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Japanese spider crab Information and Lifecycle

Japanese Spider Crab

The Japanese spider crab (Macrocheira kaempferi) is a species of marine crab that lives in the waters around Japan. It has the largest leg-span of any arthropod. It goes through three main larval stages along with a prezoeal stage to grow to its great size.

The genus Macrocheira contains multiple species. Two fossil species of this genus have been found, M. ginzanensis and M. yabei, both from the Miocene of Japan. Its diverse taxonomic history is an important part of what these creatures are and how they evolved to be what they are today. They are sought by crab fisheries, and are considered a delicacy in Japan. Conservation efforts aim to protect these creatures and their population from overfishing. The Japanese spider crab is similar in appearance to the much smaller European spider crab (Maja squinado).


Of the 60,000 species of crustaceans on Earth, Japanese spider crabs are the largest, spanning up to 12.5 feet from the tip of one front claw to the other. They’re also one of the world’s largest arthropods, animals with no backbone, external skeletons, and multiple-jointed appendages. The Japanese spider crab has the greatest leg span of any arthropod, reaching up to 3.7 m (12.1 ft) from claw to claw.

The body may grow to 40 cm (16 in) in carapace width and the whole crab can weigh up to 19 kg (42 lb)—second in mass only to the American lobster among all living arthropod species. The males have the longer chelipeds; females have much shorter chelipeds, which are shorter than the following pair of legs. Apart from its outstanding size, the Japanese spider crab differs from other crabs in a number of ways. The first pleopods of males are unusually twisted, and the larvae appear primitive. The crab is orange with white spots along the legs. It is reported to have a gentle disposition despite its ferocious appearance.


Female crabs carry the fertilized eggs attached to their abdominal appendages until they hatch into tiny planktonic larvae. They can lay up to 1.5 million eggs per season, and these eggs hatch in 10 days on average.

Once hatched, these larvae undergo four stages of development before they mature into adulthood. The first, or prezoeal, stage lasts only a matter of minutes, with most molting within 15 minutes to enter the first zoeal stage. They look very different from their parents at this stage, with small, transparent bodies. M. kaempferi undergoes two zoeal stages and a megalopa stage before it reaches adulthood. Each of these stages is influenced greatly by temperature, both in terms of survival and stage length. The optimum rearing temperature for all larval stages is thought to be between 15 and 18 °C, with survival temperatures ranging from 11 to 20 °C. At these temperatures, the zoeal stages can last 7 to 18 days, with the megalopa stage lasting 25 to 45 days.

Spider Crab Facts

  1. It has the largest leg-span out of all arthropods
  2. Males are typically bigger and armed with larger claws
  3. Japanese spider crabs are scavengers and often do not actively hunt for prey. They prefer to scour the ocean floor for dead animals or plants.
  4. In Japan, they are considered to be a culinary delicacy.
  5. Their legs can regenerate

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