Common Names: Tricolor hermit, blue-leg hermit, blue-knee hermit, dwarf blue hermit, equal-handed hermit
Range: Tropical western Atlantic Ocean (Florida, the Gulf of Mexico, and the Caribbean)
Natural Environment: These small crabs are found in rocky intertidal zones where they feed upon detritus and algae. They are more active during nighttime than daylight hours.
Water Requirements: Calcium 380 to 430 ppm, alkalinity 2.5 meq/l, pH 8.1 to 8.2, specific gravity 1.023 to 1.025, and a temperature range of 75° to 82°F (24° to 28°C). Keep in mind they cannot tolerate any copper.
There are many small hermit crabs in the aquarium trade, but this hardy species is especially popular with reefkeepers. They are about an inch (2.5 cm) in size and highly suitable for devouring unwanted algae growths such as green hair algae and cyanobacteria. While they do not damage corals, their habit of climbing on almost anything in the aquarium may cause corals to temporarily close.
Stocking level recommendations vary greatly for these little scavengers—usually from 1 to 10 per gallon for reef aquariums. One should consider the condition of the aquarium, however, as very well-maintained systems need only a few in the entire system. Overcrowded and/or overstocked systems no doubt need higher quantities, and new systems probably need none, as hermit nutritional needs will not be met until the aquarium ages somewhat.
Wild Vs. Captivity
Hermits can live about 30 years in the wild, but in aquaria they only last one to two years. Most molting hermits leave the water and bury themselves in the sand for protection from predators. The molting process can occur from once a month to once every 18 months, with the process taking about 10 days to complete.
If the supply of algae is limited, an algae wafer or feeder block may help supplement their diet. They also feed on any uneaten foods that fall to the aquarium bottom.
Because they do not have a shell of their own, they seek empty and suitably sized shells for protection, usually snail shells. The tip of their abdomen is backed into the empty shell. When danger arises, they retract further, disappearing from view. As they grow larger, they must seek slightly larger empty shells. It’s advisable to keep an assortment of different-sized snail shells in the aquarium with any species of hermit, as they are very fussy about their selected shell and are always looking for something better or slightly roomier. In fact, they often enter into battles with other hermits for their shells, with the loser either highly damaged or dead. They may also sometimes pick on live snails, but it is believed they are only seeking the shell and not attacking the snail itself.