The Horseshoe Crab – A Relic Prince of the Blue Bloods: Habitat, Dangerousness, and Interesting Facts

Nature is incredibly unpredictable. Some of its creations are so familiar to humans that they evoke no feelings, while others inspire delight, admiration, or, conversely, disgust. But among them are those that seem like aliens from other worlds, accidentally landing on our planet. For example, horseshoe crabs – relic creatures that have preserved their primordial form despite millions of years of evolution.

It seems that time has no power over them: these ancient animals appeared even before the era of dinosaurs and continue to exist to this day. Scientists estimate their age to be 350-450 million years old.

Who is the Horseshoe Crab?

1. Horseshoe crabs, or “limulus crabs,” are the closest relatives of ancient trilobites and, according to modern classification, belong to the order of aquatic chelicerates of the class Merostomata.
2. They can be easily recognized by their characteristic features – a long and pointed tail spine and a massive shield-like carapace.
3. Their body shape resembles a slightly flattened drop consisting of two separate mobile segments – the prosoma and the opisthosoma.
4. “Limulus crabs” can reach sizes of 50-90 cm depending on the species to which the individual belongs.
5. They have a greenish-gray color, allowing them to successfully camouflage themselves by burying themselves in mud or sand.
6. Only their chitinous carapace remains on the surface, resembling a horse’s hoof carelessly thrown on the shore.

Blue Blood

1. The blood of horseshoe crabs is not red but blue, which is due to a high copper content.
2. Humans have learned to use this characteristic of relic animals to their advantage: individuals are caught, and a certain amount of bodily fluid is extracted and then released to recover.
3. The substance obtained in this way is used to test medical preparations for sterility and is currently used to create experimental vaccines against the coronavirus.
4. The blue blood of horseshoe crabs is truly unique: if even the smallest amount of “bad” bacteria or other foreign microorganisms gets into it, it immediately coagulates and turns into jelly. This is how the immune system of the horseshoe crab works, protecting other organs from infection.
5. Every year, about half a million horseshoe crabs are caught in water bodies and sent to laboratories.
6. Horseshoe crab blood is highly valued – one liter of reagent obtained from horseshoe crab hemolymph costs almost $15,000.

When Did Horseshoe Crabs Appear?

1. It is believed that the first representatives of these animals appeared in the Paleozoic era, 450 million years ago.
2. They managed to survive many natural disasters and global catastrophes.
3. However, due to the destructive influence of humans, the population of these animals has significantly decreased – out of numerous species (over a hundred), only four have survived to this day.

What Do Horseshoe Crabs Eat?

1. The menu of the “limulus crab” is very diverse – it eats anything it can find.
2. Crawling in the mud, it searches for roe, larvae, worms, mollusks, or snails.
3. As soon as the prey comes into its sight, the horseshoe crab attacks it with its tail or front limbs, ending in claws.
4. Then it tears the captured prey into small pieces and puts them in its mouth.
5. Over such a long period of existence, horseshoe crabs never developed teeth, so they still feed in this barbaric way.
6. If a horseshoe crab is unlucky in hunting, it can also feed on carrion.
7. It will definitely not stay hungry, as even algae will suffice – horseshoe crabs are omnivorous.

Habitat

1. Horseshoe crabs live exclusively in warm water, choosing places where the average annual temperature does not drop below 20°C.
2. Horseshoe crabs are not very good swimmers, so they settle near the shores, at depths not exceeding 35-40 meters.
3. They feel very comfortable on the shelves, in the shallows, and other rocky areas.
4. They are less commonly found in the mouths of large rivers, as fresh water is not a hindrance to them.
5. The geographical range of horseshoe crab habitats includes the shores of South and Central America, the Bay of Bengal, Southeast Asia, the islands of Indonesia, the Philippines, Japan, and Borneo.

Danger to Humans

1. Horseshoe crabs do not attack humans. However, they cannot be called harmless either, mainly due to the risk of injury.
2. The horseshoe crab will not intentionally sting with its sharp spiky tail, but there is a chance of not noticing an individual lurking in the sand and stepping on it with a bare foot.
3. Most likely, this will result in a deep wound, and there will be a risk of infection. In this, the horseshoe crab is similar to the stingray.
4. Horseshoe crabs should not be feared, but one should handle them carefully.
5. Especially since humans are much more dangerous to horseshoe crabs than vice versa.
6. Those who want to take a cool photo or just curious tourists, upon seeing the relic animal, tend to hold it in their hands. Because of the spikes on the carapace, individuals are usually grabbed by the tail, causing pain and injuries.

Is the Horseshoe Crab Venomous?

1. Contrary to the fears of many travelers encountering horseshoe crabs for the first time, there is no venom in their long, sharp tail.
2. However, young individuals of mangrove horseshoe crabs contain toxins in their bodies that can lead to rapid lethal outcomes if their meat is consumed without prior heat treatment.
3. Horseshoe crabs are served in Vietnam, China, Japan, and some other regions.
4. It is not worth trying this exotic dish if you are not confident in the chef’s qualifications.

Interesting Facts About Horseshoe Crabs

1. Anatomically, horseshoe crabs are more similar to scorpions and spiders than to crabs.
2. Sometimes you can hear another, third, name for these relic animals – “multi-eyed.” The point is that they have additional pairs of eyes, located on the sides and capable of detecting the slightest movement around, which greatly facilitates the search for food.
3. The horseshoe crab swims belly up, using its own carapace as a raft. And the spiky tail serves as a kind of balance.
4. During the breeding season, a mass gathering of individuals on beaches can be observed. Spawning is the only reason that ancient animals unite in groups and leave their accustomed places on the seabed or ocean floor.
5. After mating, females can lay up to 1000 eggs, which resemble caviar.
6. Enthusiasts of exoticism keep horseshoe crabs in aquariums as pets.
7. They do not require much care; it is enough to simply maintain cleanliness and saturate the water with oxygen.
8. Raw meat or even boiled sausage will be suitable as food for these relic princes.