Halloween Crab

(Gecarcinus quadratus)

Halloween or not, this crab always sports a brilliant mask that has inspired other nicknames, such as Harlequin Land Crab, Moon Crab, Mexican land crab, and mouthless crab. Halloween Crabs occupy coastal Mexico and Central America and can even be found as far south as Peru. They are forest dwellers, subsisting on leaves and seedlings, and usually feed at night. Despite occupying coastal rainforests and spending most of their time on land, Halloween Crabs must return to the water to lay their eggs. 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 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 upper 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.

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

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. Young crabs forage along the coastline for small particles.

The Halloween crab is an ecosystem engineer. The crabs can occur at high densities, up to 6 per m, 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.

Source: http://online-field-guide.com/Gecarcinusquadratus.html and http://www.environmentalgraffiti.com/news-ten-beautiful-and-bizarre-crabs-0

Quick Facts

Type: Invertebrate.

Diet: Adults eat leaves and seeds; Young crabs forage along the coastline for small particles.

Habitat:  Primarily mangroves and lowland rainforest, often along river banks.

Alternate Names: Harlequin Land Crab, Moon Crab, Mexican land crab, and mouthless crab.

Did You Know? The crab itself is an important food source for raccoons (Procyon lotor) where the species occur together.