Halloween Crab
Gecarcinus quadratus (de Saussure, 1853)

Family: Gecarcinidae - Land Crabs

Order: Decapoda (Brachyura) - Crabs

Class: Crustacea

Phylum: Arthropoda

Kingdom: Animalia

Red List status: Not Listed

Carapace Length: 100 mm, exceptionally to 250 mm

Halloween crab. Rio Claro Biological Preserve, Costa Rica

The Halloween crab occurs in near-coastal areas from the Gulf of California in Mexico as far south as Colombia.

Range            Description            Habitat            Behaviour            Biology            Ecology            References
Other common names: Moon crab, harlequin land crab, Mexican land crab, mouthless crab



The Halloween crab has an apparently completely black (actually dark brown when examined closely) upper carapace, a bright orange-red body and limbs and purple claws. Two bright yellow to white, triangular ‘eyes’ decorate the front of the upp

Gecarcinus quadratus. Rio Claro Biological Preserve, Costa Rica. Note the white spots towards the rear of the carapace.

er carapace, while there are two white spots at the rear of the carapace.

Similar species: The patterning of this crab is unique, particularly the combination of purple claws and orange-red limbs. It is sometimes mistaken for Gecarcinus lateralis; this species has whitish to orange-red claws and the upper carapace is rimmed with the same colour. Gecarcinus ruricola has darker, purple limbs and a purplish carapace without 'eyes'. Neither species possesses white spots at the rear of the carapace.



Primarily mangroves and lowland rainforest, often along river banks. This species is dependent on habitats with readily available sources of freshwater, to prevent desiccation of its lungs. In southern Costa Rica, the crab can be found up to 600 m inland.



A principally fossorial land crab, active during the daytime and most commonly encountered following heavy rain. During the wet season, crabs migrate to the coast in large numbers to spawn.

Diet: Adults eat leaves and seeds, removing them from the surface and hoarding them in their burrows. By doing they play an important role in structuring forest habitat where they occur (see Ecology). Young crabs forage along the coastline for small particles.



Life cycle: The planktonic stage in this species lasts for at least a month, following which young crabs settle and develop in coastal habitats.



The Halloween crab is an ecosystem engineer. The crabs can occur at high densities, up to 6 per m-2, and the removal of large quantities of leaf litter from forest topsoils influences carbon storage and nutrient cycling, reducing the carbon and mineral content of the topsoil and enriching lower soil layers. The species preferentially feeds on the seeds of particular types of plant, favouring the persistence of some at the expense of others. These mechanisms have the overall effect of reducing tree density and diversity in forests where the crab occurs. Crab burrows established near the ocean during the breeding season may also provide breeding grounds for mosquitoes once abandoned. The crab itself is an important food source for raccoons (Procyon lotor) where the species occur together




Arachnoboards: Moon crabs?

Effects of the Land Crab Gecarcinus quadratus on Floristic Diversity of a Neotropical Rainforest at Sirena Biological Station, Corcovado National Park, Costa Rica
Marine Invertebrates of Guana Island

Brusca, R. C., Common intertidal invertebrates of the Gulf of California. Univ. Arizona Press, 2d. Edition.Tucson.1980.513 p
Hendrickx, M. E. (1983) Studies of the coastal marine fauna of southern Sinaloa, Mexico. II. The decapod crustaceans of Estero el Verde. Anales del Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autónoma de México
Sherman, P.M. (2006) Influence of land crabs Gecarcinus quadratus (Gecarcinidae) on distributions of organic roots and carbon in a Costa Rican rain forest.
Revista de Biología Tropical 54: 149-161