Updated November 05, 2013
If you are looking to add something a little extra to your saltwater tank, consider the hermit crab. Like many crustaceans, hermit crabs serve in the role of a “cleanup crew” in the saltwater tank, sifting through substrate for detritus and eating aquarium algae. In addition their practical benefits, hermit crabs are also very entertaining pets to keep – they can be very active and social which makes them a joy to watch. You do, however, need to be careful about what kind of hermit crab you keep in your tank – not all species are recommended for tanks that house fish or other invertebrates.
About Hermit Crabs
Hermit crabs are a type of decapod crustacean belonging to the superfamily Paguroidea. Though they are called crabs, they are actually more closely related to lobsters than true crabs. Hermit crabs spend most of their lives living in shells but, unlike snails, they do not grow a shell of their own. The hermit crab earned its nickname for its habit of moving from one shell to another – as the crab grows, it must move on to a larger shell. Because they live in shells, it is not often that you see the full body of a hermit crab. They have long spiny legs and claws like lobsters and other crabs with a soft, curling body. The shell provides them with protection for their vulnerable bodies.
In their native habitat, there is sometimes fierce competition over new shells. In some cases, a hermit crab will actually kill a snail or another crustacean simply for the purpose of taking over its shell. The amount of shells available in a given area depends on several factors. First, it depends on the number of other gastropods in the area as well as the number of hermit crabs fighting for the shells. Second, it depends on the number of predators in the area which feed on gastropods while leaving the shells intact. If a hermit crab has a shell that does not fit its size, it will grow slowly and will not be able to move as fast as a hermit crab with a well-fitting shell.
Hermit Crab Tank Requirements
Hermit crabs are naturally found in reef environments and thus have the same tank requirements as many reef-dwelling species. The ideal tank temperature for hermit crabs is between 72 and 78°F with a pH range between 8.1 and 8.4. The specific gravity of the tank should be between 1.021 and 1.028 with kH levels between 150 and 215 ppm. Just as aquarium fish require clean tank water and balanced chemistry levels, so do hermit crabs. If the water quality in the tank is not kept high, your hermit crabs may fail to thrive and they could become susceptible to disease. In addition to healthy conditions, hermit crabs require several inches of sand or loose substrate in which to dig as well as plenty of rock formations to hide in.
Dwarf Red Tip Hermit Crab: These hermit crabs reach a maximum size around 1 inch and they are generally considered to be peaceful. You should, however, add them to your reef tank with caution because large species of fish might view them as prey. Dwarf Red Tip Hermit Crabs are voracious scavengers, feeding on detritus and algae, squeezing into even the smallest spaces in your tank.
Dwarf Zebra Hermit Crab: The Dwarf Zebra Hermit Crab reaches a length of up to 1 inch and it is one of the most popular species for the marine tank. These hermit crabs are named for their black-and-white banded coloration. Despite its small size, this species exhibits a very large left claw which can be used for defense against predators.
Electric Blue Hermit Crab: As suggested by the name, the Electric Blue Hermit Crab is known for its brilliant blue coloration. These hermit crabs grow up to 2 inches long and they are fairly rare. In addition to eating detritus, this species will also eat the green hair algae and cyanobacteria that many fish neglect.
Scarlet Reef Hermit Crab: The Scarlet Reef Hermit Crab grows up to 1 ½ inches long and has bright red legs with a yellow face. This species is very popular, particularly in reef tanks, and it requires very little care. Unlike some species, these hermit crabs are unlikely to cause problems with other tank mates, even small fish.
Other Tips and Tricks
Even though hermit crabs are natural scavengers, likely to feed on detritus and algae in the aquarium, that doesn’t mean that you never have to feed them. Especially if you have more than one hermit crab in your tank, you are likely to need to provide supplemental food. Depending on the species of hermit crab you keep, you will need to offer dried seaweed or some type of meat like chopped fish or Mysis shrimp. You should also stock your tank with an assortment of empty shells so your crabs can move to a different shell when they need to.