King crabs are the giants of the cold northern seas. The red king crab, the best known of about 120 species, can reach a leg span of 5 feet (1.5 m) and a weight of 24 lbs (11 kg). Its shell is covered in sharp spines and is dark red to burgundy in life.
Look closely and a king crab seems to have only six walking legs plus its claws. The fifth pair is tiny and tucked under the shell, a clue that king crabs are not true crabs but descend from hermit crab ancestors. The right claw is bigger than the left and is used for crushing.
King crabs grow by molting and can live 20-30 years.
Red king crabs live in the cold waters of the Bering Sea, the Gulf of Alaska, the Sea of Okhotsk and around the Kamchatka Peninsula and northern Japan. Other king crab species live in cold or deep water around the world, including the Antarctic.
Adults are found on sand and mud from about 30 feet (10 m) down to more than 650 feet (200 m). Red king crabs introduced to the Barents Sea by Soviet scientists in the 1960s have since spread along the coast of Norway, where they are now an invasive species.
King crabs eat worms, clams, mussels, barnacles, brittle stars, sea urchins and other small animals they find on the seabed, as well as dead fish. Young crabs feed on tiny organisms living on the bottom.
Young red king crabs gather by the thousands in tightly packed heaps called pods, which protect them from predators. Adults make long seasonal migrations, moving into shallow water in late winter to molt and mate and back to deep water for the rest of the year.
A female carries up to 400,000 eggs under her tail for nearly a year before they hatch.
King crabs make up the family Lithodidae. Along with the red king crab, the blue and golden king crabs of Alaska are important commercial species. None has been assessed by the IUCN, but the fisheries are closely managed with quotas and seasons, and the dangerous winter crab fishery in the Bering Sea became famous through the television series Deadliest Catch.
Warming seas and shifting food supplies are a concern: Alaska closed its Bering Sea red king crab fishery in 2022 after surveys found far fewer crabs than expected.
