Hermit crabs are probably one of the most popular animals that are kept by marine hobbyists, since there are many different sizes and types available. It is the rare marine aquarium that does not have at least a few hermit crabs, and the larger hermit crabs are often kept as the focus of an aquarium just for them, perhaps with a few fast and hardy fish.

Types of Hermit Crabs as “Cleanup Crew”

Small hermit crabs are often thought of as “janitors” or part of the “cleanup crew” for marine tanks. Usually the small hermits offered for sale go by common names such as blue legs, red legs, or scarlets. They are all collected wild throughout all of the tropical and temperate seas, reefs and beaches, and they represent various genera and species. The most common small hermits in the hobby are from the genera Clibanarius, Calcinus, or Paguristes and which exact species they are really doesn’t much matter. All of these hermit crabs stay small and will eat algae and tiny pieces of leftover food. They can be seen constantly crawling around the tank, probing into small crevices and openings in the décor and picking at nuisance algae.

All of these small hermit crabs are considered pretty much reef-safe, meaning that they will not bother prized specimens of corals, clams or other inverts. Sometimes hobbyists get upset when the cleanup crew eliminates what was considered decorative algae on the live rock, but other than that there are normally not any problems with the small hermits in reef tanks. The typical rule of thumb is to have one small hermit crab for each gallon of water in the tank, but that can sometimes be too many, depending on how heavily the tank gets fed.

Care and Feeding

When it comes to the care and feeding of small hermit crabs it is really not sufficient to assume that they are getting enough to eat simply by their scavenging. I have always made sure that small pieces of spirulina wafers made it down to the bottom of the tank for the hermits, and that when the tank itself was fed there were, in fact, some leftover foods that made it down for the hermit crabs. In most types of marine tanks there will be enough leftovers that the hermit crabs will get plenty to eat. However, in the very low nutrition levels and pristine water quality of some of the more advanced reef tanks there will not be much of anything for the hermit crabs to eat; in these cases it is very important to make sure they get some food. Most of the time the availability of shells is a more important factor in keeping these small hermit crabs than availability of food. As they grow and molt, hermit crabs are always looking for new and usually larger shells. Sometimes you will see two crabs fighting over a shell, which is very interesting to observe. If there are no appropriate shells available for a newly molted/molting hermit crab, they have been known to kill snails to get the shells. It’s a good idea to have many shells, of different sizes but especially larger ones, kicking around the tank for any hermit crab that wants a new one.

“Specimen Tank” Hermit Crabs

The larger hermit crabs can make very interesting inhabitants of a tank devoted to them alone, or with other fish and invertebrates that are fast and clever enough not to become a meal for the hermit crab. The most interesting hermit crab to keep is by far the “decorator” or “anemone carrying” hermit crab (Dardanus pedunculatus). These animals walk around in a shell to which they have attached certain small anemones, and sometimes pieces of macroalgae. I once watched as one moved from one shell to another. The process began with the typical feeling around of the new shell, the fast move from the old shell into the new one, and the grasping onto the old shell just in case the fit wasn’t right. Once the crab decided that it liked the new shell, it methodically peeled off the anemones from the old shell and placed them on the new one.

Some of the larger regular hermit crabs can also make interesting specimen tanks, as long as you are prepared for their rearranging everything in the tank. I have seen hermit crabs about the size of a small fist, walking around in good-sized conch shells. As can be imagined, they move around anything that isn’t permanently attached in the tank. The larger hermit crabs are very interesting – you just have to be careful about what you put with them for tankmates and decor.

Article Summary

• Small hermit crabs make up an important part of the cleanup crew for any marine
aquarium
• The most common types are blue legs, red legs and scarlets
• Usually reef-safe, it is important to make sure that the hermit crabs are getting
enough to eat
• Have plenty of extra empty shells, as they are always looking for newer and
slightly larger quarters

Land Hermit Crabs

In addition to the hermit crabs that are kept in marine tanks, land hermit crabs make excellent pets. In many ways they are like a Siamese Fighting Fish (Betta splendens) in that they can be kept in a fairly small space and that they are often kept alone, although they can be kept in groups. Land hermit crabs are very hardy, with minimal care required, and kids absolutely love them.

Land hermit crabs are found all over the world, but the ones usually kept in the hobby are Coenobita clypeatus and Coenobita compressus, which are native throughout the Caribbean. There are a few primary suppliers of land hermit crabs to the industry, and the creatures are available in all kinds of “homes”. Besides the natural shells, there are also “shells” that are little football helmets in the livery of each professional football team, and many college teams. In spring there are baseball caps as shells, and for major holidays such as Christmas and the Fourth of July there are “theme” shells.

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SOURCES
In addition to my own experience, for this article I spoke with:
Brett Varnum Co-owner with his sister, Bethany Stockman
Laconia Pet Laconia, NH 603.524.8311
Steve Richmond Owner Lovely Pets
Quincy, MA 617.786.1898?