Arrow crabs get their name from their triangular shaped main body, but they are also know as Spider Crabs, or Frilly Arrow Crabs. It’s easy to see why they would commonly be called Spider Crabs!

Decorator Arrow Crab

For those of us with arachnophobia, the Decorator Arrow Crab probably isn’t the best choice as a new addition to your aquarium. With their spindly legs and spider like movement around the aquarium, they definitely resemble something out of a horror film. (If you hadn’t guessed, spiders are my worst nightmare!)

Most Arrow crabs are considered reef safe, with caution. The reason being is that they are an opportunistic species and have been known to attack small fish and other invertebrates if they are not kept well fed. Particularly at risk would be fish like Scooter Blennies, Mandarin Dragonettes and other slower, bottom dwelling fish.

Interestingly, the Frilly Arrow Crab augments its camouflage by attaching algae and other things found in the tank to its body. The Frilly Arrow Crab likes tanks with spacious live rock openings allowing it space to hide.

They are considered a hardy species of crab, which may make them an ideal choice for a beginner looking for a centre piece. They are generally active through the day and night, and once acclimated to your tank will be a real show stopper!

Where Decorator Arrow Crabs really come into their own is cleaning up what some consider pests. Bristle Worms. They will clear a tank of Bristle Worms in no time at all.

Frilly Arrow Crab
Frilly Arrow Crab

Tank Requirements

  • These crabs are reef safe with caution
  • Clean and stable water
  • Stable magnesium & calcium levels
  • Absolutely no copper treatments within the tank
  • Iodine supplements are recommended to encourage healthy molts and growth
  • Recommended stocking level is 1 crab per tank. They will not tolerate others of their own species.
  • Lots of rockwork for it to hide it
  • No smaller fish, crustaceans or invertebrates.


  • These are carnivores.
  • They have been known to take food from corals and slower moving fish, so extra care should be taken when feeding your tank to ensure all tank mates are receiving their fair share of the goods.
  • They will eat most things you put into a tank.
  • Live foods, frozen foods, pellets and flaked food are readily accepted.


Decorator Arrow Crab
Decorator Arrow Crab

These crabs take quite a long time to acclimate. They should be drip acclimatised slowly, for roughly double the amount of time you would do for a fish, about an hour and a half.

As you are acclimating take out some of the water the crab is sitting in every 15 minutes. This will slowly increase the amount of tank water in the acclimation bucket and reduce the amount of original water.

When placing it in the tank, try to avoid netting it and exposing it to air. If you have been removing the water as you have been acclimating then the amount of original water left in your bucket should be minimal. Scoop the crab out in a container and place the container into the tank.

Crabs do not acclimate particularly well, please take your time with this process. Like most inverts, crabs are sensitive to changes in water parameters, temperature and salinity.


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