Skip to main content

Why you owe a “thank you” to the horseshoe crab – its blood could save your life

If you’ve ever gotten a vaccine, or perhaps you or someone you know has taken an insulin shot or has a pacemaker implanted, you may have to thank the horseshoe crab for saving your life. Horseshoe crab blood contains a compound called Limulus Ambebocyte Lysate (LAL) which forms a gel-like clot in the presence of endotoxins released by gram-negative bacteria in concentrations as low as one part per trillion. Because of LAL’s sensitivity, the FDA requires LAL testing of all intravenous drugs and medical equipment (including needles, prosthetics, heart valves, and pacemakers, to name a few) for contamination.

Of course, LAL testing on this scale requires a lot of horseshoe crab blood, blood from approximately 500,000 horseshoe crabs per year to give you an idea. Adult horseshoe crabs are fished and transported to LAL labs, where they are bled to extract LAL. The horseshoe crabs are flexed at the joint as pictured below and have a needle inserted into their heart. Each crab is bled for about three minutes and up to 30% of the blood volume is removed. They are then returned to the water, far from where they were caught to avoid immediate recapture, and their blood volume returns to normal in about a week.The extracted blood is then centrifuged to isolate the amaebocytes and the coagulation is broken down to extract LAL, which is worth about $15,000 per quart.

Extraction of horseshoe crab blood for LAL. Photo: Andrew Tingle, Wired

Mortality from the bleeding is generally low at around 8-20% and can be reduced if external stressors related to handling and transport are minimized (Gerhart 2007). However, the blood loss can affect horseshoe crab populations. Researchers at the University of New Hampshire and Plymouth State University have found that recently bled horseshoe crabs have lower activity levels and decreased hemocyanin (copper-binding substance in their blood – basically their equivalent to iron-binding hemoglobin in our blood) levels that can alter immune function (Anderson et al. 2013). Bled horseshoe crabs can also become disoriented and have difficulty finding nesting beaches (Kurz and James-Pirri, 2002).

Although there have been efforts to create alternate tests for LAL, a few of which have shown promising results, nothing has gone to the level of FDA approval yet. This is troubling in light of horseshoe crab declines over the past few decades due to overfishing for the bait industry and loss of shoreline breeding habitat. Even more troubling is that throughout much of their range (like here in Florida), very little is known about their population structure and biology. Without horseshoe crabs and LAL, how can we ensure the safety and sterility of our medications and medical equipment?

So how can you help?

  • Sometimes horseshoe crabs that come up to the shoreline during high tide for breeding will get stranded on the beach as the tide goes back out. Although horseshoe crabs can survive on land for some time, extended exposure to high temperatures on the beach can kill them. If you see a horseshoe crab flipped over on its back, gently flip it back over and take it down to the water.
  • If you see any horseshoe crabs while you’re out on the beach, report your sighting to FWC here.
  • Get involved with the Horseshoe Crab Citizen Science program! UF/IFAS Nassau County Extension currently conducts beach surveys on Amelia Island and in northern Duval County with volunteers where we look for horseshoe crabs. All data is sent to FWC for development of a statewide Citizen Science program which will involve using trained volunteers to regularly monitor established transects and tag horseshoe crabs (we will start formal monitoring in NE Florida in Fall 2017). If you are interested in getting involved, contact me at (904)530-6356 or



Anderson, R. L., W. H. Watson III, C. C. Chabot. 2013. Sublethal behavior and physiological effects of the biomedical bleeding process on the American horseshoe crab, Limulus polyphemus. Neurobiology and Behavior 225(3): 137 – 151.

Gerhart, S. D. 2007. A review of the biology and management of horseshoe crabs, with emphasis on Florida populations. FWRI Technical Report TR-12. Florida Fish and Wildlife Conservation Commission. 31 pp.

Kurz, W., and M. J. James-Pirri. 2002. The impact of biomedical bleeding on horseshoe crab, Limulus polyphemus, movement patterns on Cape Cod, Massachusetts. Marine and Freshwater Behavior and Physiology 35(4): 261 – 268.