Spider Decorator Crab – Camposcia retusa

Overview:
The Spider Decorator Crab is a small-to-medium marine crab that camouflages by attaching algae, sponges, and other soft material to hook-like hairs on its shell and legs. It does best in a mature saltwater aquarium with stable parameters and plenty of live rock, crevices, and shaded areas. Provide moderate water flow (enough to keep detritus from settling, but not so strong it constantly dislodges its camouflage) and strong filtration, since it is an active scavenger. Aim for 24–26 °C (75–79 °F), salinity 1.024–1.026, pH 8.1–8.4, and consistent alkalinity and calcium to support clean molts. Because it relies on camouflage, include safe “decor” options: macroalgae, rubble, and non-stinging soft growth; avoid sharp fragments that can snag limbs or eyes.

Compatibility:
Generally peaceful, but opportunistic. It is safest with calm community reef fish that won’t harass crabs. Avoid triggers, puffers, hawkfish, larger wrasses, and other crab-eaters. With sessile invertebrates, expect risk: it may carry pieces of soft corals, zoanthids, or sponges as camouflage and can irritate or damage them, and it may nip at fleshy polyps. It can also prey on very small shrimp, tiny snails, and weakened or freshly molted tankmates. Keep it with robust cleanup-crew species, larger snails, and non-aggressive crabs only if the tank has ample space and hiding sites.

Health and Quarantine:
Most problems trace back to stress and poor molting. Provide stable salinity and temperature, adequate calcium/alkalinity, and hiding places for pre-molt and post-molt periods; do not disturb it during a molt. Missing legs can regrow over successive molts if conditions are good. Avoid all copper-based medications and contaminated equipment. Quarantine for 2–4 weeks in an invert-safe system with matching salinity, live rock or PVC shelters, and close observation for injury, lethargy, or failure to feed. Use slow drip acclimation to prevent osmotic shock.

Omnivore

Algae Meaty Foods Coral Tissue
Spider Decorator Crabs are slow, deliberate scavengers that spend much of their time searching for materials to attach to their bodies for camouflage. This natural decorating instinct leads them to pull algae, sponge, and occasionally small bits of coral tissue to blend into their surroundings. They are generally peaceful toward fish and mobile invertebrates, but their decorating behavior can make them unsuitable for coral-heavy systems. Most activity occurs at night, when they quietly roam rockwork and sand in search of food and new materials to add to their disguise, remaining reclusive and unobtrusive during the day.

FAQ

Frequently Asked Questions

About the Spider Decorator Crab

  • My Spider Decorator Crab is pulling pieces of sponge and algae off my rockwork. Is it eating them or decorating itself?
    In most cases, it is decorating itself. Spider Decorator Crabs instinctively attach soft materials to their shells for camouflage. They may remove bits of sponge, algae, or loose coral tissue to blend into their surroundings. This is normal behavior, not a sign of aggression. If you want to reduce how much live material they pull, offer small pieces of macroalgae or artificial decor they can use instead.
  • I rarely see my Spider Decorator Crab during the day. Is it supposed to hide this much?
    Yes. Spider Decorator Crabs are naturally cryptic and rely on camouflage to avoid predators. They spend most of the day tucked into rock crevices and become more active after lights dim. This is completely normal. If you want to spot them more often, use a red flashlight after dark; they do not detect red light easily and remain out in the open.
  • Will a Spider Decorator Crab bother my corals?
    They do not typically eat healthy coral tissue, but they may remove small loose fragments or soft materials for decoration. They also sometimes step across corals while navigating rockwork, which can cause polyps to retract temporarily. Most tanks handle this minor interaction well, but delicate single-polyp corals or freshly glued frags may need extra protection.
  • My Spider Decorator Crab is carrying so much material that it can barely move. Should I remove some of it?
    No. The crab controls its own decoration load and will adjust it naturally during molts. Carrying a heavy covering is part of its defense strategy, and removing decorations can stress the crab by exposing it visually. After a molt, it will rebuild a new set of decorations that are better suited to its size.
  • Is it normal for my Spider Decorator Crab to pick at polyps or soft coral edges?
    Light picking can happen, especially if the crab is hungry or looking for material to attach to its body. This is usually not predatory but opportunistic. To prevent this, ensure the crab is fed small meaty foods several times per week and has access to spare natural materials like macroalgae trimmings. When well-fed, they largely ignore coral tissue.