> ❔ What's your favorite story involving weird blood? Here's [a list](https://tvtropes.org/pmwiki/pmwiki.php/Main/AlienBlood), if you want to jog your memory. The priestess flared her wings in a shaky semblance of a threat display. “My body is not for sale.” Her father's copper-bladed knife sliced her skin as easily as the thin mountain air.  “That isn’t your decision to make.” Blue blood welled and dripped into the cauldron. It burbled — & soon, he was rich. --- ## AFTERWORD There's an old saying — truth is stranger than fiction. I like to think that when I take inspiration from the world around us, I add creative depth to the fantasy universes I create, because reality lets me be braver and gives me a place to start. For this edition of the newsletter, I wanted to take a look at how I do creature creation for my stories. It's important to me to riff off little-known and unique animals, because it's a great way to help people learn more about the remarkable world we live in. When coming up with the original idea for the people of Eheu Isle, I was actually inspired by lore about elves. Specifically, the idea that faerie has an allergy to iron. It's a common motif in Irish mythology, perhaps related to an oral tradition about the impact of iron weapons on the indigenous people — or perhaps not. Most blood, which is vital to the survival of most species, is iron-based. The more I thought about elves and faeries being allergic to iron, the more I wondered what _their_ blood looked like. In her article about [the properties of vampire blood](https://www.ithilear.com/2017/09/the-powerful-properties-of-vampire-blood.html), Beth Alvarez discusses how the 1991 novel _The Vampire Diaries_ is the origin of the idea that vampire blood has healing properties. But how plausible is this? More plausible than I thought, honestly. Horseshoe crabs, along with some other arthropods, mollusks and crustaceans, are among the few animals on Earth who have hemocyanin instead of hemoglobin in their blood. Hemocyanin is one of the [strongest known antigens](https://biosyncorp.com/klh/introduction_to_hemocyanins/). Antigens can stimulate strong immune responses, so hemocyanin is often harvested from horseshoe crabs to help vaccine development. Put simply, the blood of a horseshoe crab can help humans heal. Hemocyanin has a [copper base](https://animals.mom.com/relatives-horseshoe-crabs-5041.html); instead of the more typical iron-based blood that humans and most other terrestrial animals have. Proteins that actively use copper in their chemical makeup are rare: there are only about eight. This is just one more way the humble horseshoe crab is a ripe source of inspiration for inventing fantasy species, especially those who [can be harmed by iron](https://tvtropes.org/pmwiki/pmwiki.php/Main/ColdIron) — fairies and elves being the most common example. The reverse is possible too, by the way: people who are allergic to shrimp and crustaceans may actually be allergic to hemocyanin proteins. Hemocyanin is a [cross-reactive allergen](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/hemocyanin) of crustacean, cockroach, and dust mites. Creatures with copper-based blood use the protein hemocyanin instead of hemoglobin to carry oxygen to their cells. Unlike hemoglobin, which is typically blue but turns red in the presence of oxygen, hemocyanin is clear until exposed to the air — then it turns blue. Creatures modeled on horseshoe crabs would therefore bleed blue instead of red. If humanoid, their skin tones — particularly while flushed — will be bluish instead of pinkish. Most hemocyanins are inefficient compared to hemoglobin, efficient as hemoglobin at transporting oxygen per amount of blood. The exception to this is in a [cold, high-pressure environment](https://blogs.scientificamerican.com/octopus-chronicles/octopuses-survive-sub-zero-temps-thanks-to-specialized-blue-blood/). Genetic alterations in blue blood is responsible for allowing the octopus to colonize the oceans, warm and cold. I wrote about this in the [thermoregulation](https://eleanorkonik.com/thermoregulation/) %% ( [[2021-08-23 Thermoregulation]] ) %% edition. Species that evolved in environments with low oxygen or high gravity (or both) — places like the ocean deeps, or high mountains, or even space — might have blue blood. Examples include the ["genies" in the Honor Harrington universe](https://en.everybodywiki.com/List_of_alien_species_in_the_Honorverse) or the [Outsiders of Larry Niven's Known Space universe](https://larryniven.fandom.com/wiki/Outsider). And, of course, the winged inhabitants of Eheu Isle. It's not just blue blood that's plausible, though. High levels of biliverdin (enough to kill a human) in the hemoglobin of Papua New Guinea's skinks turn the lizards' blood green. The [ocellated icefish](https://www.nationalgeographic.com/animals/article/150312-blood-antarctica-octopus-animals-science-colors) lives in such an oxygenated environment that it has neither hemoglobin nor hemocyanin; its blood runs clear. Its lack of scales and oversized heart help oxygen get through the body. > ❔ What's your favorite story involving weird blood? Here's [a list](https://tvtropes.org/pmwiki/pmwiki.php/Main/AlienBlood), if you want to jog your memory.