Horseshoe Crab Preservation
Horseshoe crabs are frequently seen on the beaches of Cumberland Island. These intriguing animals are usually about 18 inches long and look like an old metal helmet with a tail. They stay primarily on the ocean floor, feeding on mollusks, worms and seaweed. They use their 10 eyes (!!) to find mates and sense light as they navigate along the ocean floor.
While they might have a startling appearance, they are one of the most harmless creatures on the seashore. They cannot bite or sting, and their barbed tail is used to move through sediment, as a rudder and to right itself if it tips over.
But did you know that most horseshoe crabs do not even make it to the larval stage before being eaten? Some migratory shorebirds, including the red knot, rely on horseshoe crab eggs to survive. Fish and sea turtles are also known to feast on the eggs of the horseshoe crab.
If an egg does survive, it will spend the next 10 years or so molting and growing. You can tell a molt from a dead crab by how hard the shell is. A molt that has been left behind will be flexible and can crack if pressed too hard.
If you look carefully at the rounded front end of the molt, you’ll see where the top and the bottom have separated to allow the horseshoe crab to crawl out of the old exoskeleton, leaving it behind.
Finally, it will be able to reproduce, and during late spring and early summer, adult horseshoe crabs travel from deep ocean waters to beaches along the East and Gulf coasts to breed. Males, usually about two thirds the size of their mates, will cluster along the water’s edge and await the arrival of the females on the shore.
Males have ‘glove-like’ claws on the first pair of their legs which they use to hang onto the females’ shells. Females make their way to the high tide line with the males hanging onto their backs. Once the female reaches the high tide line, she pauses every few feet to dig a hole and deposit as many as 20,000 pearly green birdshot-sized eggs. The male on the female’s back fertilizes the eggs as he is pulled over the nest. After the spawning is complete, the crabs leave and the eggs are covered with sand as the waves wash over them.
Wild Cumberland is proud to support the efforts of the Horseshoe Crab Recovery Coalition, which was established to ensure that this species doesn’t just survive — it thrives.
What You Can Do:
- Though they can survive for a short time if their gills remain wet, a hot sunny day can dry out and kill an upside-down horseshoe crab quickly. Don’t be afraid to help! Gently pick it up by the sides of its shell (not by its tail) and put it back at the edge of the water.
- Watch where you dig! Horseshoe crab eggs are tiny, green spheres, laid near the surface of the sand. Know how to recognize them: if you see them washed up on the shore, leave them alone so that hungry shorebirds can eat.
- Always fill any holes in the sand before you leave as horseshoe crabs can easily become trapped in holes left in the sand.
Learn More
Learn more about these animals, which are most closely related to spiders and predate the dinosaurs.
Horseshoe Crab Facts
- They may resemble a crab, but they are actually more closely related to the spider or scorpion.
- Horseshoe crabs have a total of 10 eyes used for finding mates and sensing light.
- Horseshoe crabs can even swim upside down in the ocean using their dozen legs (most with claws) and a flap hiding nearly 200 flattened gills.
- The Delaware Bay region is home to the largest population of the Atlantic horseshoe crab (Limulus polyphemus), which is found along US shores from Maine to Florida, and expanding as far west as Texas.
- Horseshoe crabs stay primarily on the ocean floor, feeding on mollusks, worms, and seaweed. In the winter, they burrow into the sediment.
- They are one of the most harmless creatures on the seashore. They cannot bite or sting, and their barbed tail is used to move through sediment, as a rudder, and to right itself if it tips over.
- The horseshoe crab doesn’t have an internal skeleton. Its chitin shell serves as an exoskeleton, providing structure and protection.
- Males are only two-thirds the size of their mates.
- Males cluster along the water’s edge as females arrive on shore. Using ‘glove-like’ claws on his first pair of legs, the male hangs on to the female’s shell and is pulled up the beach to the high tide line.
- The female then pauses every few feet to dig a hole and deposit as many as 20,000 pearly green, birdshot-sized eggs. The male fertilizes the eggs as he is pulled over the nest. After the spawning is complete, the crabs leave and the waves wash sand over the nest.
- Horseshoe crabs molt until they are about 10 years old.
- This “living fossil” plays an important role in modern medicine. Its blood — which is blue because it contains copper instead of iron — contains Limulus Amebocyte Lysate (LAL), which is used by the Federal Drug Administration for medications and vaccines. It is also used to make products such as bait, fertilizers, hairspray, and contact lenses.
- In the United States, horseshoe crabs are found up and down the Eastern Seaboard.
- Overharvesting and coastal habitat destruction are causing a decline of its population in the Atlantic.
- The Atlantic horseshoe crab is listed as “vulnerable to extinction” on the IUCN Red List of Threatened Species.