What is a Spider Crab?

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.

A spider crab is a type of marine crustacean known for its long, spindly legs and a body shape that resembles a spider. They belong to the family Majidae and are found in various oceanic environments. The Japanese spider crab, for instance, holds the record for the largest leg span of any arthropod, reaching up to 12 feet from claw to claw.

Spider crabs inhabit different ocean floors around the world, from shallow coastal waters to deep sea vents. They are particularly common in the waters off Japan, where the giant Japanese spider crab resides. These creatures are adaptable and can be found at depths of up to 2,500 feet, showcasing their remarkable versatility in various marine ecosystems.

Spider crabs are omnivores and scavengers, feeding on a variety of organic materials. Their diet includes plants, algae, smaller crustaceans, dead animals, and detritus. They use their long pincers to forage and pick up food, playing a crucial role in the ocean's ecosystem by helping to clean up the sea floor.

Spider crabs reproduce through a process called external fertilization, where the female releases eggs into the water, and the male fertilizes them. The female then carries the fertilized eggs on her abdomen until they hatch. This reproductive strategy is common among marine arthropods and ensures the wide dispersal of their offspring in the ocean currents.

The conservation status of spider crabs varies by species. While many spider crab species are not currently endangered, some, like the giant Japanese spider crab, face threats from overfishing and habitat destruction. Efforts are being made to ensure sustainable fishing practices and protect their natural habitats to prevent their numbers from declining.

While smaller species of spider crabs can be kept in home aquariums, they require specific conditions such as the right salinity, temperature, and tank size to thrive. Larger species, like the giant Japanese spider crab, are not suitable for home aquariums due to their massive size and complex needs. Public aquariums with specialized facilities are better equipped to house such large species.