Few earthly creatures predate the horseshoe crab. The animals, which are not true crabs but more closely related to spiders and scorpions, have remained largely unchanged for 350 million years. Their appearance, an exoskeleton defined by a massive domed head and long pointed tail, is unmistakable.
In the 1800s and early 1900s, the crabs were turned into fertilizer and livestock feed used by farms. Horseshoe crab harvests in the Atlantic largely vanished in the mid-1900s after the sea creatures fell out of demand for fertilizer, but returned in the ’90s when they became prized bait for eel and whelk fisheries.
But for most people, horseshoe crabs serve a more practical purpose: Their blood is used to ensure our medicine is safe.
The animals are critical to the work of pharmaceutical companies, especially during this pivotal mass distribution of the coronavirus vaccine. The crabs’ milky blue blood has been used for decades to detect harmful pathogens in medicines, allowing drugmakers to ensure their products are pure before being shipped out and injected into human arms.
The world’s largest population of horseshoe crabs uses the Delaware Bay as a spawning ground, according to the Atlantic States Marine Fisheries Commission. Every year in May and June, thousands of the crabs come ashore along the bay to mate. Each female crab can lay up to 90,000 eggs on the beach. Those eggs make the crabs a keystone species for the bay’s ecosystem, serving as a smorgasbord for hungry fish and shorebirds.
Horseshoe crab blood is the main ingredient in limulus amebocyte lysate (LAL), a compound used by pharmaceutical companies to test drugs for purity, ensuring that bacteria and other pathogens are not tainting the medicine. The crabs’ blood reacts and clots when it encounters harmful endotoxins found in some bacteria, like E. Coli.
But science may have already found the key to wean the pharmaceutical industry off crab blood.
A synthetic replacement for horseshoe crab blood, a new test called recombinant Factor C (rFC), is taking hold in Europe. The U.S. has not yet matched Europe’s embrace of rFC, but that could be coming soon as federal regulators seek to harmonize the nation’s rules with Europe and Japan.
One U.S. drugmaker, Indiana-based Eli Lilly, has already committed to using rFC for any new products it develops in-house. That includes an antibody cocktail treatment for COVID-19, according to Jay Bolden, a biologist who studies rFC for the company.
Instead, the company is making the move for performance, ethics and cost considerations. Helping the migratory birds that feed on horseshoe crab eggs would be a bonus, one that Bolden — a birder himself — understands well.
“We’re moving to rFC as a company for a lot of good reasons, but certainly we can appreciate the impact,” Bolden said.