My husband and I rented a Jeep in Baja, Mexico, and drove up the coast to a sleepy town called Todos Santos. The drive was even prettier than usual thanks to a recent, unexpected deluge of rain. Desert shrubs, with a mix of sand and cactii, were in full bloom, and almost glowed with green. Blue-ish mountains lay to one side, and the turquoise sea glistened ahead. Making the picture all the more alien and complete were the lovely splatters of yellow blood.
Some kind of insect was rupturing in front of our eyes, spilling out almost-neon yellow blood onto our windshield. It was as if the insects knew their brilliant yellow blood was the one color missing from our surreal desert palette and said what the heck, let’s make the sacrifice for the sake of art. I’m not really sure what type of insects they were, but we noticed yellow butterflies floating about the region. Aha, yellow butterflies must be hitting our car and dying in big yellow mess! Or, it could have been the boring ol’ flies.
What I do know for certain after doing some reading is that all insects have yellow, and sometimes green, blood. The reason it’s not red like ours is that it lacks iron, which looks red when paired with oxygen. The surface of Mars and rust are also red due to iron and oxygen.
We humans have lungs and a heart that work together to pump oxygen efficiently all around our body: to our brains, organs, cells and even our little toes. The helpful molecule that carries the oxygen around is called hemoglobin, which contains iron. The iron in our blood is a juicy red when bound with oxygen; without oxygen, our blood is a darker maroon. Incidentally, veins look blue because red light from the blood is absorbed by our skin, while blue light, which has shorter wavelengths, travels through.
If somebody were to bleed blue blood, you would know right away they are not human — and perhaps some form of crab. Crabs and other creatures use a different molecule to shepherd oxygen around their bodies, hemocyanin, which uses copper instead of iron. The cool thing about copper is that is turns blue when the mood is right.
Insects don’t need blood to breathe. They have openings all over their bodies called tracheae that allow the air to rush in to the cells and organs that need the oxygen. Instead, their blood sloshes around their bodies, transporting fluids and waste. This fluid is typically a pale yellow or green.
By the way, if you see a fly bleed red, don’t be confused. The red substance is actually from a pigment in their eyes. Somehow that’s grosser than blood.
So why were the insects sacrificed on our jeep loaded with such a vivid yellow fluid? I know why it isn’t red, but I couldn’t find anything online to explain what precise substance is behind the yellow hue. If you know the answer, please do tell. Or if you happen to squash any insects that explode with neon yellow blood, please send photos — just for fun.
Nice article on mollusks and blue blood at The Straight Dope.