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Invertebrates

beginner

Arrow crab care

Stenorhynchus seticornis · Inachidae (spider crab)

Also called: yellowline arrow crab, arrowhead crab, Stenorhynchus

Checked against 3 sources on · reefcalcs editorial

Quick reference

Care level

Beginner

Adult size

About 6 in, some up to 10 in (LiveAquaria); females smaller[1, 2]

Lifespan

No reliable source found

Reef safe

With caution: may pick at polyps and eat small fish or shrimp when hungry[2, 1]

Diet

Carnivorous opportunist: meaty, flake and tablet foods[1, 2]

Tank size

Neither LiveAquaria nor Quality Marine gives a minimum; both describe a 6 in crab that wants established rockwork with caves and crevices.[1, 2]

Temperature

72–78 °F (Quality Marine)[2]

Salinity

35 ppt (SG 1.0264 at 25 °C)

pH

8.0–8.4

What is an arrow crab?

Stenorhynchus seticornis is the Caribbean arrow crab, which LiveAquaria calls the most common arrow crab in the trade.[1] Quality Marine says it's mostly nocturnal, hiding in caves and rubble by day.[2] Its appeal to reefers is that it eats smaller bristleworms.[1]

Feeding

LiveAquaria says it accepts almost all meaty, flake and tablet foods.[1] Quality Marine's warning is the important one: without enough food it may pick at mushrooms, polyps or small fish.[2] Feed it a little meaty food every day or two rather than leaving it to forage.

Aggression and spacing

LiveAquaria rates it semi-aggressive and says it has been known to attack crustaceans such as banded coral shrimp, and even small, slow-moving fish.[1] A Reefs.com writer describes arrow crabs as long-lived and often peaceful, but notes many reports of them being very poor additions to a home tank.[3]

Tankmates

LiveAquaria lists it as reef compatible; Quality Marine advises caution because hungry crabs pick at soft corals and polyps.[1, 2] Avoid small shrimp and small, slow-moving fish.[1] Quality Marine says invertebrates don't tolerate copper medications.[2]

Disease and quarantine

Quality Marine recommends adding it to a well-established aquarium with plenty of rockwork, cracks and caves.[2] It doesn't tolerate copper medications.[2]

Troubleshooting

Small shrimp or a goby vanished

Likely cause: Arrow crab predation, mostly at night.[1]

Fix: Rehome the crab or the small tankmates.[1]

Polyps closed or mushrooms damaged

Likely cause: A hungry crab picking at them.[2]

Fix: Feed it more often.[2]

Bristleworms still everywhere

Likely cause: It eats small worms, not large ones.[1]

Fix: Trap the big ones.

Common mistakes

  • •Adding it to a tank with small shrimp.[1]
  • •Relying on it to find all its own food.[2]
  • •Expecting it to clear large bristleworms.[1]

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Equipment & food for this species

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Inverts need stable salinity — use a refractometer, not a hydrometer.

PE Mysis Shrimp — frozen

Frozen mysis shrimp.

See options on Amazon
Refractometer for saltwater + calibration fluid

Calibrate with 35 ppt fluid monthly. Replaces hydrometers.

See options on Amazon

Arrow crab FAQ

Do arrow crabs eat bristleworms?
Smaller ones, yes: LiveAquaria says they may eat smaller bristleworms.[1]
Are arrow crabs reef safe?
Mostly. LiveAquaria lists it as reef compatible, but Quality Marine says a hungry crab may pick at mushrooms and polyps.[1, 2]
Will an arrow crab eat fish?
It may attack small, slow fish, and it has attacked banded coral shrimp.[1, 2]
How big do arrow crabs get?
About 6 in across, some to 10 in, with females smaller.[1, 2]

Sources

  1. LiveAquaria — Arrow crab (retailer care sheet)
  2. Quality Marine — Arrow crab (wholesaler care sheet)
  3. Reefs.com — on arrow crabs in home aquaria

Spotted something out of date? The corrections log lists every change we make.

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