Arachnids are fascinating creatures. Did you know Horseshoe crabs are closely related to arachnids?
they have unique blood -- it's blue - read about it here:
https://en.wikipedia.org/wiki/...
Because their blood is so unique it is used for the detection of bacterial endotoxins in medical applications. The blood of horseshoe crabs is harvested for this purpose.
How neat is that?!