What If Gone

Species → Atlantic Horseshoe Crab

Atlantic Horseshoe Crab

Limulus polyphemus

About 500,000 horseshoe crabs harvested each year for the biomedical…
Extinction risk Vulnerable
OverfishingMarine environmentFoundation species
Atlantic Horseshoe Crab (Limulus polyphemus)
Photo: Kaldari, Wikimedia Commons (CC0)

What if it disappeared?

Impact High
Each year, United States

About 500,000 horseshoe crabs are bled each year for their blue blood, used in a test that detects bacteria in injectable drugs and medical equipment — up to a third of their blood volume is drawn, with mortality among released animals estimated at 15 to 30%.

Documented
Detail

Maloney, T., Phelan, R. et Simmons, N. (2018). Saving the horseshoe crab: A synthetic alternative to horseshoe crab blood for endotoxin detection. PLOS Biology, 16(10), e2006607.

A synthetic alternative, recombinant Factor C (rFC), has been commercially available since 2003 and has proven at least equivalent to the traditional test — arguably superior, since it avoids false positives caused by glucans present in the horseshoe-crab-blood test. Its adoption nonetheless remains limited across the pharmaceutical industry, despite the potential to replace up to 90% of current demand without requiring new regulatory approval.

Over 17 years, Delaware Bay

The harvest of horseshoe crabs for fishing bait increased 10-fold during the 1990s, causing a more than 90% drop in egg availability on spawning beaches — the red knot population that depends on those eggs to complete its migration declined by more than 75% over the same period.

Documented
Detail

Niles, L.J. et al. (2009). Effects of Horseshoe Crab Harvest in Delaware Bay on Red Knots: Are Harvest Restrictions Working? BioScience, 59(2), 153–164.

Horseshoe crab eggs, laid by the millions on Delaware Bay beaches each spring, are the concentrated food resource that lets several shorebird species rebuild fat reserves in just a few weeks before the final leg of their migration to the Arctic — a link so precisely timed and localized that these birds' survival depends directly on how the horseshoe crab fishery is managed.

Documentation

Last verified: August 14, 2026

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