The Japanese spider crab is a large catch for any fisherman. With a leg span of 13 feet (4 meters) and an average weight of around 40 pounds (16-20 kg), it claims the title of largest crab. It may also have the longest lifespan of any crab, living to be 100 years old. However, Japanese spider crabs do not survive very long without injury. Their long legs are weak, and a study found that three-quarters of surveyed crabs were missing at least one limb. To protect themselves from predation, the smaller and younger crabs can decorate their shells with objects such as kelp.