Red-leg Hermit Crab, Calcinus californiensis

Red-leg Hermit Crab, Calcinus californiensis. Taken up residence in an abandoned Speckled Cerith Shell, Cerithium maculosum. Photograph taken in Zihuatanejo, Guerrero, December 2018. Photograph courtesy of Ron Woheau, Zihuatanejo.

Red-leg Hermit Crab, Calcinus californiensis. Underwater photograph taken with coastal waters within Parque National Huatulco, Huatulco, Oaxaca, March 2021. Has taken up residence in the abandoned Ornate Nerite Shell, Nerita scabricosta. Photograph courtesy of Marina Sutormina, Stockholm, Sweden.

General information: The Red-leg Hermit Crab, Calcinus californiensis, is a member of the Diogenidae Family of Hermit Crabs. They molt very frequently, from once a month, to once every 18 months and are always in search of new larger shells.  They are sold by the aquarium trade under the name California Scarlet Hermits on a limited basis. In the wild they have life spans of up to 30 years; in captivity they only survive for one or two years.

Identification: They are easy to recognize due to their bright orange-red legs and dark green body colorations. The are a small to medium sized crab with a shell length that is 1.2 cm (0.5 inches) to 1.9 cm (0.75 inches) in length. The left claw (chela) is very large and flattened and orientated obliquely outward. The inside of the fingers on both claws are white, roughly toothed, and have small bristles. The shell and claws are dark green with bright red margins; the walk legs are bright red with black tips and the antennae are orange, the long slender eye stalks are green with a broad white distal band and a black cornea. They use discarded shells for their homes to avoid predation and wave action. Studies have documented that in the greater Guerrero area they can be found in as many as 18 different gastropod shells that vary in size and weight with males being found predominately in differing shells than females.

Habitat and Range: The Red-leg Hermit Crabs are found in groups in the low intertidal and shallow sub-tidal zones over rock and coral structures at depths up to 6 m (20 feet) from the central Sea of Cortez south to Acapulco along the coast of the mainland. They are found in more shallow water environments in the southern part of their range and can be found in a wide variety of shells.

Diet: Red-leg Hermit Crabs are omnivores consuming algae, cyanobacteria and detritus and most active at night.  In turn they are subject to predation by shore birds and invertebrates and are strongly influenced by wave action.

Conservation status:   From a conservation perspective the Red-leg Hermit Crab has not been formally evaluated. However, they are quite common along rock and coral structures and should be considered to be of Least Concern. They are utilized by the aquarium trade at a modest level.