October 28, 2025 — The American horseshoe crab is not the most glamorous or endearing animal. With its long, spiky tail, helmet-shaped shell and ten eyes, the 445-million-year-old species did not get this far relying on its good looks. But in this annual event, called a mass spawning, the crabs leave behind tens of thousands of eggs, which contribute to a wider ecosystem along the Eastern Seaboard and allow the ancient species to continue thriving.
Since the 1980s, humans have prized horseshoe crabs for another reason: The invertebrates’ light blue blood has likely benefitted anyone who has ever received a vaccine or flu shot. Equipped with a system that detects toxins as soon as they enter the crabs’ bloodstream, the blood is a key ingredient in a product that can detect contaminants in medicines. Pharmaceutical companies use the mechanism to ensure their drugs are safe. But amid concerns for the horseshoe crab population, conservationists, biotechnology experts and drug manufacturers alike have spent decades pushing for the adoption of synthetic alternatives that don’t harm the animal.
This spring, that effort reached a new milestone. For the first time, the industry’s primary regulatory body, the U.S. Pharmacopeia, officially recognized the alternatives as an option for companies to test vaccines. Now, 11 major pharmaceutical companies have reported an initial shift or intent to shift to these alternatives in a survey conducted by conservation groups. And the biggest producer of the blood-derived product publicly backed the crabless alternatives this summer.