Japanese Spider Crab



The Japanese spider crab is a HUGE arthropod living in the Pacific Ocean. Although they look quite different than what most people expect when they think of a crab, this weird invertebrate is still considered a crab. After all, what else would you call it? Okay, maybe a spider, but that’s why it has spider in its name! These animals, as you will find out later, are very large, but they pose almost no threat to humans. This is because the move extremely slowly. Their legs are so long that they are also quite weak. Therefore it is hard to move them. Their legs are so week in fact that approximately three-fourths of these animals are missing one or more legs! The legs fall off easily when a net or predator catches on to them. They sometimes grow back when individuals molt. Both males and females are mostly orange with white places.


Like I said earlier, these crabs are very large. They are, in fact, the largest arthropods on the planet. A full grown individual can have a body measuring 15 inches (37 cm) across. Their leg-span is much larger. A full grown individual can be up to 13 feet (4 m) across including its legs! These crabs are not the heaviest arthropods on the planet, but they come very close. The American lobster is the heaviest, but Japanese spider crabs can weigh up to 44 pounds (20 kg). If you read the American lobster article, you will find that their maximum weight is the same as the spider crab’s, but for some reason the lobsters are called heavier. This may be because their average weight is higher.


Japanese spider crabs are ocean scavengers. The do not hunt for their food, but instead find dead and decaying plant and animal matter along the sea floor. Animals like these help make the ocean a cleaner place not cluttered with dead organic matter. Sometimes they will eat living algae or kelp, but almost never living animals. This is because they are extremely slow. Any living animals they eat are marine invertebrates that are too slow to easily escape. Sailors of the past would tell stories of these animals dragging sailors under the water and eating them. This is mostly untrue, and these legends may have come from people seeing spider crabs eating previously drowned sailors.

Habitat and range

Although these invertebrates could easily call much of the coast in the world home, they are restricted mainly to the area east of Japan. There was one instance in which an individual was found much farther south than its normal range, but it is assumed that it was carried there in severe weather or after being caught in a large fishing net. As I said earlier, spider crabs live on the ocean floor. They normally inhabit depths of 500-1,000 feet (150-300 m) but can be found up to 2,000 feet (600 m) deep. When mating they are in shallower water, 165 feet (50 m) below the surface. Younger individuals typically stay in warmer and shallower waters than the adults.


Like all invertebrate, Japanese spider crabs must molt as they grow. During these times are when they are most vulnerable to predators, as their next exoskeleton has not yet formed completely. They also grow back lost legs at these points in their life.

Status and threats

Most full grown adults are way too large to be eaten by any ocean predator. Juveniles are vulnerable to predators, but they have a technique to survive. They will put sponges, kelp, and other ocean life on their shell to disguise themselves. One of this animal’s predators is the manta ray, which primarily eats them right after the spider crabs molt. These animals have not been evaluated by IUCN or CITES. Although they are not thought to be extremely endangered, there are a few minor plans that have been implemented to help these animals survive. These include laws against fishing for them and restocking the wild with juveniles.

Reproduction and young

Much of the normal information regarding these animals’ reproduction is lacking. Spider crabs mate during the late winter and early spring, from January to March. Females lay up to 1.5 million tiny eggs each year. The eggs are carried on the female’s back and hatch after 10 days. After this, the parents have no interaction with their young. The young are legless and transparent when they first hatch, and it takes a long time for these creatures to reach their full size. They can live up to 100 years in the wild.

Don’t forget to scroll down and comment your guess about what the next animal is!


(Sorry for the bad view, this was the best image I could use.)


Photo credits:

  • Japanese Spider Crab – Tsarli
  • Mystery animal – public domain

One Response

  1. Charis Dwire
    Charis Dwire at |

    Looks like a marlin to me.

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