The Japanese Spider Crab

What is the Japanese Spider Crab?

The world largest arthropod is the Japanese Spider Crab. They are called spider crab because their long thin legs make them look like spiders! You can see a picture of one here.

Japanese Spider Crab in the Singapore Underwater World in Sentosa Island
The Japanese Spider Crab is the World’s Largest Crustacean and Arthropod. This photo was taken at the Singapore Underwater World in Sentosa Island

The Japanese Spider Crab can weigh up to 20kg (44 lb) and, when fully stretched out, can measure 4 metres (13 feet) from the tip of one leg to the other! Their body is small compared with their legs, but can still reach 60cm (2 feet). They have 10 legs – the front two legs are used as claws for feeding. Although it is the world’s biggest Crustacean, it is not the world’s heaviest – the American Lobster weighs more.

Where does the Japanese Spider Crab Live?

The Japanese Spider Crab is found in the Pacific Ocean around Japan. They spend most of their time living under water – they can live in water as deep as 200-300m (220-330 yards). They can live up to 100 years old. They have orange body with white spots on their thin legs. Their eyes are situated on the front, and two thorns stick out between them. During the spring time they lay eggs in waters as shallow as 50 m (165 feet). They eat plants, algae, and small fish. Their long legs help them to move quickly to catch their prey.

What is a Spider Crab?

There are about 700 types of Spider Crab in the world – they have shells with a point at the front, and often have long legs. These are about 10% of the know species of Crab – scientists call them Brachyura, which means “short tail”. Crabs are crustaceans with only a short tail or none at all. The crabs are grouped together with lobsters and shrimp into a group called Decapods (ten feet), and then again into a larger group of crustaceans with about 22000 species. Surprisingly, this larger groups name (Malacostrata) actually means “soft shell”! Malacostrata are Crustaceans, and the Crustaceans are grouped together with spiders, insects, millipedes and scorpions into a phylum called the Arthropods.

So, the Japanese Spider Crab, as well as being the world’s largest Arthropod, is also

  • The world’s largest Crustacean,
  • The world’s largest Malacostrata,
  • The world’s largest Decapod,
  • The world’s largest and heaviest Crab, and
  • The world’s largest and heaviest Spider Crab

It’s not the heaviest Arthropod, Crustacean or Decapod – that honor goes to the stocky American Lobster, which outweighs the Japanese Spider Crab by 2kg (4.5 lb).

Japanese Spider Crabs and Humans.

People eat Japanese Spider Crabs. They are considered a delicacy in various parts of Japan, where it is salted and steamed. Unfortunately, in some parts, people have caught too many, and the numbers of Japanese Spider Crabs is dropping. Now, there are some efforts to protect the Japanese Spider Crab so it doesn’t die out completely – for example, fishermen are not allowed to catch them during the spring, when they lay their eggs. Japanese Spider Crabs are very gentle, and are popular in large aquaria.