something called an “open circulatory system”, which basically means that there are no blood vessels (arteries, veins etc.) and that the creature’s body cavity is filled with the fluid. It surrounds every cell and bathes every organ, somewhat different to the way our own system works!
Forget about that though, as it is mere definition and nothing more than biological sophistry; the fact remains that spider blood, or hemolymph, is not red.
Human blood is red for the simple reason that it is based on the molecule haemoglobin, which contains iron: iron is reddish in colour when oxidised and it is this that gives our oxygenated blood its colour (our de-oxygenated blood is also red (iron content), but a much darker shade; it only looks bluish due to the colour of our veins and the filtering effect of looking at it through skin…).
In the case of spiders though, aliens that they are, the oxygen is bound to a different molecule, a protein called hemocyanin, which is copper based. Hemocyanin is colourless when deoxygenated, but will turn dark blue when exposed to the air (as it is when the spider bleeds).
So spiders have blue blood!
If you want to verify any of this (and please feel free to correct me ifI have made any errors, or have oversimplified to the point that I have lied!) then there is plenty of literature around, as well as all the usual blogs and online encyclopaedias.
With that in mind, please don’t go and cut up any spiders to see for yourself: they have a right to life too!