Alien. There’s something alien about the Atlantic horseshoe crab, (also known as the American horseshoe crab). They’re not even proper crabs – they’re more closely related to spiders, ticks, and scorpions than they are to crabs. A recently discovered fossil found in a dry Illinois creek bed revealed the internal organs of a 310 million year old horseshoe crab in exquisite detail, including its brain. Everything was the same, even the brain structure of the ancient crab was almost identical to that of today’s crabs. They haven’t changed in 310 million years.
It gets weirder. Their blood has strange magical properties. It’s bright blue and contains immune cells that are exceptionally sensitive to toxic bacteria. When these cells meet invading bacteria, they instantly close in and clot around it to protect the rest of its body from toxins. Their milky-blue blood provides the only known natural source of limulus amebocyte lysate, a substance that detects a contaminant called endotoxin. If even tiny amounts of endotoxin-a type of bacteria-make their way into vaccines, injectable drugs, or other sterile pharmaceuticals such as artificial knees and hips, the results can be deadly.
Big pharma around the world rely on these crabs. Scientists figured out how to use the limulus amebocyte lysate to test drugs and vaccines decades ago, and in 1977 the U.S. Food and Drug Administration approved it’s use.
Pharma companies harvest the blue blood each spring when, guided by the full moon, hundreds of thousands of horseshoe crabs scuttle out of the surf and up beaches to lay their eggs. For hungry birds, it’s a feast. For drug companies, this blood harvest is an absolute essential for making human medicines safe. So each May full moon, thousands upon thousands of these primitive creatures are brought en masse to specialised labs along the U.S. East Coast, where technicians hook them up to blue blood milking machines a to extract the blood from a vein near their hearts. Once they are milked they are returned to the sea. It’s a labour intensive, time consuming exercise. A gallon of pure vivid blue limulus amebocyte lysate now costs £48,000 per gallon.
Recherches sur l’anatomie des Limules Paris (1873), is a book by Alphonse Milne-Edwards, a French medical doctor, mammologist, ornithologist and carcinologist (crustacean specialist). Milne-Edwards opens up the alien and lets us look inside.
Credits & reference: “310-million-year-old fossil shows how little horseshoe crab brains have changed” – Josh Davis, Natural History Museum, Science News, 5 August 2021 ; “Horseshoe crab blood is key to making a COVID-19 vaccine – but the ecosystem may suffer.” – Carrie Arnold, National Geographic Science, 6 July 2020 ; Wikipedia ; Images from Biodiversity Heritage Library.