Beneath the depths of the ocean lies a realm inhabited by one of the most extraordinary creatures known to science – the Japanese Spider Crab (Macrocheira kaempferi). As enigmatic as it is colossal, this species of marine crab captivates researchers and enthusiasts alike with its massive size and unparalleled appearance.

Inhabiting the waters around Japan, the Japanese Spider Crab stands as one of the largest arthropods in the world, boasting a unique body structure and a remarkable set of elongated legs that have earned it the moniker “Spider Crab.”

Join us on a captivating journey as we delve into the captivating world of the Japanese Spider Crab, a true wonder of the deep seas.


The crab’s body is spherical and elongated, with a reddish-brown exoskeleton that protects its internal organs. The carapace, or shell, is broader in front and narrows towards the back. It has a maximum width of 40 centimeters (15.7 inches).

The Japanese Spider Crab’s long and thin ten legs are their most distinctive characteristic. It has eight spine-covered legs that are segmented. The front two pairs of legs are greatly enlarged and resemble the legs of a spider, therefore the name “Spider Crab.” These legs may stretch about 3 to 4 meters (9.8 to 13.1 ft), making them the longest crab species.

The legs of the Japanese spider crab can grow up to 3-4 meters in length
The legs of the Japanese spider crab can grow up to 3-4 meters in length

The Japanese spider crab, like other crabs, has two pincers, or chelipeds, at the front of its body. The “crusher claw” of the enormous claw is utilized for crushing and breaking apart prey. The little claws are more versatile and are used for item control and manipulation. An adult male’s chelipeds are much longer than his walking legs, whereas a female’s chelipeds are significantly short.

The spines and sharp hooks on the legs are abundant. These characteristics help them grasp the surface and traverse their surroundings. The spines also act as a defensive mechanism, deterring possible predators.

The exoskeleton of the Japanese spider crab tends to be reddish-brown, but the color and intensity may vary. The crab’s hue helps it blend in with its rocky and sandy surroundings, giving camouflage and safety.


Japanese Spider Crabs act as scavengers, preying on dead and decaying organic matter. They execute a vital role in the environment by cleaning the ocean floor and devouring carrion. They have a highly developed sense of smell, which allows them to recognize and locate prospective food sources.

Japanese Spider Crabs are scavengers, preying on dead and decaying organic matter
Japanese Spider Crabs are scavengers, preying on dead and decaying organic matter

Their scavenging nature means these crabs are opportunistic feeders, meaning they will eat a range of species it comes across. Small fish, mollusks, crabs, sea urchins, and sea stars may be part of their diet. They have also been observed feeding on the carcasses of other marine species, such as whales.

Plant material augments the diet of Japanese Spider Crabs. They eat a variety of algae, such as kelp and seaweed, which they scrape off rocks and other surfaces using their specialized mouthparts.

Japanese Spider Crabs are not active predators due to their mobility. Instead, they smash and break down their meal with their strong pincers. Their front claws have been uniquely designed for this purpose, the more giant claw serving as a crusher for shattering shells and hard the exoskeleton, and the smaller claw assisting in manipulating and managing their meal.

Their feeding habits may differ based on environment and food availability. They are reported to be more active at night when they travel in search of food. Their scavenging activity enables them to consume diverse food items, ensuring survival in the deep-sea ecology.


The Japanese spider crab is only found in Japan’s surrounding territories. They are mainly widespread in the country’s southern and southwestern areas. They live in deep-sea habitats. They are usually found in depths of 50 to 600 meters (164 to 1969 ft). These crabs are benthic, which means they live on or near the ocean floor. They favor rocky and sandy bottoms where they may seek refuge and hide.

The Japanese spider crab carapace stay the same size when they become adults but the legs keep growing
The Japanese spider crab carapace stays the same size when they become adults, but the legs keep growing


The Japanese Spider Crab’s mating season usually lasts from January to April. Male crabs aggressively seek receptive female companions during this period. To attract females, male crabs engage in a variety of courting rituals. To communicate and exhibit their intentions, they use delicate stroking, caressing, and subtle clicking sounds with their claws.

When a man finds a compatible female, he transfers sperm to the “spermatophore,” a specialized organ on his abdomen. The male grabs the female and inserts the spermatophore into her reproductive entrance to ensure her eggs are fertilized. Internal fertilization happens within the female reproductive system. As the eggs move through the oviducts, sperm fertilizes them.

Fertile eggs are carried by the female on her abdominal flap, also called “abdominal pleopods,” until they hatch. Depending on the size and age of the female, the number of eggs produced might range from several thousand to over a million. The phase of brooding lasts months. The Japanese Spider Crab larvae emerge after the eggs hatch. They are called zoea larvae and live in the plankton. They are small at this stage and go through multiple molting phases as they grow and mature.

The zoea larvae metamorphose after drifting in the ocean currents for an extended period. They evolve into megalopae, which are bigger and seem more crab-like. The megalopae eventually settle on the ocean floor and undergo further molting stages to develop into juvenile crabs. Over the years, they mature into adult Japanese Spider Crabs.

Despite their enormous size, spider crab larvae are small and float around like plankton
Despite their enormous size, spider crab larvae are small and float around like plankton


The crab faces several threats to its population. Some of them include

  • Overfishing
  • Habitat destruction due to human activities
  • Pollution
  • Rising water temperatures

Facts About The Japanese Spider Crab

  1. The Japanese Spider Crabs are also known as “Taka-ashi-gani” in Japanese, which translates to “tall legs crab.”
  2. Their long legs allow them to move gracefully across the ocean floor.
  3. Their legs can regenerate.
  4. The largest recorded specimen had a leg span of about 5.5 meters(18 feet).
  5. They have remarkable lifespans and can live up to 100 years.
  6. This species is a member of the “decorator crabs” group, which has been recorded embellishing its shells with sponges, plants, and anemones.


How big can Japanese Spide Crabs grow?

Japanese Spider Crabs are known for their impressive size. Their legs can grow 3 to 4 meters (9.8 to 13.1 feet).

Are Japanese Spider Crabs dangerous to humans?

Despite their frightening look, Japanese Spider Crabs are typically regarded as gentle and pose little harm to people. To minimize unintentional injury, it is best to use caution and avoid touching them.

Can Japanese Spider Crabs regenerate their lost limbs?

Like many other crabs, Japanese Spider crabs can regenerate lost limbs.

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