Arrow Crab

Unique Spider-Like Reef Scavenger

The Arrow Crab (Stenorhynchus seticornis), also known as the Spider Crab, is a distinctive and beneficial reef invertebrate recognized by its elongated legs, pointed rostrum (nose), and triangular body shape. These fascinating crabs are valued for their scavenging abilities and their effectiveness at controlling bristleworm populations in reef aquariums.

Why Arrow Crabs Are Valuable

• Natural pest control: Actively hunts and consumes bristleworms, making them excellent for managing unwanted worm populations
• Efficient scavenger: Feeds on detritus, uneaten food, and decaying organic matter to help maintain water quality
• Striking appearance: Features long, spindly legs with distinctive banding and a cream to tan body with reddish-brown markings
• Active and entertaining: Constantly on the move, exploring rockwork and hunting for food
• Nocturnal behavior: Most active during evening hours and at night

Care Requirements

Temperature: 72–78°F
Salinity: 1.023–1.025 specific gravity
pH: 8.1–8.4
Tank Size: Minimum 30 gallons recommended
Rockwork: Requires plenty of live rock with caves and crevices for shelter

Arrow crabs are opportunistic feeders that will scavenge throughout the aquarium. In well-fed reef systems, they typically receive adequate nutrition from leftover food and natural prey. Supplemental feeding with meaty foods like mysis shrimp, chopped seafood, or sinking pellets can be offered 2-3 times per week.

Important Considerations

While generally reef-safe, arrow crabs can be territorial with their own species and should typically be kept individually unless housed in very large aquariums. They may occasionally nip at slow-moving fish or small ornamental shrimp if hungry. Arrow crabs are excellent additions to fish-only or mixed reef systems where bristleworm control is desired. They will molt periodically as they grow and should not be disturbed during this vulnerable time.

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