Weirdo alert! If you’re looking for an unusual crustacean addition to your marine aquarium, you’ve found it. Let us introduce you to this spindly number: the arrow crab. With its extremely long spindly legs and unicorn-like horn on its head, this crab is hard to overlook.
Keep reading for everything you need to know about keeping arrow crabs in your aquarium!
|Name (Common, Scientific)||Arrow crab, arrowhead crab, yellowline arrow crab, spider crab, Stenorhynchus seticornis|
|Minimum tank size||30 gallons|
|Minimum group size||1|
Arrow crab description & natural habitat
As mentioned in the introduction, the arrow crab will make any visitor look twice at your aquarium. Also known as spider crab, this species is easily recognized from its very long legs and strange head protrusion.
There are various species in the Stenorhynchus genus (see the last paragraph for more info), but when we refer to the ‘arrow crab’ it’s usually Stenorhynchus seticornis. This particular variety is also referred to as the yellowline arrow crab, a common name derived from the fact that it has thin yellow lines running over the top of its rusty-colored extremities.
The arrow crab can grow relatively large, with a leg span of around 8”; that’s about the size of an adult person’s hand. Females do stay smaller than the males.
This crab species is naturally found in the western Atlantic Ocean. Here, it inhabits shallow coral reef environments, mostly hiding in and around Lebrunia anemones during the day and coming out at night to feed on feather duster worms and other small reef critters.
We spotted wild arrow crabs in the Caribbean Sea around the island of Curaçao, where they’re common; see the cover photo at the top of this post. Despite the fact that they’re nocturnal and don’t really like light, it’s easy enough to spot them if you peek inside crevices and under rocks with a flashlight.
Arrow crab aquarium
If you’d like to keep an arrow crab in your aquarium, keep in mind that they can cause trouble in smaller tanks. Something of 30 gallons or up is preferable.
Because crabs like this one prefer to spend at least a big chunk of the day in hiding, make sure there’s plenty of cover available in the aquarium. Think rocks, corals and anything that creates crevices and offers some shade.
Arrow crab compatibility
The arrow crab is easy to care for, but we’ve listed it as intermediate difficulty mostly because of compatibility issues that might arise with this species. Crabs are opportunistic omnivores and many species can cause issues when they get hungry.
The arrowhead crab is only tentatively reef safe as hungry specimens don’t have qualms about munching on coral polyps. They might even snatch small live fish if they get the chance!
Any fish species you introduce into an aquarium that also houses an arrow crab should be large and quick enough to avoid those snippy pincers. Small, friendly fellow crustaceans like shrimp are at an especial risk.
Feeding Arrow crab
The advantage of the arrow crab’s ravenous omnivorous nature is that feeding it is an absolute breeze. They’ll feed on any bits they can find in the tank, whether alive or dead. Bristle worms make a welcome snack, which is why the species is often introduced into a tank to combat plagues of them.
To supplement your arrow crab’s diet, offer sinking foods like invertebrate tablets that the other aquarium inhabitants might not get to as quickly. Other than that, these crabs will just eat whatever leftovers make their way to the bottom of the tank.
Decorator arrow crab (Stenorhynchus sp.)
Another well-known crab that is often kept in the aquarium is the decorator arrow crab. These are members of the same genus as the arrow crab (Stenorhynchus) and are also commonly referred to as spider crab. However, the normal arrow crab (Stenorhynchus seticornis, which we’ve discussed here) doesn’t use pieces of its environment as ‘decorations’.
Don’t confuse the decorator arrow crab with other decorator crabs either. There are quite a few crabs out there that will snag different pieces of aquarium décor, and not all of them are members of the genus Stenorhynchus. You’ll recognize the decorator arrow crab specifically from its spindly extremities. It has a more bland greyish color than the normal arrow crab and more ‘hairy’-looking frills protruding from its body.
Not all decorator arrow crabs look the same, as there are a few varieties out there. Their care and temperament is the same as that of the normal arrow crab.
A marine aquarium inhabited by funky crustaceans like the arrow crab is an endlessly entertaining addition to your home but requires specialized knowledge to thrive.
If you prefer leaving things to the experts, FantaSEA Aquariums can help! We design, build and maintain aquariums of all shapes and sizes for our clients. Contact us here with your ideas.
PS: Love the arrow crab? Have a look at the list of our favorite aquarium crabs to meet more of the funky invertebrates our oceans have to offer.