5 Reasons Horseshoe Crabs are Cool Creatures

Horseshoe crabs can be found on many beaches along the Jersey shore.  Their coolness factor? Don’t be so quick to judge.

Honestly, they get a bad wrap.  Where are their eyes?  Wait, how many eyes do they have?  That hard shell and tail don’t attract people to think of them as cute, cool or helpful creatures from the sea.  Helpful?  We’ll explain.

1. Horseshoe crabs aren’t really crabs.

They’re not crabs at all but more closely-related to spiders.

2. Here’s “looking” at you kid…


Rachel Oh via Wikimedia Commons

Each horseshoe crab has an array of sight organs.  Large compound eyes rest on the sides of their shells. Come mating season, these bean-shaped units help crabs locate a partner. Behind each one, there’s a small, primitive photoreceptor called a lateral eye. Towards the front of the shell are two tiny median eyes and a single endoparietal eye. On its underside, a horseshoe has two “ventral eyes,” which presumably help it navigate while swimming.

2. They’re kind of dinosaurs.

And you thought Jurassic Park was the only way to see dinosaurs in 2016?  Nope.  Aside from the potential for raptors and T-Rex returning, horseshoe crabs can claim “dino-status” in the here and now. They are actually considered dinosaurs – yes, dinosaurs!  These “living fossils” have been around for 445 million years.  Discovered in 2008, the 25 millimeter-wide Lunataspis aurora crawled over Manitoba nearly half a billion years ago, about 100 million years older than any previously known forms.  This makes it the world’s oldest-known horseshoe crab. Four species are with us today, all of which closely resemble their long-extinct ancestors.


3. Hundreds of THOUSANDS Gather in the Delaware Bay for a Massive Breeding Frenzy.

Every year in May and June, the Delaware bay becomes the largest Atlantic horseshoe crab spawning zone on EARTH. During the night, a female will climb ashore with a male (or several) in hot pursuit. After she digs a hole and deposits her eggs, the males fertilize them. Migratory shore birds descend upon the bay in huge numbers to feed on the nutrient-rich eggs. Scores of red knots, which use the crab fest as a final stop during their yearly migration from the Arctic to South America making it a great spot for bird watching fans.

4. Adulting is super hard for a horseshoe crab.

Or making it into adulthood, anyway.  A mother can lay as many as 90,000 eggs per clutch. It’s estimated that only about 10 of those individual embryos will ever become adults. Before they get a chance to hatch, fish, sea turtles and birds consume the eggs making nesting horseshoe crabs vital to the ecology of Delaware Bay and countless other regions around the world.

5. Horseshoe crabs have been helping humans for 60 years. 


So sweet of them, huh?  Seriously, if you are under the age 0f 40 and have been vaccinated – thank the nearest horseshoe crab you can find.  Let us explain why.

A horseshoe crab’s blood is blue and contains hemocyanin, which contains copper, to transport oxygen throughout the body and turns bluish-green when it oxidizes.

(Our blood uses iron-based hemoglobin and turns red, as you most likely are aware, when exposed to oxygen.)


Another interesting fact about these anthropods is they lack infection-fighting white blood cells.  When you live in the sea and a single gram of undersea sediment contains roughly 1 billion bacteria, what do you do to fight infection?  Special cells called amebocytes attack pathogens in the horseshoe crab’s body by sealing them inside a gooey physical barrier, thus halting the spread of infection.

In 1956, Johns Hopkins University physician Frederick Bang discovered this characteristic leading medical researchers to test the safety of a vaccine or injectable drug by introducing horseshoe crab amebocytes into a sample.  If the cells start releasing their goo, it’s because they’ve encountered bacteria and the product isn’t ready for humans.

In the 1970s, the FDA made this test mandatory for experimental drugs and surgical implants.  The magic elixir is extracted from over 600,000 “donors” every year, each of whom parts with 30 percent of its blood before being released within 48 hours. Sadly, about 10–15 percent of captured crabs die somewhere in the process, and survivors can exhibit lethargic behavior down the road. Scientists aren’t insensitive to this problem.  Researchers have been trying to develop synthetic amebocytes and regulations have been set for blood extraction to ease impact on the species.

So there you have it. Horseshoe crabs are pretty awesome – don’t you agree?

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