I recently learned that the reason that spiders have blue blood (I always knew that they had blue blood, but didn't know why) is because their blood doesn't have red blood cells or hemoglobin since they don't have veins, arteries, or capillaries to transport things like iron or oxygen to their organs.
They're just kinda... freefloating around in their bodies, so instead of having a proper circulatory system, their bodies just kinda skip that whole process and just directly coat their organs in their blood and it does the job just fine.
Arthropods are fascinating creatures.
neat, thanks for passing this along










