15 Fascinating Facts About the Japanese Spider Crab

15 Fascinating Facts About the Japanese Spider Crab

Crustaceans are a diverse group of aquatic invertebrates that include lobsters, shrimp, and barnacles. Crabs are a particularly unique type of crustacean, with their distinctive hard shells and ten legs.

There are over 6,000 species of crabs found all over the world, in both saltwater and freshwater habitats. Some crab species include the Hermit crab, the Cancer pagurus, and the Dungeness crab among many others.

One of the most fascinating species of crab is the Japanese spider crab (Macrocheira kaempferi). The Japanese spider crab is found in the deep waters off the coast of Japan, at depths of up to 2,000 feet (610 meters).

It has a rounded body covered with stubby projections and long slim legs. The crab’s carapace (shell) is covered in a thick layer of spines, which helps to protect it from predators.

Even beyond its physical appearance, the Japanese spider crab is a fascinating creature. This article will highlight some of the most fascinating facts about this curious creature.

1. The Japanese Spider Crab Has the Largest Legs Among Arthropods

Internet Archive Book Images, No restrictions, via Wikimedia Commons

One of the most notable features of the Japanese Spider Crab is its massive legs. The Japanese spider crab has the longest legs of any arthropod, with a leg span that can reach up to 12.5 feet (3.8 meters).

However, it is important to note that the Japanese spider crab is not the largest arthropod or crab in the world. The coconut crab (Birgus latro) is the largest crab, with a body that can grow up to 1 foot (0.3 meters) in length.

The American lobster (Homarus americanus) is the largest arthropod in the world by mass, with individuals that can weigh up to 44 pounds (20 kilograms).

According to the Guinness World Records, a Japanese Spider crab known as “Big Daddy” holds the record for the longest leg on a crab ever. It measured 1.43 m (4 ft 8.5 in). Big Daddy lived at Sea Life Blackpool, UK, arriving from Japan in 2013.

2. Male Japanese Spider Crabs Are Usually Larger With Bigger Claws

Takashi Hososhima from Tokyo, Japan, CC BY-SA 2.0, via Wikimedia Commons

Male Japanese spider crabs are typically larger than female Japanese spider crabs, with bigger claws. This is a common feature in many animals.

In the case of Japanese spider crabs, the larger size and bigger claws, called chelipeds, of males are also used to compete for mates.

The males with the largest size and claws are usually the most successful at breeding. The bigger size is also helpful in fending off predators.

3. They Molt to Grow

Japanese spider crabs molt to grow, just like all other crabs and other crustaceans. Molting is the process of shedding the exoskeleton, or outer shell, in order to grow a new and larger one.

The molting process is complex and can take up to several weeks to complete. Here is a detailed description of the molting process in Japanese spider crabs:

1. The crab begins to produce a new exoskeleton underneath its old one.
2. The crab’s old exoskeleton begins to split at the seams.
3. The crab backs out of its old exoskeleton, starting with its legs and then its body.
4. The new exoskeleton is soft and vulnerable, so the crab must hide until it hardens.
5. The hardening process can take several weeks.

During the molting process, the crab is very vulnerable to predators. It is also unable to eat or drink, so it must rely on its stored energy reserves.

4. There’s A Limit To How Large They Can Get

H. Zell, CC BY-SA 3.0, via Wikimedia Commons

Interestingly, despite their large stature, there is a limit to how large the Japanese spider crab can get. This is due to a number of factors, including the availability of food and the presence of predators.

However, the main hindrance is the crab’s own biology. As crabs grow larger, their exoskeletons, that is carapace or hard upper shell, become thicker and heavier.

This therefore puts a cap on the crab’s size once it reaches adulthood. However, since the carapace is not on the legs, they keep elongating and growing to great sizes as seen above.

5. Japanese Spider Crabs Like to Play Dress-Up

Gzen92, CC BY-SA 4.0, via Wikimedia Commons

The Japanese spider crab is a type of decorator crab. Decorator crabs are a group of crabs that adorn their shells with sponges, algae, and other marine life.

This behavior is called decoration, and it is thought to serve a number of purposes, including camouflage, protection from predators, and communication.

Japanese spider crabs use a variety of materials to decorate their shells, including sponges, algae, hydroids, and other small animals. They attach these materials to their shells using their legs and claws.

Japanese spider crabs can change their decorations frequently, and they often create different patterns and designs.

6. They Fertilize Their Eggs Internally

The Japanese spider crab fertilizes its eggs internally through a process called internal fertilization. This process involves the transfer of sperm from the male crab to the female crab’s body, where it fertilizes the eggs.

The Japanese spider crab has a unique reproductive system that is adapted for internal fertilization. The male crab has two long appendages called gonopods, which are located on the underside of his abdomen.

The gonopods are used to transfer sperm from the male crab to the female crab during mating.

To mate, the male crab climbs onto the back of the female crab and positions his gonopods near her genital opening. The male crab then releases sperm into the female crab’s body through its gonopods.

The female crab can store the sperm in her body for several months before fertilizing her eggs. This allows her to mate once and then fertilize her eggs at a later time when the conditions are more favorable.

7. Female Japanese spider crabs have “aprons”

Dorieo, Public domain, via Wikimedia Commons

Female Japanese spider crabs have a unique feature known as an “apron”. This is not an apron in the traditional sense, but rather a flap of modified abdominal pleopods that is located under the crab’s abdomen.

The apron is used to store and protect the crab’s eggs. The apron is found on the underside of the crab’s abdomen, and it is made up of a series of overlapping plates.

These plates are covered in fine hairs that help to keep the eggs safe. The apron is a very important feature for female Japanese spider crabs.

It allows them to carry their eggs with them wherever they go, and it protects the eggs from predators and other hazards.

8. They Lay Up To 1.5 Million Eggs

Japanese spider crabs lay up to 1.5 million eggs in a single batch. After fertilization, The eggs hatch in the apron after about 10 days.

The larvae are called zoea, and they are planktonic, meaning that they drift freely in the water. The zoea larvae go through several molts before they develop into juvenile crabs.

The juvenile crabs then leave the apron and settle on the bottom of the ocean. Japanese spider crabs lay so many eggs because only a small fraction of them will survive to adulthood.

Many of the eggs will be eaten by predators, and others will die due to environmental factors such as disease and pollution. A large number of eggs ensures that at least some of them will survive to adulthood and reproduce.

9. Japanese Spider Crabs Go Through a Larval Stage Before Adulthood

Lycaon (Hans Hillewaert), CC BY-SA 3.0, via Wikimedia Commons

Japanese spider crabs go through a larval stage before adulthood. This stage is called the zoeal stage, and it consists of four substages.

During the zoeal stage, Japanese spider crabs are very different from their adult counterparts. They are much smaller, with a transparent body and long, slender legs.

Japanese spider crabs spend the first few weeks of their lives in the zoeal stage. During this time, they float freely in the water and eat plankton.

They also undergo a series of molts, or shedding of their exoskeleton, as they grow. After the fourth zoeal stage, Japanese spider crabs enter the megalopa stage.

This stage is a transition stage between the larval and adult stages. Megalopa crabs are larger than zoeal crabs and have a more crab-like appearance. They also have claws and walking legs.

Megalopa crabs spend several months in the megalopa stage. During this time, they settle to the bottom of the ocean and begin to feed on small animals. They also undergo one final molt before reaching adulthood.

10. Their Legs Can Regenerate

The Japanese spider crab is a fascinating creature, and one of its most remarkable features is its ability to regenerate its legs. When a crab loses a leg, it can grow a new one in its place.

This process is called molting, and it occurs periodically throughout the crab’s life. The new legs begin to form as small buds on the crab’s body.

These buds grow and develop over time, and eventually, they harden into new legs. The horseshoe crab is another crustacean that can regenerate its limbs.

11. The Japanese Spider Crab Is A Scavenger

Bjoertvedt, CC BY-SA 3.0, via Wikimedia Commons

The Japanese spider crab is an omnivore, so it eats both plants and animals. Its diet includes algae, detritus, and small animals such as crabs, shrimp, and mollusks.

However, it is also a known scavenger, meaning that it feeds on dead or decaying matter. The Japanese spider crab plays an important role in the marine ecosystem as a scavenger.

It helps to clean up the ocean floor and remove dead or decaying matter. This helps to keep the ocean healthy and prevents the spread of disease.

12. They Are a Culinary Delicacy

Wilford Peloquin, CC BY 2.0, via Wikimedia Commons

The Japanese spider crab, also known as the giant Japanese crab, is a culinary delicacy in Japan and other parts of Asia. It is prized for its sweet and delicate meat.

The crab can be prepared in a variety of ways, but it is most commonly served as sashimi or sushi. The crab is also sometimes used in soups, stews, and other dishes.

Here are some traditional Japanese foods you should try!

13. Japanese Spider Crabs Live In Deep Waters But Mate In Shallow Waters

Japanese spider crabs are fascinating creatures. They are one of the few creatures that migrate from deep waters to shallow waters to mate.

Japanese spider crabs live in deep waters off the coast of Japan, at depths of up to 2,000 feet (610 meters). There are several reasons why they live in deep waters.

First, the deep waters are colder, and Japanese spider crabs prefer colder temperatures. Second, the deep waters are richer in food, and Japanese spider crabs have a large appetite.

Third, the deep waters are safer from predators. Japanese spider crabs are slow-moving and vulnerable to predators in shallow waters.

However, Japanese spider crabs must migrate to shallow waters to mate. The water in shallow waters is warmer, and this helps to stimulate the crabs’ reproductive cycle.

14. Its Japanese Name Translates To “Long-Legged Crab”

The Japanese spider crab (Macrocheira kaempferi) is a fascinating creature, and its Japanese name, taka-ashi-gani (高足蟹), literally translates to “long-legged crab”.

This name is perfectly fitting, as the Japanese spider crab has the longest leg span of any arthropod in the world.

15. The Japanese Spider Crab Has The Longest Life Span Among Crabs

Teddy Yoshida, Public domain, via Wikimedia Commons

The Japanese spider crab is one of the longest-lived crabs, with a lifespan of up to 100 years. The reason why the Japanese spider crab has such a long lifespan is not fully understood.

However, some scientists believe that it may be due to its slow growth rate and its deep-sea habitat.

The Japanese spider crab takes many years to reach adulthood. It typically takes around 20 years for a Japanese spider crab to reach its full size. However, some crabs have been known to take up to 40 years to reach full maturity.

The oldest known Japanese spider crab was 127 years old. It was a female crab that was captured off the coast of Japan in 2016.

The above facts leave us with a profound appreciation for the wonders that inhabit the depths of our oceans. This colossal crustacean, with its astonishing size and unique adaptations, serves as a testament to the remarkable biodiversity that thrives beneath the waves.

While not endangered (yet!), the Japanese spider crab is also threatened by overfishing and habitat loss. It is important to take steps to protect this amazing creature, such as reducing our consumption of seafood and supporting conservation efforts.