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What is a Spider Crab?

A spider crab is a marine crustacean known for its long, spindly legs and camouflage abilities. These intriguing creatures inhabit various ocean depths, often decorating themselves with sponges and algae for protection. Their unique adaptations make them a fascinating study in marine biology. Curious about how they thrive in their underwater realm? Dive deeper with us into the world of spider crabs.
Christine Hudson
Christine Hudson

A spider crab is a member of the crustacean family Madijae, which includes around 700 crab species. The common characteristics of these crabs are a body which is slightly longer than it is wide and legs which are very long. These characteristics are what have given the crab its common name of “spider crab."

The largest species of spider crab is the Macroheira kaempferi, or Japanese spider crab. This crab has the longest legs of any arthropod known, and these legs can span up to 12.5 feet (3.8 meters). Typically, the Japanese spider crab lives as a carnivore, scavenging meat from dead sea creatures. While it is native to the southern seas of Japan, it is not heavily fished—most of the crabs caught span only between 3 and 7 feet (about 1 and 2 meters), while the larger crabs are left alone. These crabs can live for 100 years or more.


Another widely-known species of spider crab is the Maja squinado, or European spider crab, which usually live in the mud of soft sea beds. These crabs are much smaller than their Japanese counterparts, averaging as little are .7 feet (about 22 cm), and they live only five to 10 years. The European spider crab also lives on an omnivorous diet with a wide range of food such as algae, mussels, and plankton. Also differing from the Japanese variety, these crabs are commercially fished, with at least 70% of the yearly catch being found off the coast of France.

With 700 or more species of spider crab, it may be hard to explain each species. While most have spiny exoskeletons, very long legs, and a long body, there are some which don’t look much different than other kinds of crab. All spider crab do, however, have 10 legs with the first two tipped in claws. Many use the spines and hooks on their backs to purposefully attach seaweed, dead creatures, and other debris to them for extra camouflage. These species can be found all over the world, with some even being discovered in the depths of the Antarctic.

Like many crustaceans, the spider crab does go through a molting phase as it outgrows its “shell." This occurs throughout the life of the crab. Mating season may not be the same every year, as it begins as soon as the female crab molts. Fertilization of the eggs happens internally, and then the female lays them in shallow waters with lots of weeds and rocks to protect them.

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Discussion Comments


Wow, I had no idea that crabs could live for 100 years or more. Imagine what it would be like to be an old man crab. You would have spent so much time on the earth with a tiny little brain and a very awkward body. I wonder how many actually make it this far?


Maybe I am mistaken, but I thought that the spider crab was more commonly known as the Alaskan King Crab. The name change has everything to do with marketing. Eating a kind crab sounds a lot more appetizing that eating a spider crab.

This practice is actually more common than you would expect. I know that Chilean Sea Bass used to have a much less appetizing name, something about bottom sucking if I recall. They just slap a new name on it and suddenly the exact same thing is fit for a menu spot on some of the fanciest restaurants.

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