Spider Decorator Crab

Spider Decorator Crabs are fascinating ornamental crabs known for their unusual body shape, long spider-like legs, and unique decorating behavior. Also known as Camposcia Decorator Crabs, Camposcia retusa use pieces of algae, sponge, soft coral, rubble, and other available materials to camouflage their body. This natural behavior makes them one of the most interesting invertebrates to observe in a saltwater aquarium, but it also means they should be kept with caution in reef systems. Spider Decorator Crabs may pick up or attach small pieces of coral, macroalgae, sponge, or other sessile invertebrates, making them better suited for mature aquariums where their behavior can be monitored.

Introduction to Spider Decorator Crab (Camouflaging Scavenger & Unique Display Invertebrate)

Spider Decorator Crabs (Camposcia retusa) are unique marine crabs from the Majidae family, a group well known for decorating their bodies with material from the surrounding environment. In the wild, this behavior helps them blend into rocky reef, rubble, algae, and sponge-covered habitats. In the aquarium, they may collect pieces of macroalgae, sponge, zoanthids, soft corals, or other small materials and attach them to hooked hairs on their body for camouflage.

This behavior is the main appeal of the species, but it is also the main reason they are considered reef safe with caution rather than fully reef safe. They are not aggressive predators, but they are opportunistic and may disturb corals, loose frags, or small decorative invertebrates while foraging or decorating themselves.

Care Requirements

Care Level: Easy to Moderate – Hardy, but best for aquariums where their decorating behavior can be managed
Minimum Tank Size: 30+ gallons
Aquarium Setup: Requires live rock, caves, crevices, rubble areas, and stable reef parameters

Spider Decorator Crabs do best in mature saltwater aquariums with plenty of rockwork and hiding places. They are often more active at night or in lower-light areas and may spend time tucked into rockwork during the day. Because they may collect materials from their surroundings, they are best kept in aquariums where loose frags, delicate corals, and small sessile invertebrates are secured or not easily accessible.

Diet & Nutrition

Spider Decorator Crabs are omnivorous scavengers that feed on algae, detritus, leftover foods, and meaty items.

Diet: Omnivorous – Eats algae, detritus, leftover food, sponge material, and small meaty foods
Recommended Foods:
Naturally occurring algae and detritus
Leftover fish food
Dried seaweed or nori
Algae wafers
Frozen mysis shrimp
Brine shrimp
Finely chopped seafood
Small sinking carnivore or omnivore pellets

Although Spider Decorator Crabs will scavenge throughout the aquarium, they should not be expected to survive only on scraps. Offering supplemental foods can help keep them healthy and may reduce excessive picking at decorative organisms or coral tissue.

Lifespan & Growth Rate

Lifespan: 2-4+ years with proper care
Growth Rate: Moderate – Can reach several inches across when leg span is included

Spider Decorator Crabs grow by molting and require stable water parameters to molt successfully. After molting, they may hide while their new exoskeleton hardens. Maintaining stable salinity, alkalinity, calcium, magnesium, and trace elements will help support long-term health.

Temperament & Compatibility

Temperament: Peaceful to Semi-Peaceful – Generally non-aggressive, but opportunistic while foraging and decorating
Reef Safe? With caution – May collect, disturb, or attach pieces of soft coral, zoanthids, sponge, macroalgae, or other sessile invertebrates

Spider Decorator Crabs are best suited for peaceful aquariums with secure rockwork and carefully selected tankmates. They should not be kept with aggressive crab predators such as triggers, puffers, hawkfish, large wrasses, large crabs, or other animals that may pick at or eat crabs. In coral-heavy reef aquariums, they should be monitored closely.

Common Challenges & Considerations

Decorating Behavior: Spider Decorator Crabs may attach algae, sponge, soft corals, zoanthids, or other materials to their body.
Reef Safe With Caution: They may disturb corals, small sessile invertebrates, or loose frags while decorating or foraging.
Can Be Nocturnal: They may hide during the day and become more active after lights out.
Needs Stable Rockwork: Their long legs and climbing behavior can disturb loose frags or lightweight decorations.
Opportunistic Feeding: They may pick at weakened organisms, leftover meaty foods, or available organic material.
Molting Sensitivity: Sudden changes in salinity, pH, or alkalinity can cause stress during molting.
Sensitive to Copper: Like all marine crabs, they should never be exposed to copper-based medications.

To prevent issues, acclimate them carefully, provide plenty of hiding places, secure loose corals and frags, feed regularly, avoid copper exposure, and monitor their behavior in reef aquariums.

Water Conditions

Temperature: 72-78°F
dKH Alkalinity: 8-12
pH: 8.1-8.4
Specific Gravity: 1.023-1.025