Coenobita violascens (also known as Viola)is a beautiful but rather uncommon hermit crab in the hobby Coenobita violascens.
Like all hermit crab species, Coenobita violascens has specific requirements for warm temperatures, high humidity, diverse diet, and maintenance.
Although the ecology of this species is poorly researched, in this article, I will tell you everything I know about Violahermit crabs and how to care for them.
|Important: Unfortunately, Coenobita violascens is categorized as a “near-threatened” species by the Japanese Association of Benthology due to habitat loss. These hermit crabs have been protected in Japan since 1970 as a “natural monument” based on the Law for the Protection of Cultural Properties to promote their conservation, meaning that they cannot be collected without permission.|
Quick Notes about Coenobita Violascens
||Sunset Viola, Chocolate Sunset Viola, and Komurasaki land hermit crab|
|Scientific Name||Coenobita variabilis|
|Tank size (minimum)||10 gallons (~40 liters)|
|Average size||2 – 3 inches (5 – 7 cm) in length|
|Optimal Temperature||75 – 86°F (24 – 30°C)|
|Water type||Freshwater and saltwater bowls|
|Substrate||A mixture of cocofiber and sand|
|Life span||up to 10 years|
|Color Form||Brownish-red as juveniles and violescent as adults|
Etymology of Coenobita Violascens
The name “Coenobita” is derived, via Latin, from the Greek words “Koinos (κοινός)”, “common”, and “Bios (βίος)”, meaning “Life”.
The species name “Violascens” is a Latin adjective for “becoming violet”.
Distribution of Coenobita Violascens
This species is majorly distributed in Southeast Asia (Taiwan, India (the Nicobar Islands), Thailand (Phuket), Philippines (the Cebu Island); southwestern Japan (the Ryukyu Islands), and Bangladesh (the northern coast of the Bay of Bengal).
There are some reports that Coenobita violascens has been also found in certain African countries, such as Kenya, Madagascar, Mozambique, Tanzania, Zanzibar, and Mayotte, but it still requires verification and confirmation.
Habitat of Coenobita Violascens
Coenobita violascens is primarily found in the supralittoral zone, mainly in the mangrove estuaries. Juveniles favor the shelter of mangrove forests, while adults venture onto beaches.
Description of Coenobita Violascens
Coenobita violascens is a relatively small hermit crab. Fully grown individuals can grow up to 3 inches (7 cm) or slightly more.
Like most hermit crab species, they do not have complete exoskeletons and use gastropod shells to protect their soft asymmetrical abdomen curved inside empty shells. These hermit crabs use chelae as lids for blocking their shells.
Distinguishing characteristics of Coenobita violascens:
Eyes. They have a compressed ocular peduncle. Their eyes are adorned with black corneas.
Color. Coenobita violascens has different color phases between developmental stages. For example, they are brownish-red as juveniles, appear before sexual maturation, and are violent as adults.
Overall their body color ranges from light lavender to dark violet, with ocular peduncles presenting shades of grayish violet. Light-lavender individuals may showcase an irregular longitudinal patch on the peduncle.
Note: A brownish-red morph was observed in small individuals (2.99–7.22 mm CSL (cephalothoracic shield length)), whereas a violet-colored morph was found in medium to large individuals (7.54–15.73 mm CSL).
Chelipeds. The left cheliped is larger than the right one. It also does not have a stridulating ridge on the upper outer surface of the palm. They have a straight or slightly concave lower margin of palm. Each chela has a tuft of dense setae on the upper inner margin.
Note: Compared with their congeneric nearest neighbor, Coenobita cavipes, Coenobita violascens has a considerably larger body size, shows a higher proportion of individuals protruding from shells, and is unable to pull their left chela into the shell aperture.
Antenna. The antennular peduncles are notably long, with the basal segment sporting a wide, roundish dorsal lobe. The lower part of the flagellum is about half the length of the upper part.
Coxae of males (Fig. 7) are subequal, approximate, both thick and short, each with a dense tuft of setae; no sexual tubes developed; sternal protuberance relatively small.
Telson. The telson has a distinct incision separating anterior and posterior portions. The Terminal margins are unarmed but with long dense setae over the entire length.
For a detailed description of Coenobita violascens, you can refer to this scientific paper.
Lifespan of Coenobita Violascens
Unfortunately, there is no clear information on the maximum lifespan of Coenobita violascens in the wild and captivity.
However, it is assumed that under optimal conditions these hermit crabs can live at least 10 years.
- How long do Hermit Crabs live? Lifespan | Life expectancy
Typical Behavior of Coenobita Violascens
Violas are nocturnal animals. The pick of their activity starts at dusk and gradually stops during the night, before sunrise.
This nocturnal behavior is not uncommon for grazing invertebrates and is mainly associated with attempting to avoid visual predators whilst feeding. However, it does not mean that you will never see them in the daytime. They are simply less active during this time.
Coenobita violascens is very skittish and shy by nature. When hermit crabs feel threatened, their body retracts into the shell whereas their left claw, serving as a shield, closes off the aperture of the shell to protect its body.
They also tend to burry for a long time (even without molding).
They are very social animals. In their natural environment, they interact with each other, forming large colonies that also help them to exchange shells according to their needs.
Coenobita violascens can chirp a lot to communicate or when they feel intimidated.
- Communal: Yes
- Activity: Moderate
- Peaceful: Yes
- Burrowers: Yes
Diet of Coenobita Violascens
These hermit crabs are omnivorous and great scavengers. It means that they will eat practically anything.
In the wild, they generally feed on plant and animal material washed into intertidal and supratidal areas (such as dead animals, feces, leaves, fruits of mangroves, coconuts, and other plants).
Like with other Coenobitu species, they also have a negative preference induction. In other words, they prefer foods that they have not recently eaten.
The food provided should be approximately 20-30% meat-based diets and 70-80% vegetables.
|Hermit crabs 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 violascens will consume foods like:
- carrots (these supply the carotene also needed to maintain their color),
- leafy vegetables,
- oak leaves,
- tree barks,
- nuts and seeds,
- sweet potatoes,
- red peppers,
- dead snails, crickets, (and other insects).
How Often to Feed Coenobita Violascens
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).
Note: Make sure that whatever they do not consume in one day is removed to prevent moles.
- It is very important to not let them starve or deprive them of any food, there is a risk that they can try to go after their tank mates (cannibalize).
Keeping and Housing Coenobita Violascens
To put it in a nutshell, we need to emulate their natural environment meaning: average humidity, high temperature, and some hiding places.
Here are some handy tips that you should follow to keep them happy and healthy.
|Important: The quality of the crabitat is the main factor why our pets have a reduced lifespan (stress, pathogens, and injuries). Unfortunately, a significant number of people make impulsive buys without conducting any prior research.|
Tank Size (Enclosure):
Even though they may be small, these crabs are pretty active at night and need a lot of space to move in the tank.
A 10-gallon (40 liters) tank is recommended minimum for one small Coenobita violascens. For a pair of crabs, you will need a 20-gallon (80 liters) tank or even more.
Having a smaller tank will significantly limit their freedom. As a result, it will stress and make them more aggressive toward each other.
In their natural habitat, these crabs are usually found near the seashore. Therefore, in captivity, they need constant access to seawater and freshwater to maintain gill moisture.
|Important: Coenobita violascens will die without access to fresh and seawater.|
Note: Hermit crabs have a very low resistance to water loss. So, they fill their shell with sea and fresh water inside of the shell for both ionic and temperature balance.
In the crabitat, the presence of both freshwater and saltwater is crucial to creating a favorable environment for this species.
|Provide them with:
You do not have to make huge pools.
Generally, the water only needs to be a few inches deep to completely submerge your hermit crab with a safe way to exit (for example, pebbles, a plastic mesh, etc.).
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. Follow the manufacturer’s instructions to avoid mistakes.
Important: Do not ever use simple aquarium salt or table salt!
How to prepare freshwater:
Provide them with 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 which is toxic to hermit crabs. In addition, chlorine slowly destroys the shell structure.
Instead of waiting for 24 hours, you can also use a water conditioner. For example, Seachem Prime will remove toxic gases and bind to heavy metals, any ammonia, nitrites, or nitrates present for up to 48 hours.
Coenobita violascens prefers a warm temperature range of 75 – 86°F (24 – 30°C). Under lower temperatures, these hermit crabs become sluggish and slow.
Note: Hermit crabs are cold-blooded animals. Their body temperature varies with the temperature of the environment.
If needed, use a quality tank heater or clamp lamp to maintain temperature.
In addition, I also definitely recommend a thermostat. It will protect your hermit crabs from overheating or getting too cold.
|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, partially above the substrate line to heat the air as well.
Hermit crabs need humid air to breathe properly. Thus, an ideal range is considered to be between 70 and 90 %.
Hermit crabs are primarily nocturnal animals. So, there are no special requirements.
Ensure the output is moderate to avoid overheating the tank and harming your hermits.
This is a burrowing species. They burrow to hide, rest, and protect themselves when they are molting.
Therefore, it is absolutely important to have a deep moist substrate into which they can easily burrow.
|The substrate should be at least 6 – 8 inches (15 – 20 cm) deep. If your setup allows it will be better to go even for the deeper substrate.|
The moist substrate has two functions:
- Maintains humidity level.
- Allows hermit crabs to dig underground and form a cave without collapsing.
The substrate should hold its shape when you squeeze it (so-called “sandcastle consistency”). However, not so wet that it drips or pools water.
|Important: Make sure not to waterlog the substrate to avoid the buildup of mold and other parasites.|
Tip: There is a simple trick to test the consistency. Take a pencil 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 regularly to keep it moist enough since the moisture in it will evaporate over time.
Some popular choices of the substrate include:
- coco fiber (Eco earth),
- peat moss,
- organic topsoil,
- Jungle mix soil,
- Zoo Meds Creatures Creature soil,
- The Bio Dude Terra.
It is also possible to use a combination of different substrates, for example:
- sand and coco fiber (5:1 ratio). It is easy to maintain and it holds moisture very well.
- a mixture of peat moss and organic topsoil (1:1 ratio).
|Do not use only sand! Sand often becomes supersaturated even though the top couple of inches are completely dry. If you decide to use sand, do it only in combination with other substrates.|
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!
Coenobita violascens enjoy hiding, burrowing, and climbing.
Therefore, we need to provide plenty of dark hiding spots and other decorations to enrich their environment.
For example, they will appreciate 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.
Shell preference (Shell shop):
Hermit crabs require gastropod shells for their survival. Limited availability of shells will definitely lead to hermit crabs competing and fighting for them.
Of course, we don’t want that.
To avoid (or at least reduce) potential confrontations, provide them with shells of different sizes and shapes.
Many studies and experiments have shown that different species of hermit crabs tend to occupy specific categories of shells about shell species, shape, and aperture shape.
According to the study, the three most common occupied shell species were:
- Chicoreus brunneus(21.3% of hermits),
- Filifusus filamentosus (14.9%),
- Laevistrombus canarium (14.9%).
Biconical shells and those with ovate apertures were the most commonly occupied shell types.
Note: Some other studies also mentioned that Turbo snail shells can be also a good choice for Coenobita violascens.
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.|
Do not forget to keep the crabitat clean. 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 Violascens
- Hermit crabs are not pets you can play with. Do not choose them as pets if you do not like this rule.
- Do not take them out just because you want to. You should really handle them 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 them as well.
Main Care Rules of Coenobita Violascens :
- Keep the environment humid consistently. The humidity levels should be regulated to 70 – 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 highly social.
- Provide various food items to diversify their diet.
- Remove leftovers daily to avoid mold growth.
- Provide deep substrate.
- 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 Violascens and Molting Cycle
Periodic molting is vital for the growth of all hermit crabs. This process is characterized by a complete replacement of the old mineralized exoskeleton with a new one.
In nature, hermit crabs usually shed their old shell and harden their new ones within the burrow to increase their chances of surviving the vulnerable soft-shell stage. Recently molted hermit crabs are soft and may desiccate very fast.
Molting hermit crabs should be disturbed only in emergencies.
Breeding Coenobita Violascens
Unfortunately, it is close to impossible to breed them in captivity. Very little is known about the reproductive biology of Coenobita violascens, an important parameter for understanding the population dynamics of the species.
Currently, the pet industry completely depends on wild-caught species.
So far, there are only a few successfully reared larvae of this species from hatchlings to juvenile crabs under laboratory conditions.
In home conditions, Coenobita violascens was first successfully bred in 2012 by enthusiasts in Germany (Curlz (Melanie)). This is quite an accomplishment!
- Coenobita violascens migrate to the ocean to release eggs that hatch into planktonic marine larvae.
- Males are generally larger than females.
- According to the study, the release of larvae is synchronized with lunar and tidal phases (Nakasone, 2001) as in other decapod crustaceans.
- Females immersed themselves fully or partially in river water and released the hatching zoea larvae.
- Each female may produce thousands of eggs, however, only a small fraction of them eventually metamorphose and crawl back onto land.
- There are 4 larval stages over 15-19 days to reach the megalopae stage.
- It was also recorded that the larvae could not survive to the megalopal stage at temperatures below 68°F (20 °C). The survival rates to the megalopal stage were high at 77 – 88°F (25–31°C) and tended to decline over 90°F (32°C).
- The megalopae immigrate to the coastal area, after which they carry gastropod shells (shell length 4.6–4.8 mm) and migrate onto land.
- Larvae feed on zooplankton, the rotifer species complex, and Artemia sp.
Having Coenobita violascens as pets can be exciting but it is one big responsibility. After all, they can live for several years.
They are easy to care for once you understand their needs and preferences.
These little hermit crabs are cute, unique, and simply amazing! They are very interesting to watch!
- Doi, Wataru, Akira Mizutani, and Hiroyoshi Kohno. “Larval release and associated tree-climbing behavior of the land hermit crab Coenobita violascens (Anomura: Coenobitidae).” Journal of Crustacean Biology 36, no. 3 (2016): 279-286.
- Fujikawa, Shunsuke, Katsuyuki Hamasaki, Shigeki Dan, and Shuichi Kitada. “Emigration behaviour, moulting and survival during the sea-to-land transition of land hermit crabs Coenobita violascens and Coenobitarugosus under laboratory conditions: Effects of salinity and riverine odours.” Biogeography 20 (2018): 111-121.
- Bundhitwongrut, Thanakhom. “Shell occupation by the land hermit crab Coenobita violascens (Anomura, Coenobitidae) from Phuket Island, Thailand.” Nauplius 26 (2018).
- Dugdale, Hannah. “Estate Agency Recommendations for Coenobita violascens .”
- Bundhitwongrut, Thanakhom. “ONTOGENETIC COLOR CHANGE AND SIZE VARIATION OF THE LAND HERMIT CRAB COENOBITA VIOLASCENS HELLER, 1862 (ANOMURA, COENOBITIDAE).”
- Fujikawa, Shunsuke, Katsuyuki Hamasaki, Shigeki Dan, and Shuichi Kitada. “Settlement behaviour of the early megalopae of the land hermit crab Coenobita violascens (Decapoda: Coenobitidae) under laboratory conditions: Effects of inshore odours and salinity.” Biogeography 20 (2018): 21-23.
- Sanda, Tetsuya, Katsuyuki Hamasaki, Shigeki Dan, and Shuichi Kitada. “Low-temperature tolerance of early juveniles of six terrestrial hermit crab species.” Animal Biology69, no. 3 (2019): 349-364.
- 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.
- McLaughlin, P. A., and P. C. Dworschak. “Reappraisal of hermit crab species (Crustacea: Anomura: Paguridea) reported by Camill Heller in 1861, 1862 and 1865.” Annalen des Naturhistorischen Museums in Wien. Serie B fürBotanik und Zoologie(2001): 135-176.
- Photo credit to Ria Tan