smallest crab species

The Blue Leg Hermit Crab (Clibanarius tricolor) is a small marine invertebrate heavily exploited by the ornamental pet industry. Hermit crabs are unique among higher crustaceans (like shrimp, crabs or crayfish) because they generally utilize snail shells as portable shelters for protection because their body is soft and fragile.

Among hermit crabs, the Blue Legged Hermit Crab is highly valued both because of its aesthetic value and apparent ability to control the small sea anemone Aiptasia spp., considered a nuisance by aquarium hobbyists. In addition to their colorful appearance, they are low maintenance hermit crabs that are very hardy and require little care.

In this article, I discuss everything you need to know about the Blue Leg Hermit Crab including how to care for them, behavior, tank mates and much more.

Quick Notes aboutBlue Leg Hermit Crab

Name	Blue-Legged Hermit Crab
Other Name s	Dwarf Blue Hermit Crab, Equal-Handed Hermit Crab, Blue-leg Reef Hermit Crab
Scientific Name	Clibanarius tricolor
Tank size (minimum)	5 gallons (~20 liters)
Keeping	Easy
Breeding	Very Difficult
Size	up to 2.5 cm (~1 inch)
Optimal Temperature	22 – 26°C (~72°F – 80°F)
Water type	SG = 1.018 – 1.025
Optimal PH	8.0 – 8.5
Optimal KH	8 – 16
Nitrate	Less than 20 ppm
Diet	Omnivore/Carnivore
Temperam ent	Semi-aggressive
Life span	up to 2 years
Color Form	Blue, Black, Orange

Origins, Natural Habitat of the Blue Leg Hermit Crab

The Blue Leg Hermit Crab, scientifically known as "Clibanarius tricolor", is certainly one of the most abundant and widespread small hermit crab species throughout the Caribbean Sea and western Atlantic.

They are very common in shallow waters (in two meters or less), along open shores on both the north and south coast of Curasao.

These hermit crabs form temporarily large aggregations during low tides in the intertidal zone where they find refuge in depressions beneath rocks on hard-bottoms.

Description of the Blue Leg Hermit Crab

Clibanarius tricolor - Blue Leg Hermit Crab There are about 500 known species of the hermit crab, and the Blue Legged Hermit Crab is one of them.

It is a small crab. Large males can barely reach 1 inch long (2.5 cm), and as the name implies, they have blue legs. The blue, orange and yellow-banded ambulatory legs are strikingly colored. As with most species, the walking legs are almost all that an aquarist sees in the tank.

Blue Legged Hermit Crabs have both claws equal, unlike most species of the hermit crab. That's why they are sometimes referred to as the 'Equal-handed hermit crab'. These crabs also have bright orange antennas that make them look even flashier.

This species uses shells from various gastropods but most often Cerithium spp.

On average, Clibanarius tricolor species lives for about 2 years, but under good conditions can live a little longer.

Behavior of the Blue Leg Hermit Crab

According to the experiments, in the wild, Blue Legged Hermit Crabs exhibit high site fidelity and do not make large daily movements, having an average home range no larger than 2 m in diameter.

This species is nocturnal. During the day, the crabs move about slowly or rest. Feeding activity begins at dusk and continues throughout the night.

Blue Leg Hermit Crabs are social and relatively peaceful animals. They usually congregate among detritus-covered rocks as a group.

Interesting fact: Blue Leg Hermit Crabs prefer to stick to their own group. That way they feel more comfortable and secure.

In another experiment, biologists marked the shells of two different groups with red and blue ink and replaced them in their respective groups. However, the observations for the first few days revealed relative group stability. The majority (82%) of the marked Blue Leg Hermit Crabs returned to their own group.

Clibanarius tricolor is neither a rapidly nor slowly moving crab relative to other species. Although surprisingly agile for an organism carrying so much extraneous weight, individuals often tumble over backwards when attempting to crawl over an obstacle and lose their hold on it. They are usually able to right themselves rapidly through movements of their second legs.

Blue Leg Hermit Crabs usually do not show any change in their behavior when they meet. One may crawl over the other or they may pass one another without any apparent notice. Even when of the hermit crabs starts making aggressive movements, the other frequently shows no change in behavior, unless they are attacked.

Blue Leg Hermit Crabs and Shell-fighting Behavior

When two crabs come in contact, the most frequently used aggressive signal is the single raise of the legs (0.24 seconds). The ambulatory raise is executed with the limb held rigid and straight. However, the leg is rarely raised to a completely perpendicular position.

In more intense aggressive interactions, individuals of tricolor may employ all four ambulatory legs in a quadruple raise. While all four legs are engaged in this manner, the animal maintains an upright position by using its claws for support and/or leaning back, balancing itself on its shell.

In hermit crab world, shells are extremely valuable and important. They often fight for them.

An attacking Blue Leg Hermit Crab often moves into contact from behind and turns the other on its back. Next, it starts shaking the other crab until it cannot hold the shell. After an initial investigation, the attacker usually moves into the new shell.

It does this in such a manner that it maintains possession of both shells even after it has moved into the new one. Presumably testing the fitness of the new shell. Once occupied and satisfied with the new shell, the winner releases the old one, therefore, the losing crab moves into the old shell of the winning crab.

Important: It is very important to keep a few additional shells in the aquarium. The point is that in crowded conditions, such as are common in nature for this species, the loser is subject to almost certain death from the attacks of other crabs, fish, etc. If the winner prevents its entering a shell for more than a few seconds. A naked crab cannot protect its abdomen and can be torn to bits rapidly.

Feeding Blue Leg Hermit Crab

These hermit crabs have become popular residents of aquariums because of their so-called "janitorial capabilities."

The Blue Leg Hermit Crabs is an active omnivore in their diet and opportunistic in their feeding habits. They spend most of their time looking for food such as organic debris, decayed and fresh macro-algae, macroscopic pieces of dead and live animal tissues.

In the aquarium, they usually play the role of a clean up crew. The Blue Leg Hermit Crabs will eat fish or shrimp food leftovers, fish wastes, leftover meaty food, dried seaweed, dead plants, many types of macroalgae including green hair algae and cyanobacteria and will sift the substrate for foodstuff. Because of their small size, they will able to reach some areas other tank janitors cannot reach.

Note: I would like to add that some aquarists consider their hermit crabs to be the scavengers and do not even think to feed them any additional food. Well, this is true, they are scavengers. However, I would still advise providing the occasional treat for the hermits. For example, you can give them – krill, Mysis, frozen carnivore cubes, pellets, flakes and they will be very grateful for it.

Blue Leg Hermit Crabs and sea anemone Aiptasia spp.

Blue Leg Hermit Crabs have been reported eating Aiptasia . This is great, isn't it? The problem is that if they can find something else to eat, they will always choose the more tasty food over the Aiptasia. Therefore, in tanks with lots of goodies and excess feeding, these crabs will tend to ignore the Aiptasia.

Is Blue Leg Hermit Crab Reef-Safe?

In most cases, Blue Leg Hermit Crabs are almost completely reef safe. It makes them some of the few good tankmates for the Beadlet Anemone.

However, there are still reports that aquarists had better success in keeping corals alive without Blue Leg Hermit Crabs. They say that some of these crabs kept crawling on and picking their SPS corals . Sharp feet can damage the soft flesh of the corals.

Keeping and Housing Blue Leg Hermit Crab

The Blue Leg Hermit Crabs are very popular due to their small size and ease of care. They can be a great addition to a reef aquarium. It is always important to try and transfer a species natural environment into the tank.

Tank Size

They require a minimum tank size of 10 gallons for a small group of 2 – 3 crabs. Ideally, to avoid crowding the aquarium, one should aim for just one Blue leg hermit crabs per 3 – 4 gallons of water.

Water Parameters

The water in the tank where a Blue leg hermit crab would be residing should be between 22 – 26°C (72 – 80 °F), with a pH value between 8.0 – 8.5. The tank should also have a specific gravity of 1.020 to 1.025, and the hardness of the water should also be between 8-16 °d. They can tolerate most types of water movement but prefer slow-moving water.

In general, they are not very picky creatures. If given time, they can adapt to a higher or lower temperature, salinity, and other water parameters.

Substrate and Decorations

For the substrate, you can use either sand or small gravel. Remember that in the wild, Blue leg hermit crabs usually prefer to live in intertidal sandy-bottom substrates. Therefore, sand is the most ideal substrate for them. These crabs are great at aiding in aerating the substrate as well.

Tip: If you are purchasing gravel, make sure that the grains are small enough for the hermit crab to sift.

Include plenty of live rock for the hermit crab to graze on, and the rock will also double as hiding areas that help to make it feel secure.

Filtration and Lighting

They do not need fancy filtration and lighting. You can just purchase a normal LED aquarium light.

Important: Before putting them in your tank do not forget to acclimate them (read more about it) .

Identifying andSexing Blue Leg Hermit Crab

Overall, males are generally larger than females. Other than general size, there is no visible external sexual dimorphism. Unless your hermit crab is willing to come rather far out of its shell for you.

In this case, the Blue leg hermit crab's sex can be determined according to the presence or absence of external primary sexual traits. The female hermit crab has tiny genital openings called gonopores. The gonopores are located on the fifth pair of pereopods in females and at the base of the third pair of pereopods in males.

Interesting fact: Blue leg hermit crabs have also intersex individuals. However, they do not occur often in Clibanarius tricolor species.

MatingBlue Leg Hermit Crab

As in many crustaceans, Blue leg hermit crabs can successfully mate only for a short time following a female molt.

Biologists do not know how but male hermit crabs can feel when a female will be ready to molt and grasp her prior to her molting. This time may vary from a few minutes to 6 hours. The male may start violent rocking and the frequency of occurrence gradually increases.

Shortly before copulation, the female molts. When the female molts, the male grabs at the old exoskeleton of the female and pulls it out of the shell. By doing so, the male actually "helps" the female out of her exoskeleton by actively pulling at the legs and chelipeds. The copulation lasts only 1-3 seconds.

After copulation, the male may push the female away and mating is completed. However, in most cases, the male Blue leg hermit crab stays with the female and continues to do a series of violent and gentle rocking.

This kind of behavior protects the recently molted and weak female from being attacked by other shell-seeking hermit crabs. During this time, the female's exoskeleton hardens.

Breeding Blue Leg Hermit Crab

It is relatively difficult to breed a Blue Leg Hermit Crab in captivity. I have tried my best but could not find any proof that anybody managed to breed them in their aquariums. Hermit crabs' larvae have differing salinity needs making them almost impossible to captive breed.

Even biologists say that they also know little about reproduction among Clibanarius tricolor species.

They do not even know what type of egg development (e.g., direct, abbreviated, indirect) they have.

The only facts that we know about breeding Blue Leg Hermit Crabs is that:

Fecundity usually increases with female body size in hermit
The egg clutch varied between 200 – 600 embryos crab.

Blue Leg Hermit Crab and Suitable Tankmates

The Blue Leg Hermit Crab can live in peace with other aquatic animals. Although they live in a hard shell, it is advisable to take caution when you intend to keep them with the more aggressive marine invertebrates.

For example, you can keep them with non-aggressive and relatively small fish like Mollies, Guppies, Tetras, Zebra Blennies, etc.

Try not to keep them in the same tanks with snails because they can try to kill them just for their shells. Cerith snails are particularly favored by Clibanarius tricolor, so reef safe does not mean snail safe. Of course, if you provide enough empty shells in your aquarium you will avoid a lot of problems. However, it will not eliminate them. If the Blue Leg Hermit Crab decides that it need this particular shell, it can be hard to dissuade!

Avoid overstocking them. These hermit crabs can become aggressive if there are too many of them in an aquarium due to competition for their shells. and could become destructive if food supply reduces.

Blue Leg Hermit Crab can share the same tank with other hermit crabs like Halloween hermit crabs (Ciliopagurus strigatus) . These species prefer different types of snail shells, so you should not have any problems with that.

Marine shrimp like Skunk Cleaner Shrimp , Red Fire shrimp , Peppermint shrimp , Harlequin shrimp will be also good tank mates for the Blue Leg Hermit Crab. Regarding Coral banded shrimp , I would not recommend putting them together.

In Conclusion

Blue Leg Hermit Crabs are beautiful and eye-catching in color as well as being very easy to take care for. One of the greatest advantages of owning them is that they help in the cleaning of wherever tank they find themselves. It makes them almost ideal creatures for many aquarists.

References:

Social Behavior of the Paguridae and Diogenidae of Curaçao. Front Cover. Brian A. Hazlett. M. Nijhoff, 1966.
Pagurus bernhardus()–an introduction to the natural history of hermit crabs. Ian Lancaster. Field studies. 1988.
Foraging behaviour of the hermit crab Clibanarius erythropus in a Mediterranean shore. Article in Journal of the Marine Biological Association of the UK. June 2003. DOI: 10.1017/S0025315403007331h.
Small-scale spatial variation in population- and individual-level reproductive parameters of the blue-legged hermit crab Clibanarius tricolor. Article in PeerJ5 (e3004). February 2017. DOI: 7717/peerj.3004.
Shell acquisition by hermit crabs: which tactic is more efficient? Elena Tricarico. Francesca Gherardi. Behav Ecol Sociobiol (2006) 60: 492–500 DOI 10.1007/s00265-006-0191-3

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