Coenobita purpureus, commonly known as Blueberry hermit crabs, is one the rarest pet hermit crab species in the hobby nowadays. This species has been listed as “near threatened” on the Red List by the Ministry of the Environment of Japan.
So, if you by chance buy adopt one you will be surprised to find out how little is known about this species.
In captivity, their habitat should be representative of their natural habitat and their diet should be diverse with provided daily care. As long as you are ready to provide fresh and clean water sources, Coenobita purpureus can be a great companion even for the first-time hermit crab owner.
In this article, I have gathered all information about Blueberry hermit crabs. It covers all aspects, from natural habitat conditions and how Coenobita purpureus should be cared for in captivity, to dietary requirements and behavior aspects.
| Warning: Unfortunately, due to the overharvesting for the pet trade throughout its whole habitat range, Coenobita purpureus has been a Natural Monument Animal since 1970 in Japan.
All Coenobita crabs in Japan are protected from export. You can only keep them if you live in Japan. |
Quick Notes about Coenobita Purpureus
| Name | Blueberry hermit crab |
| Other Names |
Japanese Blueberry hermit crabs, Okinawan blueberry hermit crab, Purple land hermit crab, or Ryukyuan Blueberry |
| Scientific Name | Coenobita purpureus |
| Type | Terrestrial |
| Tank size (recommended) | 10 gallons (~40 liters) |
| Keeping | Easy-moderate |
| Breeding | Very Difficult |
| Average size (total length) | up to 3 – 4 inches (7 – 10 cm) |
| Optimal Temperature | 75–82°F (24–28°C) |
| Water type | Freshwater and saltwater bowls |
| Humidity | >80 % |
| Substrate | Mixture of cocofiber and sand |
| Diet | Detritivore /omnivore |
| Temperament | Peaceful. Social |
| Life span | 4 – 5 years (in captivity) |
| Color Form | From dark blue to light purple |
Distribution of Coenobita Purpureus
Coenobita purpureus is endemic to Japan (the northwestern Pacific region mainly > 24°N). It has a very narrow distribution compared to other Coenobitid hermit crabs are primarily subtropical and tropical species.
In Japan, Coenobita purpureus can be found in the Ogasawara Islands, the Kii Peninsula, southern Kyushu, Miyazaki, Kagoshima, Shirahama, Izu Oshima, and the Okinawa Islands.
Although the Blueberry hermit crab was once recorded on Dongji Island in Taiwan, it is believed that it was caused by a typhoon.
Note: Scientists hypothesize that Coenobita purpureus evolved in the isolated landmasses of the Ryukyu region during the Pliocene (5 to 2.5 million years ago) and that its population expanded and colonized the Ogasawara Islands in the late Pleistocene (2.580.000 to 11.700 years ago).
Natuarl Habitat of Coenobita Purpureus
Small individuals of Coenobita purpureus are generally found at the shore, but the larger ones are less common there. Adults prefer to live further from the shore (up to 650 yd (600 m) or slightly more inland).
Description of Coenobita Purpureus
Coenobita purpureus is a relatively small species. Large individuals can barely reach 2 inches long (5 cm). On average, they are about 1.2 – 1.5 inches (3 – 4 cm) in shield length and up to 3 – 4 inches (7 – 10 cm) in total length.
Like most hermit crabs species, Coenobita purpureus does not have complete exoskeletons and uses gastropod shells to protect its soft abdomen. These hermit crabs use chelae as lids for blocking their shells.
Distinguishing characteristics of Coenobita purpureus:
- Its shield is noticeably narrower anteriorly and swollen just behind the Dorsal surface and posterior and lateral portions with numerous scattered granules on the anterior region. The lateral margins of the shield have setae.
- Eyestalks are rectangular and columnar. There is a white or light yellow ring around the eyes. There are black spots under the eyes. Pale spots are generally absent.
- Coloration usually ranges from dark blue to light However, small hermit crabs are generally of cream color.
- The first pair of front antennae is red and the bottom is white.
- The second pair of front antennae are brown and the bottom is white.
- The antennal acicle fused with the second segment of its peduncle.
- The palm of the left cheliped is larger than that of the right cheliped with a series of 4 or 5 erect ridges on the upper part of the outer surface.
- The upper portion of both palms has numerous scattered granules. The lower portion has a few granules and is nearly smooth.
- There are yellow-brown or purple-red marks near the dactyl and the fixed finger of the left cheliped.
- The outer surface of the propodus of the 3rd walking leg is slightly swollen in middle.
- There are yellow to brownish marks on the joints of the walking legs.
Coenobita Purpureus and Look-Alikes
Color has never been a good way of determining species. Depending on age, natural environment, and diet, coloration may vary within many species.
For example, in early scholarly publications, Coenobita purpureus was initially treated as the synonym of Coenobita perlatus or at least as its variety. From 1890 to 1982, Coenobita purpureus was considered to be the synonym of Coenobita rugosus.
Note: Coenobita Rugosus can also be purple or cream blue. Thus, it is not surprising that Coenobita purpureus can be mistaken for Coenobita Rugosus to the untrained eye. Adult Coenobita brevimanus is also purple in life.
In 2006, a new hermit crab species was found in Indonesia and (in 2016) added to the genus Coenobita. Coenobita Lila has similar colors as the Coenobita Purpureus.
However, Coenobita Purpureus can be separated from Coenobita Lila by the presence of an oblique series of stridulatory mechanisms on the upper outer surface of the palm of the left cheliped, and an asymmetrical sexual tube, with the right one being more slender and longer than the left.
According to Tony, Coenobita Lila also does not have ridges (///) on the big claw.
| In many cases, other hermit species that look alike are sold or given under the name Coenobita purpureus. Thus, do your research. |
Lifespan of Coenobita Purpureus
Currently, there is no available data on the longevity of wild individuals.
Presumably, Coenobita purpureus may live 8-10 years under optimal conditions. However, the average lifespan is around 4 years in captivity.
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Typical Behavior of Coenobita Purpureus
Even though Coenobita purpureus is a naturally nocturnal terrestrial hermit crab, in contrast to other hermit crabs species, they are also diurnally active.
They are also very social. Blueberry hermit crabs do not mind the company of their own kind. However, compared to other species, it looks like they show more dominance toward other hermit crabs.
Coenobita purpureus can be noisy from time to time. According to the study, they produce sound by the friction of the uropods on the inside of the shell when the pleon is moved rapidly back and forth. A sound consists of 1-20 short tones at the highest frequency is 6-8 kHz.
Note: Since males and females are equally capable of producing sounds, it is considered unlikely that the sounds serve to attract the opposite sex.
Coenobita purpureus is a burrowing species. In the wild, they generally, burrow to protect against predators and dehydration by its shell. They are capable of burrowing under debris, between roots and stones, or in damp sand.
Features:
- Social: Yes
- Active: Yes
- Peaceful: Yes
- Burrowers: Yes
Diet of Coenobita Purpureus
The diet of Coenobita purpureus is not well studied. Unfortunately, there are no studies regarding their preferences yet. In the wild, this species was simply observed feeding on dead fish, plants, and half-withered flowers (such as Hibiscus tilaceus).
Based on this, we may safely assume that Coenobita purpureus is feeding generalists and scavengers. As seed dispersers and debris scavengers, they play a very important role by accelerating the decomposition of organic substances.
General recommendations:
The food provided should be with the proportion of approximately 20% meat-based diets and 80% vegetables.
Although most hermit crabs species have seemingly unselective food choices, they may still express food preferences on an individual level. In addition, their behavior generally shows a tendency to avoid food that they had recently eaten. That is why it is highly recommended to change their diet regularly.
| They also require nutrients like calcium, astaxanthin, carotene, and even antioxidants, to be healthy.
Important: Avoid or be very careful with spicy, sour, fatty, salty, sweets, and food from the table. For example, foods high in oxalic acid also impede the absorption of calcium by binding the mineral. |
In captivity, Coenobita purpureus will readily consume foods like:
- corns,
- carrots (these supply the carotene also needed to maintain their color),
- leafy vegetables,
- oak leaves,
- spinach,
- tree barks,
- nuts and seeds,
- bananas,
- cranberries
- broccoli,
- sweet potatoes,
- red peppers,
- pumpkin,
- squash, etc.
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How Often to Feed Coenobita Purpureus
Adults can be fed 3 – 4 times a week whereas juveniles should be fed daily.
- Leave their food in there for 24 hours before removing it (including fruits and vegetables). Just make sure that whatever they do not consume in one day is removed to prevent moles.
- Coenobita purpureus can be pretty aggressive eaters. Thus, do not let them starve.
Keeping and Housing Coenobita Purpureus
The quality of crabitat is the main reason why hermit crabs have a reduced lifespan. Stress and injuries will significantly reduce their survival rate.
It is crucial to understand that to keep them healthy and happy, we have to mimic their natural habitat.
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Tank Size (Enclosure):
Despite their small size, Coenobita purpureus requires a lot of space to move in the tank. They are pretty active in the daytime and very active at night.
A 10-gallon (40 liters) tank is recommended minimum for one small hermit crab.
As I usually say in my guides, having a larger tank is always preferable because it can be easier to make diverse areas for them to hide.
Do not place the tank in direct sunlight, near windows of drafts, or in any place with extreme temperatures.
Important: Having a smaller tank will significantly limit their freedom. It will also make them more aggressive toward each other. Eventually, it will stress them and reduce their lifespan.
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Water:
Compared to other arthropods hermit crabs have a relatively low resistance to high-temperature stress and water loss.
As a result, these animals had to adapt physiological and behavioral (such as large daily migrations, complicated breeding and larvae release behaviors,changes in respiration, circulatory systems, and in the dynamics of molting and food digestion.
In their natural habitat, Coenobita purpureus fill its shell with sea and fresh water inside of
the shell for both ionic and temperature balance
In captivity, the presence of both freshwater and saltwater is absolutely necessary to create a favorable environment for this species.
Provide them with:
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Generally, the water only needs to be a few inches deep to completely submerge your Blueberry hermit crab with a safe way to exit (for example, pebbles, a plastic mesh, etc.). There is no need to make huge pools! In the wild, they rarely make contact with the water, except to lay their eggs.
How to prepare saltwater:
To prepare saltwater you can use Instant ocean marine salt (or similar products – check the price on Amazon). This is a great choice. It is pretty cheap and will last a very long time.
Important: Do not ever use simple aquarium salt or table salt!
How to prepare freshwater:
Ideally, we need to give Coenobita purpureus something like bottled spring water.
Note: Distilled water is not the best option due to a lack of minerals in it.
If you decide to use tap water, let it age for 24 hours before using it. Tap water contains chlorine and it is toxic to them.
You can also use a water conditioner. For example, Seachem Prime will remove also toxic gases, and bind to heavy metals, any ammonia, nitrites, or nitrates present for up to 48 hours.
Important:
- Substances like chlorine, chloramine, and contaminants should be removed from the water before adding it to the tank!
- Do water changes every 2 – 3 days.
Temperature:
The temperature inside the enclosure should always be between 75 – 82°F (24–28°C). Use a quality tank heater or clamp lamp to maintain temperature.
I also definitely recommend a thermostat. It will protect your Coenobita purpureus from overheating or getting too cold.
Remember, these crabs are cold-blooded animals. Their body temperature varies with the temperature of the environment.
Note: According to the study, under constant low-temperature conditions, adult crabs of Coenobita purpureus exhibited higher low-temperature tolerances than Coenobita rugosus.
At the same time, adult Coenobita purpureus were less tolerant to low temperatures compared with juveniles because they died after exposure for 8 days, but juveniles survived for the same period in our laboratory experiments. A temperature level of 46.4°F (8°C) is the low-temperature tolerance limit of juveniles of Coenobita purpureus
Important: It does not mean that the temperature in your crabitat can fluctuate that much in short periods of time! The range of their tolerance is strongly influenced by acclimation temperature. In other words, hermit crabs that are acclimated at lower temperatures can extend their lower temperature tolerance further compared to hermit crabs acclimated to higher temperatures.
| Warning: Heaters should never be placed under the crabitat because they can overheat your substrate and burn or kill molting hermit crabs there. |
The best (safest) option will be to put the heater to the side of the tank, ideally, above the substrate line to heat the air as well.
Humidity:
Humidity levels are really important. Although Coenobita purpureus live on land, these hermit crabs require humid air to breathe properly.
It is recommended to have a humidity level of more than 70%. In ideal range is considered to be between 80 and 90 %.
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Substrate:
As I have already mentioned, Coenobita purpureus are natural diggers. So, you must provide enough deep moist substrate to simulate a natural behavior.
Hermit crabs burrow to hide, rest, and protect themselves when it is molting. It stresses them a lot if they cannot do that.
| The general rule of thumb is that the substrate needs to be 4 – 6 inches (10 – 15 cm) deep minimum or at least twice as deep as your largest crab. If your setup allows it will be better to go even for the deeper substrate. |
To dig underground and form a cave, the substrate should always be kept moist enough. It means that it should hold its shape when you squeeze it (so-called “sandcastle consistency”). However, not so wet that it drips or pools water. Make sure not to waterlog the substrate to avoid the buildup of mold and other parasites.
To get “sandcastle consistency”, a mixture of cocofiber and sand will be the best option.
Many hobbyists use a combination of sand and coco fiber (1:5 ratio). It is easy to maintain and it holds moisture very well.
Tip: There is a simple trick to test the consistency. Take a pencil and stick it down and pull it back up. If the tunnel doesn’t collapse, your substrate is good enough.
The substrate may also require maintenance such as spraying with fresh dechlorinated water on a regular basis to keep it moist enough since the moisture in it will evaporate over time.
Sand options:
- Playsand (It holds its shape very well when made sandcastle consistency).
- Pool Filter Sand (the same as playsand but has a uniform size).
- All-purpose sand (larger grain size compared to playsand and stay moist a little bit better).
How to Prepare Sand
- Place it into a bucket and spray the sand with a hose.
- The excess water will run out of the bucket and the water will be cloudy and dirty initially.
- Keep rinsing. You will notice that the water will run clearer.
- If you think that sand is clean enough – rinse it again for a few more minutes!
Important:
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Lighting:
There are no special requirements. Blueberry hermit crabs are nocturnal animals.
Just ensure the output is moderate to avoid overheating the tank and harming your hermit crabs.
Decorations:
Make sure that your Coenobita purpureus have lots of hiding places. They do enjoy hiding, burrowing, and climbing.
You can use all types of leaves, wood, plants, PVC pipes, alder cones, and other decorations to enrich their environment.
Important: Make sure that the décor is safe as well. For example, avoid using rocks, ceramics, etc. because hermit crabs can damage themselves if they fall.
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Shell preference (Shell shop):
In the hermit crab world, shells are extremely valuable and important. Shells protect them from mechanical damage and desiccation. Given the scarcity of shells, they often fight for them.
Like all hermit crab species, Coenobita purpureus also show a preference for shells with round openings, and/or D-shaped openings.
For example, it was noticed that large hermit crabs often occupied shells derived from the land snail Achatina fulica while smaller ones used shells from the marine snail Lunella granulata.
Some other options include:
- Turbo argyrostomus,
- Turbo setosus,
- Turbo sparverius,
- Turbo tumidulus,
- Turbo petholatus,
- Pugilina cochlidium,
- Pugilina tuba,
- Bufonaria echinata,
- Bufonaria crumena,
- Bufonaria elegans,
- Bufonaria margaritula, etc.
The crabs’ left chelae, which are larger than their right chelae, serve as lids for blocking their shells. In addition, in the wild, Coenobita purpureus with suitable and relatively intact shells tend to move further inland.
Warning: Do not use glass shells. First, these shells are very heavy for hermit crabs. Second, they do not provide enough secrecy. In transparent shells, they cannot hide and it stresses them out even more.
| Important: provide them with lots of shells to choose from. The “Shell shop” should contain shells of different shapes and sizes. It is recommended to have at least 5 shells per hermit crab, but more is always better. |
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Cleaning:
Keeping crabitat’s cleanliness is important. Remove their feces and food crumbs as often as you can. It will increase their survival rate.
Direct and prolonged contact with its waste and leftovers may lead to dangerous pathogenic agents infecting the organism.
Handling and Bathing Coenobita Purpureus
You need to handle your hermit crabs with utmost care. They are not pets you can play with.
Do not take them out just because you want to. You should really handle him as little as possible. They stress very easily.
Be cautious too, they can snap at your fingers with their pincers. Generally, it does not hurt BUT you can flick your hand instinctively and your pet will go flying somewhere. They can get hurt easily, even with their hard shells.
Despite popular practice, it is not recommended to bathe Coenobita purpureus as well.
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Main Care Rules of Coenobita Purpureus:
- Keep the environment humid consistently. The humidity levels should be regulated to 80 – 90 %, monitor this with a humidity gauge or hygrometer.
- The substrate should be kept damp (‘sandcastle consistency’). Check it daily.
- Provide as many décors as you can!
- Eliminate chlorine and contaminants from the freshwater before usage.
- Replace the water at least once every 2 – 3 days.
- Clean their water bowls and enclosure.
- Don’t keep only one crab. They are social.
- Provide various food items to diversify their diet.
- Remove leftovers daily to avoid mold growth.
- Replace the substrate bedding at least once every 6 – 8 weeks with a fresh one.
- Hermit crabs’ health needs to be maintained by separating them from specks of dirt, such as food and metabolic waste (feces and urine).
- Make sure the lid of the tank is closed tightly so that they cannot escape it.
- When they are under the substrate, do not dig them up unless you absolutely have to!
Coenobita Purpureus and Molting Cycle
In order to grow, Coenobita purpureus will shed its exoskeleton in a process called molting. It also allows them to restore lost limbs.
In nature, hermit crab usually sheds its old shell and hardens its new one within the burrow to increase its chances of surviving the vulnerable soft-shell stage. Recently molted hermit crabs are soft and also may desiccate very fast.
Molting hermit crabs should be disturbed only in emergency situations.
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Breeding Coenobita Purpureus
Unfortunately, breeding Coenobita purpureus is extremely difficult in captivity. So far, there are only a few documented successful attempts to breed them.
Sexing:
Coenobita purpureus is characterized by sexual dimorphism.
In males, coxae of the 5th legs of both sides are produced ventrally, unequal coxa, and the right side is produced into an elongate tube, generally longer than the left one; the right tube is turned towards the left and curved ventrally.
According to the study, the size (carapace length) of the smallest ovigerous female was 3.83 mm. Some females may lay eggs during their second year of
life.
The smallest males in which spermatophores were present in dissected vas deferens were 4.94 mm for Coenobita purpureus.
In the natural habitat, the breeding season lasts from late May to mid-September.
Eggs:
Females retain eggs throughout their entire development. Presumably, the eggs are fertilized by means of the spermatophore soon after being laid.
Females carry the eggs for about a month. They are hidden in the shell.
Hatching:
After hatching, coenobitid larvae spend their pelagic life through the zoeal stages to megalopae for several weeks in the sea.
The complete larval development of Coenobita purpureus is described and illustrated based on larvae reared in the laboratory.
Coenobita purpureus has 5 zoeal (larvae) stages. The zoea-egg hatches out almost immediately at a stimulus exerted by seawater, and the zoea becomes free. It generally swims in a heads-down position.
| # | Average total length (mm) | Duration (days) |
| Stage 1 | 2.70 | 6 |
| Stage 2 | 3.27 | 4 |
| Stage 3 | 4.20 | 5 |
| Stage 4 | 4.57 | 2 |
| Stage 5 | 5.15 | 10 |
| Megalopal stage (glaucothoes) |
4.28 | 5 |
After settling, megalopae acquire empty gastropod shells and emigrate from the sea to land where they bury themselves in the sand before metamorphosis. After that, they emerge as the first crab stage.
Note: Depending on the temperature (for example at 82°F or 28°C), the megalopae metamorphose into the first crab stage 5–6 days after landing.
Some additional information:
- Experiments showed that Coenobita purpureus can tolerate high salinity conditions from 35 ppt to 40 ppt salinity conditions. However, the survival rate at 40 ppt was less than 70%.
- Larvae cannot survive at temperatures below 67°F (19°С). Eventually, they have molting problems and die.
- They should be fed newly-hatched Artemia nauplii.
- The survival rate also drops significantly due to the predation of 5th zoeae by glaucothoes and the cannibalism of glaucothoes.
Coenobita Purpureus and Suitable Tankmates
The lack of social need stresses Coenobita purpureus and shortens their lifespan. Ideally, they should be kept with conspecifics, since it’s unclear if the critter can live peacefully with other terrestrial animals like geckos, lizards, salamanders, newts, etc.
These hermit crabs can be a little bit aggressive during feeding but, generally, they do not fight very often. However, newly molted hermit crabs can be attacked by others (they are attracted by the smell).
To prevent them from fighting, you can dip them both in the water bowl so they will smell the same. If it does not help, you need to isolate them for a few days.
In Conclusion
As a hermit crab owner, you should always be monitoring the health of your pet and watching out for any indicators of concern because the absolute majority of issues can be traced back to poor care in feeding patterns, inadequate water, and tank maintenance.
Coenobita purpureus can be extraordinary companions for many years! However, it also means that you should only acquire these animals if you are willing to give them the special care and attention they need.
References:
- Sanda, Tetsuya, Katsuyuki Hamasaki, Shigeki Dan, and Shuichi Kitada. “Expansion of the northern geographical distribution of land hermit crab populations: colonization and overwintering success of Coenobita purpureus on the coast of the Boso Peninsula, Japan.” Zoological studies 58 (2019).
- Hsu, Chia-Hsuan, and Keryea Soong. “Has the land hermit crab Coenobita purpureus settled in Taiwan?.” Crustaceana 90, no. 1 (2017): 111-118.
- Gusev, Oleg, Tracy A. Ziegler, and Masayuki Saigusa. “Expression and structure of stress chaperon hsp90 in terrestrial decapods, Coenobita (Anomura: Coenobitidae) and Chiromantes (Brachyura: Sesarmidae).” Crustacean Research 6 (2006): 109-119.
- Nakasone, Yukio. “Larval stages of Coenobita purpureus Stimpson and C. cavipes Stimpson reared in the laboratory and survival rates and growth factors of three land hermit crab larvae (Crustacea: Anomura).” Zoological science 5, no. 5 (1988): 1105-1120.
- Nakasone, Yukio. “Reproductive biology of three land hermit crabs (Decapoda: Anomura: Coenobitidae) in Okinawa, Japan.” Pacific Science 55, no. 2 (2001): 157-169.
- Hsu, Chia-Hsuan, Yi-Bei Liang, Jheng-Jhang Li, and Chi-Chang Liu. “Ecological information of land hermit crabs (Crustacea: Decapoda: Anomura: Coenobitidae) and new record in Dongsha Atoll National Park, Taiwan.” Taiwania64, no. 3 (2019): 299-306.
- Imafuku, M. (2002) Ecology of the Land Hermit Crab Coenobita purpureus on Kikajima Island. II Breeding behaviour, Food, Predator, Orientation and the Environment. Mem. Fac. Sci. Kyoto Univ (Soc. Biol.), 18: 15-34. Dec 2002
- Hamasaki, Katsuyuki. “Effect of temperature on larval survival, development and duration of six terrestrial hermit crab species under laboratory conditions.” Aquatic Animals (2020): AA2020-6.
- https://coenobitaspecies.com/coenobitidae-family/
- https://tonycoenobita.com/coenobita_rugosus_eng.htm
- http://decapoda.free.fr/illustration.php?n=6&sp=187
- https://hermitcrabassociation.com/