Horseshoe crab pets are among the most fascinating marine creatures you can add to your aquarium. Having a prehistoric appearance and an unusual role in aquatic ecosystems, they add curiosity and charm to saltwater tanks. From their ancient lineage to behavior and specific care needs, there is much to learn about these incredible animals.

In this guide, I will go over some important information about horseshoe crab pets, including their role in aquariums and their habitat needs.
Quick Overview of Horseshoe Crab Pet
- Common names: American horseshoe crab, Atlantic horseshoe crab
- Scientific name: Limulus polyphemus
- Care level: Moderate
- Temperature: 59-69.8°F (15-21°C)
- Temperament: Peaceful
- Color: Brownish-green with a hard, dome-shaped shell
- Size: 7-18 inches (including tail spine)
- Diet: Omnivore (scavenger)
- Habitat type: Large saltwater aquarium
- Sleeping nature: Nocturnal
Fun Facts About Horseshoe Crab Pets
The horseshoe pet crab is an exceptional creature that traces back to over 450 million years ago, making them living fossils. Although they may look like aliens from another planet, they are docile scavengers, very important in marine ecosystems and even aquariums. Keeping horseshoe crab as a pet could be both fascinating and educational. Here are some horseshoe crab fun facts:
Habitat and Distribution
Native to coastal areas and shallow waters, horseshoe crabs are especially found along the Atlantic coast of North America and Southeast Asia. They like sandy or muddy substrates where they can burrow and forage for food. In captivity, they need a large saltwater tank with a soft sand bottom to mimic their natural environment.
Horseshoe Crab Behavior
Horseshoe crabs are primarily nocturnal, becoming active at night to scavenge for food on the ocean floor. Horseshoe crabs are also non-aggressive and spend most of their time digging or foraging among the sand and silt for organic debris and small invertebrates. These crabs are natural cleaners of the tank and help to maintain an aquarium environment that is healthier by consuming the remaining food and waste.
Appearance
These crabs obtain their name from their hard, dome-shaped shell curved in a horseshoe shape. Normally, pet horseshoe crabs are brown-green colored, and it comes rather helpful in camouflaging them from their ocean bottoms. Their sizes range anywhere between 7 to 19 inches, containing a long tail spine or telson. They do possess a multitude of eyes on their shell and tail, using them to detect the presence of light and action.
Horseshoe Crab Blood
Horseshoe crab blood is blue, which includes copper-based hemocyanin. It contains unique amebocytes that are crucial in the detection of bacterial contamination in medical applications. Such remarkable blood has revolutionized pharmaceutical safety and keeps vaccines and medical devices free from harmful toxins.
About Their Unique Shell
The shell of the horseshoe crab pet is for protection and hydrodynamics, serving them to move efficiently in the water. In contrast to other kinds of crabs, like red emerald crabs, thin-striped hermit crabs, or strawberry crabs, the tail spine of the horseshoe crab does not serve as a weapon but helps to flip them over onto their back when they end up on it. This is one peculiar adaptation that differentiates them from all other crab species.
Mating and Breeding of Horseshoe Crabs
Horseshoe crab mating behavior is an extraordinary natural process wherein, during spawning, males clasp onto females with their special claws in the sand on beaches. Females lay eggs in burrows and then are externally fertilized by males to ensure breeding success in a coastal environment.
Horseshoe Crabs Lifespan
Horseshoe crabs are long-lived animals, living up to 20 to 40 years in the wild. Answering how long a horseshoe crab lives depends on stable habitats, minimal predation, and their ability to molt and grow over time.
Are Horseshoe Crabs Reef Safe?
Horseshoe crabs are generally described as reef-safe because they pose no danger directly to the corals or other reef organisms. However, this natural tendency of theirs to dig into the substrate might cause unconscious disturbances.
Digging could potentially uproot corals or dislodge delicate fragments, thus clouding the water with sediment. While smaller horseshoe crabs may acclimate well in a reef tank and coexist with other animals, growth can make them a disruptive force.
Their sandbed foraging habits will eventually increase with age and accidentally damage the stability of a reef environment, potentially disrupting other invertebrates. Therefore, they are generally not considered a good choice for most reef systems.
Can You Have Horseshoe Crab as a Pet?
To the question “Can I keep a horseshoe crab as a pet?” These animals are better found in large marine tanks with a sandy bottom to replicate natural burrowing behaviors. Their care is complicated, entailing stable salinity and temperature with frequent monitoring. Hence, they are more suitable for advanced aquarists than for casual owners.
How Can You Keep a Horseshoe Crab as a Pet?
Raising horseshoe crabs in captivity is no ordinary undertaking. These prehistoric animals require the most meticulous care and a well-thought-out habitat to survive in captivity. For those enthusiasts who ask, “Can you have a horseshoe crab as a pet?” or “Can horseshoe crabs be pets?” the answer is yes but only if you are ready to commit to their specific needs.
Here’s a detailed guide about how to take care of horseshoe crabs as pets to ensure their well-being:
Designing the Perfect Saltwater Tank
Horseshoe crabs need a lot of space to grow and to provide them with conditions close to their natural habitat.
- Tank Size: A minimum of 180 gallons is necessary, especially when considering that these animals can reach up to a foot in diameter.
- Substrate: Use fine sand as the substrate in the bottom of the tank so they are allowed to burrow as they would naturally do and act the same.
Perfecting Water Quality and Stability
The horseshoe crabs are sensitive to water conditions; thus, the need for regular maintenance.
- Salinity: Maintained between 20–35 ppt (parts per thousand).
- Temperature: Keep the water temperature between 59-69.8°F (15-21°C) to simulate their natural coastal environments.
- Filtration System: Use a good filtration system to supply clean, well-oxygenated water.
Feeding Your Horseshoe Crab Pet
In respect to their diet, one might ask, “What do pet horseshoe crabs eat?” Bottom feeders are things that require a broad diet to keep themselves healthy and thriving. In the wild, horseshoe crabs feed on small mollusks, worms, algae, and other organic matter in the sediment. They will do great as pets on a diet that can replicate their natural food. Some suitable foods include:
- Marine Worms & Bristle Worms
- Small Shellfish (Shrimp & Clams)
- Fish & Squid Pieces
- Algae & Organic Debris
Managing Growth and Molting
Horseshoe crabs grow by molting, a process in which they shed their exoskeleton.
- Space for Growth: Make sure your tank is big enough to accommodate their increasing size.
- Comfort Zone: Avoid congestion or sudden changes in water conditions, as these may affect their molting process.
Avoiding Overcrowding
Horseshoe crabs are solitary animals and do best in tanks that are relatively free of distractions.
- Tank mates: If you wish to add other species, use peaceful, non-aggressive tank mates that will not harass or stress the horseshoe crab.
Here is a video where you can see this pet crab:
Frequently Asked Questions
Can you keep horseshoe crabs as a pet?
Yes, you can keep horseshoe crabs as pets, but they need experienced care, large saltwater tanks, and maintained water parameters in terms of salinity and temperature for them to live and grow.
Can horseshoe crabs be kept in captivity?
While horseshoe crabs can be kept in captivity, the care of such animals requires specialized knowledge. They must be kept in a large tank with stable water conditions, including an appropriate sandy substrate for their ground habitat.
Is it legal to have a horseshoe crab pet?
Most places will have it legal to keep horseshoe crabs, but regulations can exist regarding their collection or ownership, especially concerning endangered species.
Are horseshoe crabs friendly?
Horseshoe crabs are totally harmless to humans. They do not have the ability to bite, and their claws are so gentle, and their grip is so weak that they are absolutely safe to handle.
How do you take care of a horseshoe crab in a fish tank?
Care for a horseshoe crab in a fish tank by having a sandy substrate for burrowing, water salinity between 20-35 ppt, and a temperature range of 59-69.8°F (15-21°C). Regular water changes and a high-quality filtration system are also important in maintaining the best conditions.
Why are horseshoe crabs so cool?
Horseshoe crabs are cool because of their ancient lineage, unique exoskeleton, long tail spine, complex mating rituals, and role in marine ecosystems. Their blue blood is also crucial for bacterial endotoxin testing in research.