I should start by saying that I, as well as others on the message boards, have mixed feeling on crabs. Some people will say they are the devil's spawn, while others will say they are great and have had no problems, and you will find some online 'packages' that consist mostly of (hermit) crabs. You may have to experiment with them, and form your own opinions. Some crabs of the same species will act differently, as far as aggression, or nipping at corals. You may have to test the waters and see how yours reacts. I think that they just need to be monitored to see what kind of behavior they exhibit.
I am including many crabs below, but from what I have seen, the most commonly used and readily found, are the Emerald Crab, the Blue or Red Leg Hermits, the Zebra hermit, and the Scarlet Reef hermits.
Emerald (mithrax):
The Emerald crabs are great cleaners, and hard workers. Mine is at constant work, always picking at the rock and keeping things cleaned up. It pulled all the filamentous dead junk off the rock, and cleaned down in nooks and crannies. Emerald Crabs can be hit or miss when finding one that will nip at your corals. I ended up returning one of mine to the local fish store (LFS) when I saw him pulling off some zoanthids. Many people find that they don't touch their corals and work just fine. I may end up adding more down the road, as they are such good cleaners in my opinion.
The Emerald Mithrax Crab is well respected for its scavenging ability. It will enthusiastically feed on uneaten meaty foods and many types of nuisance algae. Unlike many other animals, Mithrax sculptus will eat bubble algae and helps clean your aquarium of these algae. Its distinct, flat shiny green body and hairy legs easily identify the Emerald Mithrax Crab. Native to the reefs of the Caribbean, the Emerald Mithrax Crab is nocturnal and hides in caves and amongst rubble during the day. In the home aquarium, this member of the Majidae family requires a well-established aquarium with plenty of rockwork and hiding places. Once familiar with its surroundings, the Emerald Mithrax Crab will venture out of hiding during the day to forage on algae.
Care needs to be taken to ensure an ample supply of food is available for the Emerald Mithrax Crab. Many aquarists supplement the Emerald Mithrax Crab's diet with dried seaweed and chopped meaty foods, such as shrimp, as well as a quality pellet fish food.
Otherwise, this opportunistic feeder may turn to corals, invertebrates, or small fish for a food source. However when well fed, most Emerald Mithrax Crabs are very tolerant of their tankmates and highly compatible in reef environments. Like other invertebrates, the Emerald Mithrax does not tolerate copper-based medications or fluctuating water parameters.
Care needs to be taken to ensure an ample supply of food is available for the Emerald Mithrax Crab. Many aquarists supplement the Emerald Mithrax Crab's diet with dried seaweed and chopped meaty foods, such as shrimp, as well as a quality pellet fish food.
Otherwise, this opportunistic feeder may turn to corals, invertebrates, or small fish for a food source. However when well fed, most Emerald Mithrax Crabs are very tolerant of their tankmates and highly compatible in reef environments. Like other invertebrates, the Emerald Mithrax does not tolerate copper-based medications or fluctuating water parameters.
Blue Legged Hermits:
This is one crab that I have mixed feelings on. They seem to clean well as they are always picking at the rocks, and I have watched them eat diatom off the substrate. But I have also seen them fight with each other, and I had one that killed one of my Nassarius Snails just to get his shell. You will need to keep several larger sized empty shell for the hermits to move into, as they outgrow their current shells or they will result in killing a snail possibly. It is amazing to watch, as I have one of my blue legs in his original tiny shell, that has hardly grown. And another one that was his same size when I first got them, that took over a shell that was too big for him at the time, and now has a body about 3 or 4 times bigger than the one that hasn't moved up in shell size yet. Quite amazing to watch the growth rate of them according to what shell they might be in.
Don't let the small size of the Dwarf Blue Leg Hermit Crab fool you. As a voracious scavenger, this omnivore can get into the smallest crevices and openings within live rock to consume nuisance algae including hair algae and cyanobacteria. While doing so, Clibanarius tricolor also helps aerate sand substrate, thereby encouraging growth and activity of beneficial bacteria. Also known simply as the Blue Leg Hermit Crab, this member of the Diogenidae family is a colorful and reef-safe addition. Named after its bright and colorful red-banded blue legs, the Blue Leg Hermit Crab has claws of equal size and makes its home in abandoned snail shells. Take note that when the Dwarf Blue Leg Hermit Crab is looking for a new home or if food supplies are insufficient, this minute scavenger may attack snails to obtain the shell for its home or eat the snails for food.
Supplement the diet of the Dwarf Blue Leg Hermit Crab with dried seaweed if insufficient algae are present. Though an efficient scavenger, and due to its small size, the Dwarf Blue Leg Hermit Crabs should be kept in groups for larger aquarium systems.
Supplement the diet of the Dwarf Blue Leg Hermit Crab with dried seaweed if insufficient algae are present. Though an efficient scavenger, and due to its small size, the Dwarf Blue Leg Hermit Crabs should be kept in groups for larger aquarium systems.
The Dwarf Red Tip Hermit Crab is a voracious scavenger. Like its Blue Leg cousin, the Dwarf Red Tip Hermit Crab serves as an ideal member of your marine or reef aquarium's cleanup crew. Also known simply as the Red Tip Hermit Crab, this omnivore will scavenge all over your live rock and sand substrate - finding its way into the tightest of spaces - to feed on algae and detritus. Like other members of this genus, the Red Tip Hermit Crab has claws of equal size and, for this reason, members of this genus are sometimes called "Equal-handed Hermit Crabs." Native to the coastal water surrounding Mexico, the Red Tip has a bright red face and legs. In the home aquarium it does best in saltwater reef or fish-only systems with sand substrates in which they can forage and dig. Its feeding methods also help aerate the sand bed and promote the growth of beneficial bacteria. The Dwarf Red Tip Hermit Crab should ideally be kept in a well-established system with plenty of algae and live rock to graze upon.
Making its home in abandoned snail shells of various size and shape, be sure to offer empty shells to accommodate the growth of these small members of the Diogenidae family. Additionally, offer dried seaweed if algae levels are insufficient. Like other invertebrates, care needs to be taken during the acclimation process to prevent pH shock. Also, take special care to ensure an invertebrate-friendly environment free of predators and copper-based medications.
Making its home in abandoned snail shells of various size and shape, be sure to offer empty shells to accommodate the growth of these small members of the Diogenidae family. Additionally, offer dried seaweed if algae levels are insufficient. Like other invertebrates, care needs to be taken during the acclimation process to prevent pH shock. Also, take special care to ensure an invertebrate-friendly environment free of predators and copper-based medications.
This is one Crab that many people find to be more peaceful, and get along well with other tankmates. Some call them lazy though, but I have found mine to be decent workers, cleaning most of the time, and spends a fair amount of time on the substrate, cleaning each grain of sand, one by one. It does a good job at keeping the rocks and the substrate clean.
It is easy to see why the Scarlet Reef Hermit Crab is one of the most popular reef maintenance animals. Paguristes cadenati is very hardy and requires minimal care in a well-established system. More importantly, however, these small hermit crabs have a voracious appetite for detritus and algae. In fact, they are particularly fond of nuisance algae of the filamentous, hair, and slime varieties, as well as cyanobacteria. Finally, unlike some hermit crabs, most Scarlet Reef Hermit Crabs are very peaceful towards their tankmates. Also known as the Red Reef or Red Legged Hermit Crab, the Scarlet Reef Hermit Crab is named for its bright red legs, which are contrasted by their yellow face. Native to the reef faces and coral rubble of the Caribbean and Western Atlantic, these active scavengers can consume large amounts of animal matter and algae. Despite their large appetites and constant feeding habits, the Scarlet Reef only grows to an adult size of 1-1/2" in length.
In the home aquarium, Paguristes cadenati is best kept in an established reef system with ample algae supplies. However, they will eat almost anything, including fish food and invertebrate diets. If algae levels are insufficient, supplement their diet with dried seaweed and other marine foods.
Like other hermit crabs, an ample supply of empty shells should be available for the Scarlet Reef Hermit Crab to move into as they molt and grow. As with all invertebrates, they do not tolerate copper-based medications and extreme fluctuations in water parameters. Also, take special care to ensure an invertebrate-friendly environment free of predators.
In the home aquarium, Paguristes cadenati is best kept in an established reef system with ample algae supplies. However, they will eat almost anything, including fish food and invertebrate diets. If algae levels are insufficient, supplement their diet with dried seaweed and other marine foods.
Like other hermit crabs, an ample supply of empty shells should be available for the Scarlet Reef Hermit Crab to move into as they molt and grow. As with all invertebrates, they do not tolerate copper-based medications and extreme fluctuations in water parameters. Also, take special care to ensure an invertebrate-friendly environment free of predators.
Zebra Hermit:
The Dwarf Zebra Hermit Crab is one of the most popular hermit crabs for the home marine aquarium. It gets its name from its distinct coloration. Calcinus laevimanus is named for its black and white pincers and the white bands that dress its otherwise dark legs. Like other members of the genus Calcinus, the Dwarf Zebra Hermit Crab also has long eyestalks. However, this particular crab's eyestalks are a brilliant blue and fades into an orange-tinged upper half. Also known as the Hawaiian Reef or Left-Handed Hermit Crab, the Dwarf Zebra Hermit Crab is very small but boasts an enlarged left claw. If attacked by a predator or threatened, the Dwarf Zebra Hermit Crab backs into its shell and uses the large left claw to block and defend the entrance to its shell. The Dwarf Zebra is found in the inter-tidal areas across the Indo-Pacific from Africa to Australia to Hawaii.
Since they scavenge for detritus and consume nuisance algae, including red slime algae (cyanobacteria), the Dwarf Zebra Hermit Crab is a highly desired addition to the home reef aquarium. If there are insufficient algae in the aquarium, their diet should be supplemented with dried seaweed. Like other invertebrates, care needs to be taken with the use of medications. Additionally, strict water parameters must be maintained. Be sure to accommodate their growth by supplying empty shells of various size and shape.
Since they scavenge for detritus and consume nuisance algae, including red slime algae (cyanobacteria), the Dwarf Zebra Hermit Crab is a highly desired addition to the home reef aquarium. If there are insufficient algae in the aquarium, their diet should be supplemented with dried seaweed. Like other invertebrates, care needs to be taken with the use of medications. Additionally, strict water parameters must be maintained. Be sure to accommodate their growth by supplying empty shells of various size and shape.
Halloween Hermit:
I have not had one of these personally, but see them at many LFSs and online occasionally. Very bright and colorful crabs.
The Halloween Hermit Crab, with its vibrant orange and red banding, stands out as a member of your aquarium cleanup crew. Originating from the Hawaiian Islands, the Halloween Hermit Crab boasts attractive color variegation and is a beautiful accent to the marine aquarium. The Halloween Hermit Crab is a very useful aquarium cleaner that helps maintain a healthy aquarium environment by eating any left over food that may settle on the substrate. Adding further value, the Halloween Hermit Crab is known to efficiently eat algae including green hair algae and cyanobacteria. It also provides a valuable service of aerating aquarium substrate by sifting through the sand. Be aware that as the Halloween Hermit Crab attains a large size, this lumbering scavenger may disrupt rockwork or corals in reef aquariums. The Halloween Hermit Crab lives in abandoned snail or triton shells and may resort to attacking and eating a snail so it can use the shell for its home. To prevent this from happening, provide the Halloween Hermit Crab empty shells of assorted shapes and size.
If there is an insufficient amount of algae present, the Halloween Hermit Crab will need to be fed dried seaweed, as well as meaty items such as mysis shrimp.
If there is an insufficient amount of algae present, the Halloween Hermit Crab will need to be fed dried seaweed, as well as meaty items such as mysis shrimp.
A few others that I have no experience with, but wanted to mention:
Sally Lightfoot:
The Sally Lightfoot Crab is also known as the Nimble Spray, Short, or Urchin Crab. It has a brown body, with orange to yellow rings on the legs. It actually belongs to a family of shore crabs, however, it is less likely than the other genera to go on land. Its carapace is very flat. which allows it to hide in small crevices within rock work. It prefers a strong current and will require a large aquarium with large amounts of rock work where it can hide and scavenge for detritus. It will also eat algae. When large, it can become aggressive and catch and eat small invertebrates and fish.
If insufficient algae is present, its diet may need to be supplemented with dried seaweed. Meaty items should also be offered.
If insufficient algae is present, its diet may need to be supplemented with dried seaweed. Meaty items should also be offered.
Note by melev: Sally Lightfoot crabs have a 50/50 reputation of being problematic in your reef tank. They are scavengers for a reason, and move swiftly to the point they could catch unwary smaller fish. With odds like those, I've chosen not to keep any in my systems.
Arrow Crab:
The Arrow Crab, also known as the Spider Crab, has extremely long legs. It is called the Arrow Crab because of the shape of the body and head. The size is variable, many reaching six inches, and some up to 10 inches. Females may be dramatically smaller. Different species inhabit different parts of the world. The most common Arrow Crab (Stenorhynchus seticornis) comes from the Caribbean, but other species are imported from the Indo-Pacific region, eastern Africa, and California. They normally inhabit portions of the reef usually associated with a small cave or crevice. It is a hardy, long-lived invertebrate, that can be housed in the reef aquarium. This crab has been known to attack crustaceans such as Banded Coral Shrimp, and may even attack small slow moving fish. All crabs are opportunistic feeders and if insufficient food is present they may pick at mushrooms or polyps searching for food. Breeding Arrow Crabs in the aquarium is not generally successful. Larvae are free-swimming and hatch in about two weeks. It will accept almost all meaty, flake and tablet foods.
Note by melev: Arrow crabs will consume Bristleworms. If your tank seems to have too many present, this crab will help cull the more visible ones, but it will not erradicate them entirely. It's a nice addition to the tank that tends to be out during the light period.
Porcelain Crab:
The Porcelain Anemone Crab is white with red spots and/or blotches of red or brown. They have very large front claws which they use to fend off potential predators. They are peaceful, and make a wonderful addition to any reef or invertebrate aquarium. Porcelain Anemone Crabs live together in pairs under the protection of an anemone. It may attempt to defend its territory from clownfish that try to establish themselves among the anemone, although the clownfish generally prevails. It is aggressive toward conspecifics, and should not be kept with larger, aggressive crabs which may attack it.
It eats planktonic food and mucus from the anemone. It may be supplemented with tablet food placed next to the anemone.
It eats planktonic food and mucus from the anemone. It may be supplemented with tablet food placed next to the anemone.
Note by melev: There are two types of Porcelain crabs usually available. The one pictured above, and the purple or green ones that chose to live in the rockwork instead of near an anemone.
PomPom Crab:
A cool looking crab, that may add viewing pleasure to your tank.
Pom Pom Crab, Lybia tessellata, is a curiously comical aquarium addition. This Hawaiian native frequently carries a small anemone in each claw. There are at least two purposes for carrying the anemones. The first is a simple matter of defense. The Pom Pom will taunt would-be predators by shaking the anemones in hopes of stinging the invader into retreat. It also mops the substrate to gather uneaten food, thus creating a symbiotic relationship between the Pom Pom Crab and its pom poms. The anemone undoubtedly benefits by getting to eat its share of the treasure. Also known as the Boxer Crab, it is a hardy creature that grows to about an inch in length. Because of this small size, it is great for the mini-reef aquarium. The Pom Pom Crab is white to tan in coloration and has darker markings covering the body which serve as camouflage for the crab. This crab carries an anemone in each claw which it uses for defense. Besides defense, the crab will also use the anemones to mop up food off of the rocks and substrate. The Pom Pom Crab is an interesting addition to an aquarium with its anemones in each hand. It raises these anemones at would be predators and aids in cleaning the aquarium of any left over food and detritus. Caution should be used when adding this crab to a reef aquarium as the anemones could sting sessile invertebrates and corals. The damage that could potentially be caused by these tiny anemones that come on each claw would be minimal due to their very tiny size.
The diet of the Pom Pom Crab should include meaty foods such as mysis shrimp, chopped fish and clams.
The diet of the Pom Pom Crab should include meaty foods such as mysis shrimp, chopped fish and clams.
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