Gecarcinus quadratus

[Ulli Bauer]

Text: Monika Rademacher
Fotos: Oliver Mengedoht


More pix: http://www.panzerwelten.de/v/Gecarcinus/quadratus/

Scientific name: Gecarcinus quadratus

Trivial names: Halloween Crab, Mouthless Crab, Mexican Land crab, Harlequin Land Crab

Systematics: Domain: Eucaryota, kingdom: Animalia, subkingdom: Metazoa (multiple-celled animals), Eumetazoa (true tissue), grade: Bilateria, branch: Protostomia, infrakingdom: Ecdysozoa (molting animals), phylum: Arthropoda (jointed-leg invertebrates), subphylum: Crustacea, class: Malacostraca (higher crustaceans), superorder: Eucarida, order: Decapoda (ten-legged crayfish), suborder: Pleocyemata, infraorder: Reptantia, section: Brachyura (true crabs), superfamily: Grapsoidea, family: Gecarcinidae (land crabs), genus: Gecarcinus, species: Gecarcinus quadratus

Origin/distribution: Pacific coast from Mexico to Peru, Atlantic coast from Florida to Guyana.



Description: Black carapace with white dots and orange spots (at the front, two by the eyes and on the back), the rest of the body and the legs are orange, purple claws, white-tipped.

Sex differences: Typical for crabs, the males have a narrow, pointed abdominal apron, the female's apron is wide and rounded; moreover, the female's claws are smaller.



Males (left) have a narrow abdominal apron…


…females a wider one.

Size: up to 10 cm carapace width (there have been reports about exceptional 25 cm)

Life span: at least 10 years

Temperature: tropical (20 to 28 °C).

Tank size/stock: In a 1 meter long tank a pair to four specimens (given that the tank is well-structured!)

Tank decoration: Terrarium with sand and maybe terrarium humus for burrowing, things to hide and climb on (wood, rocks), moss, nonpoisonous plants (e.g. no ivy), tree leaves (as hideout and food). A small water part (with fresh, brackish or sea water) is possible, but not necessary. A small bowl with water or a little fountain are as good as spraying the terrarium with water from time to time. These land crabs do not need access to water! They take the humidity they need from moist substrate and actually avoid water!



Food: Typical for crabs, they are omnivores.
• Leaves (the main staple of many crabs in nature; mostly oak and beech are fed, however, all European broadleaved tree leaves are possible, also Indian almond leaves), muck, water plants
• Vegetables/fruit: nearly all vegetables and fruit are suitable (peas, lettuce, cucumber, apple, zucchini, pear, banana, grapes, tomato, Brussels sprouts, bell peppers) except for parsley and beans or other kinds that contain Prussic acid or copper; carrots (boiled); potato and rice (boiled) or noodles (uncooked? Don't leave these in the tank for too long a time though, they can be the cause of turbid water and finally lead to a bacteria bloom and oxygen depletion); no citrus fruit due to their high acid content
• Dry food: Catfish tabs, fish (flake) food, food pellets, rabbit, guinea pig and chinchilla food pellets (without copper!), Spirulina tabs, crayfish tabs, Gammarus
• Frozen food: Black, glass and blood worms, Cyclops, brine shrimp, clam meat
• Live food: Earthworms (it's best to cut them into pieces though, or else these worms might burrow in the substrate, possibly also under water, die and rot there unnoticed until it's too late)
• Meat (rarely): Chicken bones with meat rests (rinsed well to prevent too much fat from getting into the terrarium)
• Fish: deep-frozen smelts et.al., tuna fish, sardines, herring etc. fresh or from a can (in their own juice, not in oil)
• Calcium: cuttlebone, smashed eggshells or powdered calcium in self-made food sticks

Behavior: Not very aggressive towards conspecifics, often sit in their burrows or caves for hours or even days, like to burrow (not down to the ground water). Diurnal, in the presence of many predators nocturnal, not during the rainy season (in nature).



Reproduction: Seasonal mating. The larvae are released into the sea after about three weeks and need at least a month there to grow to small crabs, going through several zoea and megalopa stages, then return to land. They tolerate a salinity of 50 to 125%, roughly 15 to 40 g of salt per liter. They have already been bred in the laboratory.
Young crabs search the waterline on the shore for small food particles.

Socialization: said to be possible with G. lateralis (also called Halloween Crab)


A Gecarcinus quadratus is climbing around on a G. lateralis undisturbedly.

Additional information:
• In nature, they live in neotropical coastal and rainforests near the shore and are found at places at least 600 meters upcountry. Sometimes also on riversides and in sand dunes. Up to six burrows (50 cm to 1 meter deep) per square meter.

• Principally herbivore in nature, mainly eats saplings and leaves. Leaves are drawn into the burrow where their carbon-nitrogen ratio changes due to the rot process.

• They are land crabs, the most terrestrial of all. Adult animals spend their entire life on land. In nature, they live up to 30 km away from the sea and at heights of over 300 m. They have adapted to life on land so much that they even drown in water and only take to the sea shore for releasing their larvae. This is the result of their significantly smaller gill surface (only 15% of that of aquatic crabs) that thus cannot take up enough oxygen any more in the water (only 1/6 to 1/7 of the air's oxygen content).

• Before and after molting, these crabs retreat to their burrows for a period of up to several weeks and don't eat and are, all in all, very inactive. In nature they eat the empty exuvia in their burrow in order to get the calcium they need for forming a new carapace. After molting, crabs, like all crustaceans, are quite soft ("soft crayfish") and need time without being disturbed in order to let their new carapace harden entirely. In order to prevent conspecifics from injuring them they thus need sufficient places to hide. When molting, these animals can - like all crustaceans - replace lost or self-amputated limbs.

• G. quadratus do not compare to Cardisoma regarding their aggressiveness or their territoriality, i.e. they can easier be kept in groups and it is not compulsive to keep them alone in a tank. However, carapace widths of up to 9 cm are accounted for, thus an adult crab can easily reach a legspan of nearly 30 cm, this should always be kept in mind when choosing the tank. The better the terrarium is structured (many hideouts and possibilities to burrow, several levels, moss, leaves, wood etc.), the more animals can be kept in it. As a guideline you take two to four of these crabs to a 100 cm long tank, whereas the number of females should always exceed that of the males

• As all crabs, Gecarcinus quadratus are good climbers, thus the terrarium cover has to close off the tank securely.


These crabs are usually very secretive.