How a Horseshoe Crab Saved My Life

Here in Delaware and along the Indian River Bay, is a favored breeding ground for a species that has survived for the last 450 million years.... the Horseshoe Crab. Chances are, if you have walked the area beaches over the years, you have likely come across one of these primordial sea creatures. These little ancient wonders of the sea have weird blood, peculiar swimming habits and a secret weapon that has probably even saved your life.




1. These guys are really old.

in 2008, the fossilized remains of a 1.5" wide lunataspis aurorua was discovered in Canada and predated the previous specimen by over 100,000 years. Nearly a half billion years later, there are four species still with us and can span up to nearly 20 inches. Limulus polyphemus is the only species found in North America.


2. Honestly...? They aren't even crabs

...and not to truly blow your mind, but technically, they're not even crustaceans. Real crabs have antennae, but that's not the case for the misclassified ocean dweller. They are officially chelicerates, a species subdivision of arachnids, like a spider or scorpion! The defining attributes are a multi-segmented body and pair of unique, pincer-like feeding appendages called chelicerae (thus the name).


3. Huge number of sight organs.

They have a total of ten eyes placed all over the body, including a pair under the shell called "ventral eyes", presumably to help it navigate while swimming and eating. The most obvious are the largest set located on the sides of the shell called "compound eyes". Did you know that a great deal of our understanding of how our eyes work is based on the study of this set of eyes on the horseshoe crab? Well me either! By virtue of the simplistic wiring of these eyes, scientist have learned a great deal. Now you have a little nugget of trivia to bewilder your friends at your next dinner party!


4. The babies swim upside down.

For the most part, horseshoe crabs get around as one might expect - crawling along the ocean floor. Nevertheless, young crabs flip themselves over and propel themselves through the water, using their gills as extra paddles. As they grow, they shy away from this technique and eventually travel upright like any self respecting horseshoe crab should.


5. Their spiked tails have several uses

...and contrary to what many believe, stinging is not one of them. This sharp appendage, called a telson, has given the arthropod a bad name and many consider it a dangerous animal although, in truth it's completely harmless (Now if you step on the tail, that's a different story, but hey- at 450 million years old, they pretty much were here first). The tail serves as a rudder of sorts and also helps them to right themselves when they are overturned. The tails of the young are much smaller in proportion and grow as they age.


6. The adults eat Bivalvia

Both larvae and adults eat aquatic worms. Adult horseshoe crabs also devour alga and carrion but primarily dine on Bivalvia, such as clams and mussels. When it comes time to eat, these low-profile predators mash food between the spiky upper regions of their legs before pushing it into their mouths.

7. Hundreds of thousands gather in the Delaware Bay for annual spawning

Every year in May and June, the bay becomes the largest Atlantic horseshoe crab zone on Earth. During the night, the females climb on shore with one or more males in tow. After digging a hole and depositing her eggs, the males fertilize them. This process repeats several times over tens of thousands of eggs. During this ritual, privacy and intimacy are thrown out the window. Beyond the spectators who come to witness this evening event, the crabs have to contend with migratory shore birds who feast on the nutrient-rich eggs during a final pit stop on their migration on their way to South America by way of the Arctic.


8. Not the greatest of lifespans

A mother can lay up to 90,000 eggs per clutch. Even with such a large number, it is estimated that only about ten of these embryos will ever reach adulthood. A devastating result for the horseshoe crab, but a vital part of survival for the ecosystem. Fish, sea turtles and birds rely heavily on the food source. The adults that do manage to survive, usually reach sexual maturity around ten years of age and live roughly into their early twenties. Yet another, more horrifying cause of death occurs when they become over turned and unable to right themselves. They either expire in the sun or become a buffet for other predators.


9. The females are inherently larger

This holds true primarily for the North American species where the females are normally 20-30% larger. Unlike us, the females mature slower than males, reaching an average of 16-17 inches in width, while the males tend to be only 14-15 inches.



10. If you're under 40 and have been vaccinated, thank a horseshoe crab

You don’t survive for 450 million years without learning a trick or two.

In the case of horseshoe crabs, one of those is developing blood with remarkable antibacterial properties. We as humans haven’t been around nearly as long, but it didn't take us long to figure out how to harness those properties in ways that save our lives. The most obvious and unusual property of their blood is that it is bright blue, a consequence of using copper-based hemocyanin to transport oxygen where vertebrates use iron in hemoglobin. Instead of white blood cells to fight infection, many invertebrates have amebocytes, and the Atlantic horseshoe crab has evolved to such a peak of refinement that they are of enormously valuable in the medical field. ​ Their amebocytes coagulate around as little as one part in a trillion of bacterial contamination. Even better, the reaction takes 45 minutes, not two days as with mammalian equivalents. Coagulan, the chemical that makes this possible, is used for testing medical equipment and vaccines prior to use, without which many more people would die from infections. Unfortunately, coagulan synthesis is in its infancy so a quarter of a million crabs are harvested each year for their blood. Good for us, not so much for the horseshoe crab.

On the world market, a quart of horseshoe crab blood has a price tag of an estimated $15,000, leading to overall revenues from the LAL industry estimated at U.S. $50 million per year (as of 2008). But don't get any ideas. You won't find crab blood harvesting equipment at your neighborhood hardware chain and trying to extract it on your own is huge No-No that could cost you more than the quart is worth.

So the next time you're strolling along the beach front and come across one of these creatures, remember your manners. ​ Treat the elderly with respect, flip them right side up, thank them for their sacrifice and let them enjoy what little life they have ahead of them.