Despite my unreasonable fear of spiders, I’ve never had much of a problem with crabs, even though they also have eight legs. Maybe it’s because crabs don’t move in the same creepy way that spiders do. Or maybes it’s the fact that crabs can’t make webs. Whatever the reason, I usually don’t find crabs particularly frightening. There is one crab I would never want to meet in the ocean though: the Japanese spider crab.

These crabs are found of the coast of Japan, on the east side of the islands of Honshu and Kyushu. They live on the sea floor, at depths of 150-300 meters, though they can be found as deep as 600 meters. Younger crabs tend to be found in shallower waters, up to 50 meters. Japanese spider crabs are generally found around holes and vents in the deep parts of their range.

A picture showing the long, long legs of a Japanese spider crab. The carapace (shell) of the crab stops growing fairly early in its life, but the legs keep growing.  Source: Wikipedia
A picture showing the long, long legs of a Japanese spider crab. The carapace (shell) of the crab stops growing fairly early in its life, but the legs keep growing. Image by Lycaon (Hans Hillewaert), CC BY-SA 3.0, via Wikimedia Commons

Alright, now to the point of this post: the reason I feel slightly uneasy when looking at pictures of Japanese spider crabs. Firstly, as their name suggests, spider crabs look a lot more like spiders than normal crabs. More importantly, Japanese spider crabs are the biggest species of arthropod in the world. They have a legspan of up to four meters, though they only weigh 19 kilograms. Basically they’re all legs.  The shell is orange and spotted, and does not change colour or attempt to camouflage the crab.

To breed, spider crabs move to shallower water in the spring, usually between January and March. The male produces a spermatophore, and then inserts it into the female using his claws. That doesn’t sound very pleasant to me, but maybe it feels good o the crabs, who knows? The female lays up to 1.5 million eggs, of which only a few survive. The mother carries the eggs on her back until hatching, so she can protect them and keep them well oxygenated with her legs.

Okay this picture creeps me out a bit – just all the spider like things in it make me shiver. These crabs are often kept in aquaria because of their gentle natures. Image by Laika ac from USA, CC BY-SA 2.0, via Wikimedia Commons

My fears about meeting a 4 meter long crab that is vicious and will attack me are nonsense – Japanese spider crabs are very docile. They spend their days wandering the sea floor in search of food, and cannot swim. They are scavengers, eating any decaying matter they can find, whether it is plant or animal. Adults have few predators, because of their massive size. It is said that these crabs can live to be over 100 years old, although these reports are unconfirmed.

Japanese spider crabs are considered a delicacy in many parts of Japan, and so have been caught in fairly large numbers in the past. Lately the catch of spider crabs has been much less, mostly because they are becoming harder and harder to find. Fishermen are not allowed to catch the crabs during the breeding season, in an attempt to allow the species to recuperate. Unfortunately, these crabs live so deep that we don’t really have a lot of information about them, so we don’t know how vulnerable their population really is. Still, it’s better to air on the side of caution, so I’m glad we’re protecting them now!

Cover image by ReimannLukas, CC0, via Wikimedia Commons