🐾 LandCare difficulty: IntermediateLegal complexity: Low
Halloween moon crab
Gecarcinus quadratus · also called Halloween crab, Moon crab, Harlequin land crab, Mouthless crab
A spectacularly coloured land crab from Central American coasts, with a deep purple-black body, orange legs and yellow eyespots. It is almost entirely terrestrial, needing a warm, humid setup with deep substrate plus BOTH a fresh and a brackish water dish — not a fully aquatic tank, and never salt water alone, which it cannot survive on.
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Quick facts
| Size | Carapace about 5 cm wide; leg span up to roughly 11-12 cm |
| Lifespan | 5–10 years |
| Social needs | group |
| Native region | Pacific coast of Central America (Mexico to Panama) |
| Origin | New World |
| Climate | 🌴 Tropical |
| Water type | 🌫️ Brackish |
| Family | Gecarcinidae |
| Genus | Gecarcinus |
Part of the Freshwater crabs
Small crabs kept in aquariums and paludariums. Some, like the Thai micro crab, are fully aquatic, while many others (such as the red claw crab) are brackish and semi-terrestrial, needing both water and a dry land area to climb out and breathe air.
Habitat & space requirements
From the minimum an animal needs to be kept humanely, up to the ideal setup. Bigger is almost always better — minimums are floors, not targets.
Life & growth stages
How this animal changes through its life — each stage often has its own care, diet and space needs.
Habitat & enclosure
Keep as a primarily terrestrial crab in a tall, humid terrarium with a deep moist substrate for burrowing. A 60 cm / 20 gallon tank suits one or two; allow more floor space for a small group. Maintain 24-28 C and high humidity (70-80%) with good ventilation to avoid stagnation. Provide a shallow dish of dechlorinated fresh water and a separate dish of brackish water (marine salt to ~1.005-1.010) so the crab can osmoregulate and wet its gills; both must be shallow and easy to climb out of. Importantly, it cannot survive on sea water alone — it needs constant access to fresh water and only sips brackish to balance its salts. Add cork bark, caves and sturdy climbing wood. A very secure, gap-free lid is essential — they are strong climbers and persistent escapees.
Substrate
Use a deep (10-15 cm) burrowable substrate such as a coconut-fibre and play-sand mix (often 5:1), kept moist enough to hold a tunnel without being waterlogged. Sphagnum moss and leaf litter on top help retain humidity and provide grazing. The depth must let the crab fully bury itself to moult safely.
Equipment & setup
Needs a heat source to hold 24-28 C (under-tank heater or low-watt overhead, monitored by thermostat), a hygrometer and thermometer, regular misting or a humidity system, two shallow water dishes (fresh and brackish), marine salt and a hydrometer, and a heavy escape-proof lid. No UVB requirement, but a gentle day/night light cycle is beneficial. Good cross-ventilation prevents mould.
Diet
Omnivorous scavengers. Offer a varied diet of leafy greens, fruit (mango, apple, banana), vegetables, plus protein from fish, dried shrimp, bloodworm, the occasional bit of cooked meat or commercial crab/hermit-crab food. Provide cuttlebone or a calcium source for moulting and a steady supply of leaf litter and decaying wood they will graze. Feed every day or two and remove spoiled food promptly.
Behavior & temperament
Nocturnal and shy, spending daylight burrowed or hidden; activity peaks at night and they can dig burrows up to a metre or more deep. Generally peaceful with their own kind and can be kept in small groups given space and multiple hides, though they may compete over burrows. They can deliver a sharp pinch and will autotomise (drop) a limb if grabbed, so they are best treated as a display animal with minimal, gentle handling. They are sensitive to vibration and bright light and will dash for cover.
Health
Moulting is the most dangerous time — they bury to moult and must not be disturbed; provide deep damp substrate, calcium and both fresh and brackish water for a successful shed, and leave the cast shell to be eaten. Dehydration and low humidity cause gill damage and death, while chronically wet, stagnant conditions cause shell rot and fungal infection, so balance humidity with ventilation. Avoid copper and insecticides. Note that wild-caught imports are common and may arrive stressed or with regenerating limbs.
Tips, DIY & hacks
Provide BOTH a fresh and a brackish water dish — access to fresh water is essential and the crab cannot live on salt water alone, sipping brackish only to balance its salts. Make the substrate deep and damp so the crab can burrow to moult, and never dig out or disturb a buried crab. Lock the lid down; these crabs escape through surprisingly small gaps. Quarantine wild-caught imports, keep humidity high with ventilation to avoid both dehydration and shell rot, and offer plenty of calcium.
Sources
- Gecarcinus quadratus — Wikipedia (reference)
- Halloween Moon Crab — Detailed Guide: Care, Diet, and Breeding (care guide)
- Wikipedia: Halloween moon crab (wiki)