Scarlet Reef Hermit Crab (Paguristes cadenati)

The Scarlet Reef Hermit Crab is one of the most popular and genuinely effective cleanup crew animals available in the reef hobby, and a perennial favourite for good reason. Named for its bright red legs contrasted against a vivid yellow face, this striking little crab is native to the reef faces and coral rubble of the Caribbean and Western Atlantic, where it scavenges animal matter and algae in large numbers. Also known as the Red Reef Hermit and Red Legged Hermit Crab, P. cadenati brings both visual appeal and meaningful cleaning performance to reef and FOWLR systems of all sizes. Despite a voracious appetite and constant feeding activity, the Scarlet Reef Hermit only grows to approximately 1.5 inches in length, keeping it manageable and suitable for a wide range of tank sizes. Hardy, peaceful, and endlessly active, this is a cleanup crew staple that earns its place in almost any marine system.

Why we love them

• Particularly effective against filamentous algae, hair algae, slime algae, and cyanobacteria, tackling some of the most persistent and frustrating nuisance growth a reef keeper faces
• Bold red and yellow colouration makes it one of the most visually attractive small hermit crabs available; easily spotted working the rockwork and substrate
• Hardy and requiring minimal care in a well-established system, making it suitable for beginner and experienced hobbyists alike
• More peaceful toward tankmates than many other hermit crab species, making it a safer choice in systems with a diverse cleanup crew
• Can be kept in groups and works effectively alongside other cleanup crew species to cover different zones and algae types

Suggested parameters

• Temperature: 24 to 26°C (75 to 79°F)
• Salinity: 1.025 to 1.026 SG
• pH: 8.1 to 8.4
• Alkalinity: 8 to 10 dKH
• Calcium: 400 to 450 ppm
• Magnesium: 1250 to 1400 ppm
• Nitrate: 5 to 20 ppm
• Phosphate: 0.03 to 0.12 ppm
• Copper-based medications are immediately fatal to all invertebrates and must never be used

Care and temperament

• Difficulty: Easy
• Temperament: Peaceful toward fish and corals; like all hermit crabs, capable of targeting snails for their shells, particularly when suitable empty shells are not available
• Reef safe: Yes, fully compatible with corals and most ornamental invertebrates
• Minimum tank size: 40 litres (10 gallons); suitable for nano systems and larger displays alike
• Best kept in an established reef system with ample live rock and a healthy supply of natural algae growth; a new or sterile system may not provide enough food to sustain them
• A selection of empty shells in graduated sizes must always be available; keeping plenty of appropriately sized empty shells reduces but does not entirely eliminate the tendency to target snails

Feeding

Scarlet Reef Hermit Crabs are self-sufficient scavengers in most established reef systems.

• Will eat almost anything in the aquarium including fish food and invertebrate diets, but algae and detritus form the core of their natural diet
• When algae levels drop significantly, supplement with dried seaweed, nori, or other marine foods to prevent starvation and reduce the likelihood of them targeting other invertebrates
• Quality sinking pellets placed near the rockwork are also accepted
• No target feeding is necessary in a well-established system with healthy algae growth

Stocking and compatibility

• Stock conservatively relative to actual algae load; overstocking leads to food competition and increased aggression over shells
• Excellent alongside Blue Leg Hermit Crabs, Trochus snails, Cerith snails, and other peaceful reef cleanup crew members; each species covers slightly different zones and algae types
• Avoid large predatory fish such as triggerfish, pufferfish, and large aggressive wrasses that will target small crustaceans
• Reef safe with corals but may attack snails and other hermit crabs for their shells; providing a generous supply of empty shells in the right size range is the most effective way to manage this behaviour
• Do not house with large aggressive crab species that may prey on or outcompete them

Health and acclimation notes

The Scarlet Reef Hermit Crab is sensitive to rapid changes in salinity and water chemistry during acclimation. Drip acclimation is recommended for all invertebrates before introduction to the display. Maintaining a supply of appropriately sized empty shells at all times is the most important ongoing care requirement; a hermit crab without a suitable shell to move into during molting is stressed and vulnerable. Regular water changes replenish the mineral levels that support healthy exoskeleton and shell growth. Copper-based medications must never be used in any system housing this or any other invertebrate.

What you are buying

• You will receive: 1x Scarlet Reef Hermit Crab (Paguristes cadenati)
• Legs and chelae are bright red; antennae are deep red; eyestalks are vivid yellow to yellowish-orange; shell colouration varies depending on the shell currently occupied and often carries encrusting coralline algae
• Quantity per order as listed; adult size is approximately 3 to 4 cm including shell

Drip acclimation is recommended. Empty shells in graduated sizes must be maintained in the system. Copper-based medications must never be used in any system housing this animal.