Nugget of Knowledge: Colour of blood

Ever wondered why a cockroach or a fly doesn’t have red-coloured blood like us? After being haunted by this unusual fact all my childhood, looks like I finally have an answer! 🙂

Blood needn’t, necessarily, be red… Now this makes me wonder – why? And in what more colours can we find it?

I found out that blood, varying from creature to creature, can be of different colours…


The hemo-spectrum chart above gives us a small classification.

Answer to the other question – why is blood coloured differently in  different creatures?

Our blood is red in colour because it has iron-rich haemoglobin (Red Blood C0rpuscles) in it. It used to transfer oxygen from our lungs to other parts of our body. Now, this set-up works good for most vertebrates living in moderate temperatures but for the creatures in deep and freezing-cold water, like octopuses, its not that effective. So their blood is copper-rich to keep them alive in low oxygen-density and high pressure environment. Due to this copper-richness their blood is blue in colour. On the other hand insects (especially roaches) are volumetrically so small that they don’t even need a circulation system for oxygen. Oxygen reaches their body parts through vents and tubes (something like centralized air conditioning). Their blood needs no haemoglobin. It is just used to transfer nutrients. So their blood is white or yellowish in colour because all they have is plasma-like material in their blood. Bugs too, like insects, need no circulation system for oxygen. But since they feed on leaves of plants their blood absorbs a lot of green-pigment. So it changes from yellowish-white to greenish-white.

Interesting right? 🙂

PS: This makes me feel that insects take “you are what you eat” to a whole new level! 😀