All About Horseshoe Crabs: The Living Fossils

Horseshoe crabs are one of the most primitive living creatures on Earth. They are essentially unchanged from when they first appeared in the fossil record 450 million years ago, which is why they’ve been called “living fossils.”

The horseshoe crab is not a fish at all but an arthropod that has evolved over time to be more like a shellfish, or in other words, it has become what we call a “limbless crustacean.” Enough of that, though! Let's move on to what makes the living fossils such beautiful animals!

Description and Appearance

The horseshoe crab’s body is a deep blue-black and they have a hard shell that covers their back. They have two large, compound eyes on the top of their head and ten smaller eyes along the edge of their shell. They also have two pairs of antennae, one pair of which is used to feel around for food. Their sea-dwelling cousins are able to spray a bright green substance out of their tails, which they use for both defense and attracting mates.

The living fossils have ten legs with tiny claws on the ends, and they use six pairs of them to walk around and dig for food in sand or mud at the bottom of the ocean. They are shy, gentle creature that mainly eats small crustaceans and worms. To add to being shy and gentle, they’re amazingly fluffy, too—at least their plushie alternatives, that is! Gage Beasley’s Horseshoe Crab Soft Stuffed Plush Toy isn’t a living fossil, but it could knock the life out of you to bed. It’s cute, cuddly, and very realistic.

Gage Beasley’s Horseshoe Crab Soft Stuffed Plush Toy

They can grow up to 18 inches long (46 cm) and can weigh up to 6 pounds (2.7 kg). As you can see, they are not large creatures, but their unique features and long history make them one of the most fascinating animals on Earth.


The horseshoe crabs' diet consists of small invertebrates such as worms and mollusks, but they will eat almost anything. They can often be found in tidal flats, digging with their legs for small crustaceans to eat.  They also like to eat jellyfish, plankton, leaves, and even garbage. They will also scavenge on dead things they find on the ocean floor. Occasionally, they will eat leaves that fall off of trees near the water's edge.

The horseshoe crab has a small mouth in its belly, so it cannot eat big things. That is why it eats many small things instead of one large thing.

Despite the horseshoe crab having gills, it does not breathe underwater. It breathes air through its book gills. The respiratory current created by the book lungs is also used to move food towards the mouth. This gives the impression that they are eating constantly, which is why their mouths are permanently open. The horseshoe crabs are even able to breathe when walking underwater.


Reproduction in horseshoe crabs is a unique process that has remained unchanged for more than 450 million years. Female horseshoe crabs lay eggs on the beach, and the males fertilize them externally. The embryos develop into larvae, which eventually find their way back to the sea.

The larvae are tiny versions of the adults and have a long, pointed tail. They use this to swim around in search of a place to settle down. When they find a suitable spot, they use their claws to dig into the sand and bury themselves.

After a few weeks, the larvae transform into adult horseshoe crabs. They emerge from the sand and start the process all over again by laying eggs on the beach.

Distribution and Conservation Status

The horseshoe crab is found in the eastern Atlantic Ocean and the Mediterranean Sea. They are also common in the Gulf of Mexico and along the East Coast of the United States. In these areas, they inhabit coastal waters near beaches and estuaries.

Horseshoe crabs have been around for over 450 million years and are one of the oldest species alive today. They are not actually crabs but more closely related to spiders, scorpions, and other arachnids. Since their height is below the water level while they're resting on the seabed or shallow areas, it's hard for humans to tell whether they are extinct or not by just looking at them.

Horseshoe crabs are currently in the "Least Concern" category in the IUCN red list, meaning that there is not sufficient information about them to determine if they are in danger of extinction. However, this class was given to them when only two populations were known. Recent discoveries have shown that there are more populations than previously thought, though they are still limited in number.

One of the biggest threats to horseshoe crabs is habitat loss. Coastal areas in which these creatures live are subject to many disturbances including storms, flooding, erosion, changes in salinity amounts due to large ships passing through channels where freshwater mixes with saltwater and dredging for development.

In addition to habitat loss, degradation can also be a threat. Horseshoe crabs depend on healthy ecosystems in order to survive. When their environment is polluted or disturbed in some way, it becomes difficult for them to live and reproduce successfully.

Another threat to horseshoe crabs is overharvesting. They are often caught and used for bait, primarily in the crab and lobster fishing industry. They are also used in medical research and as fertilizer.

The demand for horseshoe crabs is high, and so their population has been declining in recent years. In order to ensure that they don't become extinct, the harvesting of horseshoe crabs must be regulated.

Horseshoe crabs are also prized for their blood. It contains a protein called Limulus amebocyte lysate (LAL), which is used to test for bacteria in pharmaceuticals and medical devices. As a result, horseshoe crab populations have been declining, and they are now considered an endangered species.

So what can be done to help protect these ancient creatures? One solution is to create marine sanctuaries where horseshoe crabs can be protected and allowed to thrive. Another solution is to find alternative sources of LAL so that the demand for horseshoe crab blood can be reduced.

One way to protect them is by restricting fishing vessels in certain areas during their breeding season. The adult population needs time to mate and lay eggs without interruption, so this regulation would allow them enough time to breed successfully.

Unsustainable tourism could also pose a threat to horseshoe crabs. When people visit areas where they live, it can be disruptive and cause them to leave the area. This could lead to a decline in their population over time.

In order to help protect this species, it's important to be aware of the threats they face and do what we can to reduce them. We can all play a role in conserving horseshoe crabs by choosing to not harvest them, volunteering with local conservation groups, and spreading awareness about their importance.


The horseshoe crab is a very unique animal with many facts and things to learn about them. One of the most interesting facts about it is that its blood is used in medical procedures because of its clotting ability. Not only are they fascinating animals but they are also related to spiders, scorpions, ticks, mites, and other arachnids.

Despite their ancient origins, horseshoe crabs are still an important part of the marine ecosystem. They play a crucial role in the ocean’s food chain by scavenging dead animals and fish on the seafloor. They are also a source of food for many different species of birds and marine animals.

They are truly living fossils and provide a lot of information on the evolutionary process. As more research is conducted on them, scientists are able to learn even more about their biology and ecology. They are definitely an interesting creature worth studying!

Overall, the horseshoe crab is a very unique and interesting animal that many people don't even realize exists. It's great how it has been around for millions of years and continues to survive today.



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