As regular readers of this blog probably know, I’m pretty terrified of spiders. Oddly enough, though, I have no problems at all with another group of eight-legged creatures. Crabs have never frightened me the same way spiders do, and there are three reasons I can think of why this is.
This first is that crabs don’t spin webs, so there’s no chance you’ll walk into a gross sticky web. The second is that unless your house is on the seashore, there’s a pretty slim chance you’ll stumble across across a crab in your house — you can basically choose whether or not you want to see crabs, by simply avoiding the beach. No such luck with spiders. And thirdly, the way crabs and spiders move is very different. Moving siders are enough to make me run screaming in the opposite direction, but I’ll likely follow a moving crab and probably try and pick it up.
Even if I was afraid of crabs, I probably wouldn’t be too scared of today’s animal, the arrow crab, because it really doesn’t look much like a crab at all. Arrow crabs are found in coral reefs in the Atlantic Ocean, at depths of 10 to 30 m. They are known to occur in the west from North Carolina to Brazil, and in the east around Cape Verde.
Arrow crabs don’t grow very large, reaching lengths of only 3 to 6 cm. This only includes the crabs’ bodies, however, and not their legs, which are extremely long and thin, and can get to be 10 cm long. The most distinctive feature of arrow crabs is their long, pointed head, that has cool serrated edges. These crabs can be a lot of different colours, from golden to cream to yellow or brown, with black or iridescent stripes. Their claws are a beautiful bright blue.
Arrow crabs are active mostly at night, hiding under rocks and sea fans. They come out after dark to feed, and are quite territorial, especially with members of their own species. Arrow crabs scavenge whatever they can find, but will also hunt feather duster worms and other small coral animals.
Reproduction in arrow crabs isn’t particularly exciting. Male crabs grab females and deposit spermatophores onto their abdomens, which the females can use to fertilize their eggs. The females carry their eggs on their abdomens until they hatch, at which point the larval crabs are on their own. The young crabs swim to the ocean surface, where they feed on plankton until they moult into their adult forms.
Arrow crabs are quite common in aquaria, and are used to control bristle worm populations. They are pretty neat looking, so I can definitely see the appeal of having one. Still, I’ve never had much of a desire to have an aquarium, so I don’t think I’ll be getting an arrow crab anytime soon.
Cover image by NOAA / Greg McFall-, Public domain, via Wikimedia Commons
Our Wild World 
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