1 kinds · tap one for a closer look
Territorial and will eat fish and plants; best kept alone with land area.
This one is best kept on its own, or with its own kind.
Territorial and will eat fish and plants; best kept alone with land area.
Not a freshwater tank animal. It needs brackish water or a setup that is mostly land. Read the care notes before you buy.
Good to know: Needs a large land area and burrowing substrate.
Fruit, vegetables, meaty foods and fish.
Tap a food to see what it is.
Common problems. Tap one to see the signs. This is a guide, not a diagnosis.
Egg-bearing with marine larval phase ·
Mates and carries eggs on land, but females must go to brackish or sea water to release the larvae; the larvae need at least about 15‰ salinity (they do best near 25‰) and cannot develop in fresh water.
Not practical at home.
Large paludarium; marine larval rearing.
Gravid female released to seawater.
Hundreds of thousands of eggs.
Planktonic larvae need marine rearing.
A large, colourful land crab from coastal West Africa that digs deep burrows in marshy ground near lagoons and mangroves, reaching down to saline ground water; it cannot stay under water for long.
Dutch zoologist Jan Herklots described this land crab in 1851. Its blue, purple and orange colours made it popular in the pet trade as the rainbow or Halloween crab.
First described by Jan A. Herklots in 1851.
10 facts checked with sources
Invertebrate: land crab (terrestrial decapod crustacean), not an aquarium animal. Cardisoma armatum Herklots, 1851 is accepted in WoRMS. Trade names (moon crab, soapdish crab, patriot crab) are also used for other colourful land crabs (other Cardisoma, Gecarcinus ruricola, G. quadratus), so animals sold as rainbow crab are sometimes a different species (Wikipedia).
WoRMS / DecaNet record: Cardisoma armatum (accessed 2026-10-16) · Wikipedia: Cardisoma armatumNew value. Current DecaNet/WoRMS places Cardisoma in Cardisomatidae; older sources (WoRMS 2018 as quoted by USFWS, Wikipedia) put it in Gecarcinidae (land crabs).
WoRMS / DecaNet record: Cardisoma armatum (accessed 2026-10-16) · U.S. Fish and Wildlife Service (2019): Cardisoma armatum Ecological Risk Screening SummaryCarapace width (crabs are not measured SL/TL). FAO identification sheets (Fischer et al. 1981, quoted by USFWS) give 12 cm maximum carapace width for adult males; legacy 12 cm matches. size-pick: Wikipedia's 20 cm is unsourced and it says captives rarely reach it, so 12 cm is kept.
U.S. Fish and Wildlife Service (2019): Cardisoma armatum Ecological Risk Screening Summary · Wikipedia: Cardisoma armatumNo source states a group size, but adults are aggressive and cannibalistic toward each other; legacy 1 (kept alone) is consistent with this.
Wikipedia: Cardisoma armatumLegacy "s" (semi-aggressive) understates it: adults are aggressive, cannibalistic and eat fish.
Wikipedia: Cardisoma armatumLand crab: aquarium swimming zones do not apply (it should be marked terrestrial / land, not bottom-dwelling). Legacy "b" is misleading.
WoRMS / DecaNet record: Cardisoma armatum (accessed 2026-10-16) · Wikipedia: Cardisoma armatumNew value (legacy had none).
U.S. Fish and Wildlife Service (2019): Cardisoma armatum Ecological Risk Screening Summary · Wikipedia: Cardisoma armatumAbdomen-flap sexing is standard for crabs but no fetched source confirms it for this species. FAO notes unequal claws in large specimens, not a sex difference.
U.S. Fish and Wildlife Service (2019): Cardisoma armatum Ecological Risk Screening SummaryCuesta & Anger 2005 (J. Crustacean Biology 25: 640-654), quoted by USFWS. Supports the legacy marine/brackish larval phase; "not bred at home" is not stated by a source but follows from it.
U.S. Fish and Wildlife Service (2019): Cardisoma armatum Ecological Risk Screening Summary · Wikipedia: Cardisoma armatumSupports the legacy text (large, colourful, West African, needs land and burrowing substrate more than water). Colours fade with age.
U.S. Fish and Wildlife Service (2019): Cardisoma armatum Ecological Risk Screening Summary · Wikipedia: Cardisoma armatum