Despite their small size, Aussie or Crazy crabs (Coenobita variabilis) are highly prized by hobbyists who desire to keep them as pets. Nonetheless, this is a very rare species of hermit crab and is not commonly found in pet stores.
Coenobita variabilis, like many other hermit crab species, requires specific conditions in terms of temperature, humidity, diet, and maintenance to thrive. Based on this, I would say that these hermit crabs are not for beginners.
This comprehensive guide covers everything from its natural habitat to its care requirements, dietary needs, and behavioral characteristics. Ideal for both experienced and new hermit crab hobbyists, it will provide you with the information you need to ensure your Coenobita variabilis thrives in captivity.
|Important: It is illegal to collect these crabs in the wild. To collect and export Coenobita variabilis in Australia, traders need a commercial license and a declaration for an approved wildlife trade operation, which includes a collection quota and duration, from the Department of Fisheries and the Department of Sustainability, Environment, Water, Population, and Communities.
Quick Notes about Coenobita Variabilis
|Australian terrestrial hermit crab, Calico crab, Aussie crab, and Crazy crab
|Tank size (minimum)
|10 gallons (~40 liters)
|1 – 1.5 inches (3 – 4 cm) in length
|78 – 90°F (26 – 32°C)
|Freshwater and saltwater bowls
|Mixture of cocofiber and sand
|up to 10 years
|Pale brown, reddish brown, beige, or cream color
Why are Rhey Called “Crazy crabs”?
Coenobita variabilis, commonly known as “crazy crabs” in Australia, has no correlation with their way of life.
It is believed that the first expedition to collect these hermit crabs was conducted with this motto, and since then, the unusual name has been associated with this species.
Distribution of Coenobita Variabilis
Natuarl Habitat of Coenobita Variabilis
Coenobita variabilis is often found in coastal sand dunes and supratidal regions, especially behind sheltered sandy beaches. Adult individuals are known to inhabit areas up to 110 yards (100 meters) or more offshore, where they can be found in mangrove forests.
During the day, they seek shelter under logs and litter, making these areas ideal habitats for them.
Description of Coenobita Variabilis
Coenobita variabilis is a small terrestrial hermit crab, typically measuring between 1 – 1.5 inches (3 – 4 cm) in length, making it one of the smallest species in the genus Coenobita.
Like other hermit crab species, Coenobita variabilis lacks a complete exoskeleton and instead relies on gastropod shells for the protection of its vulnerable abdomen. These crabs use their chelae to close the opening of the shell, serving as a lid to secure their delicate bodies.
Distinguishing characteristics of Coenobita variabilis:
Coenobita variabilis resembles Coenobita compressus with a compact look.
- Color. Its exoskeleton is usually a pale brown, reddish brown, beige, or cream color, often with darker (brown) spots. The anterior part of the exoskeleton is white. the color is not often homogeneous throughout the exoskeleton. The juvenile form is similar to the adult but whiter.
- Dorsal surface. The head has a brown “M” shape. There are many black granules on the exoskeleton.
- Eyes. The eyes are elongated and are the same color as the exoskeleton.
- Claws. The left claw is more developed and has stripes (////), as well as the second and third pairs of legs.
- Antennae. Antennae are beige.
- Abdomen. The abdomen is short and voluminous.
Lifespan of Coenobita Variabilis
At present, there are no exact data on how long Coenobita variabilis can live in the wild. Nonetheless, according to existing reports on their captivity, some individuals can live an average of 10 years. The estimated maximum for this species is 20 years.
Typical Behavior of Coenobita Variabilis
Coenobita variabilis is most active at night and usually begins its activity shortly before sunset. However, in humid and vegetated areas, or in captivity, they often may remain active even during the day.
These crabs are social animals and in the wild, they form large colonies where they interact and exchange shells with one another. Sure you may see them fighting (pushing and climbing on each other), however, it does not generally cause any damage. Dominance and establishing a pecking order is a pretty usual behavior in hermit crabs’ world.
Aussie crabs are known for their high activity levels. These hermit crabs are known for their quickness and will often flee, sometimes even leaving their shells behind when pursued.
Note: Probably this is another theory why they got called – Crazy crabs. In reality, there is a simple explanation, the shells they carry come with a metabolic cost, which increases with slower walking speeds.
Coenobita variabilis loves to climb and dig. Therefore, a balanced blend of climbing and digging space is necessary for these hermit crabs to thrive.
- Social: Yes
- Active: Yes
- Peaceful: Yes
- Burrowers: Yes
Diet of Coenobita Variabilis
In nature, these hermit crabs are generalist scavengers. It means that they will feed on a variety of plant and animal matter found in intertidal and supratidal areas, such as dead animals, feces, leaves, fruits of mangroves, and other plants.
In terms of their dietary preferences, this species also exhibit a phenomenon known as negative preference induction, where they tend to choose food items that are not part of their normal diet more often than would be expected by chance. This means that they prefer foods they haven’t recently consumed.
The food provided should be approximately 20% meat-based diets and 80% vegetables.
|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 variabilis 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 Variabilis
For adults, it is recommended to feed them 3 to 4 times a week, while juveniles should be fed on a daily basis.
Food Duration: Place their food in the enclosure and allow it to be available for 24 hours before removing it, including fruits and vegetables.
Important Note: Make sure to remove any uneaten food within 24 hours to prevent mold growth.
Eating Habits: Coenobita variabilis are known to be aggressive eaters. It is crucial to not deprive them of food, as this may result in them trying to consume their tank mates (cannibalism).
Keeping and Housing Coenobita Variabilis
Hermit crab lifespan is often shortened due to poor crabitat quality. Inadequate housing can cause stress, expose them to harmful pathogens, and increase the risk of injury, leading to a decrease in their overall survival rate.
Tank Size (Enclosure):
Despite their small size, Aussie hermit crabs are highly active animals and require ample space for movement. A minimum tank size of 10 gallons (40 liters) is recommended for one adult Coenobita variabilis, while a pair of crabs will require at least 20 gallons (80 liters), or even more.
|Important: It’s important to keep in mind that these crabs are known to dig extensively, so having a larger tank offers more room for creating diverse hiding places and reducing stress. A smaller tank will restrict their movements and potentially increase aggression between them.
These hermit crabs adapted to life at (or near) the coast. Thus, they require constant access to seawater in captivity to maintain moisture in their gills. Without access to both fresh and seawater, they will not survive.
In the crabitat, the provision of both freshwater and saltwater is crucial for creating a suitable environment for this species.
Important: It’s important to note that hermit crabs have a low resistance to water loss and need to maintain a balance of both sea and fresh water in their shells for ionic and temperature stability
|Provide them with:
There is no need for large bodies of water.
Typically, a few inches of water is sufficient for fully submerging Coenobita variabilis. Although these hermit crabs can stay underwater for an hour or so, it will be better to provide them with a secure exit route, such as via pebbles or a plastic mesh.
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:
To ensure the well-being of your Coenobita variabilis, it’s best to provide it with bottled spring water. Avoid using distilled water as it lacks the necessary minerals.
Tip: If you have to use tap water, let it sit for 24 hours or treat it with a water conditioner, such as Seachem Prime, to remove toxic elements and heavy metals. This will help protect the shell structure and ensure a safe environment for your hermit crab.
To ensure the well-being of Coenobita variabilis, the temperature inside the enclosure should be kept between 78 – 90°F (26 – 32°C). They love warm temperatures.
Lower temperatures can make the hermit crabs become sluggish and slow, and if it remains low for a sustained period, they may burrow and even enter a semi-hibernation state.
Note: Hermit crabs are cold-blooded animals. Their body temperature varies with the temperature of the environment.
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 require humid air in order to breathe properly, with an ideal humidity level between 70 and 90%.
Aussie hermit crabs are enthusiastic diggers, so providing them with a deep, moist substrate is essential. This should be at least 6-8 inches (15-20 cm) deep, and should be able to hold its shape when squeezed – having a “sandcastle consistency”.
|“Sandcastle consistency” – means that it should not be too dry or wet, as this can cause it to drip or pool water. 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.
This substrate is essential for creating a cave in which the hermit crabs can hide, rest, and protect themselves when they are molting – which is a natural process for them. If they cannot do this, it can cause them a lot of stress.
The moist substrate has two functions:
- Maintains humidity level.
- Allows hermit crabs to dig underground and form a cave without collapsing.
Some popular choices of 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:
- coco fiber and sand and (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!
No specific requirements are necessary for keeping Aussie hermit crabs, as they are nocturnal animals that require only ambient light.
Hiding places (Decorations):
The main goal of decorations in a tank is to replicate their natural habitat, allowing them to hide, burrow, and climb. This will provide them with the shelter and protection they need, particularly if they are kept in a community tank.
To achieve this, choose décor items such as leaves, wood, plants, PVC pipes, cones, and other natural decorations.
|Important: It is important to ensure that they are safe; avoid rocks, ceramics, etc. as they could cause injury if the hermit crabs fall.
Shell preference (Shell shop):
Coenobita variabilis is a species of hermit crab that depends critically on gastropod shells for its survival. Limited availability of shells can lead to hermit crabs competing and fighting for them.
It was observed that these hermit crabs prefer light and “D”-shape shells, such as:
- Turbo sp.,
- Babylonia sp.,
- Tonna sp.,
- Phasianella sp.,
- Murex sp., etc.
Interesting fact: Generally, Coenobita variabilis have a tendency to extensively remodel the exterior and interiors of their shells to make them even lighter and fit them perfectly.
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.
It is essential to maintain the cleanliness of a crabitat by regularly removing feces and food crumbs. This will not only improve the environment for the crab but also increase its chances of survival.
Exposure to environmental contaminants, such as waste and food leftovers, can cause crabs to become infected with pathogens that can lead to severe illness and even death. Therefore, it is important to ensure that the crabitat is regularly cleaned to ensure the crab’s safety and well-being.
Handling Coenobita Variabilis
It is essential that you handle your hermit crabs with extreme caution. Do not take them out of their habitat just for fun. They become very stressed in unfamiliar environments.
Main Care Rules of Coenobita Variabilis:
- Maintain a consistent and regulated humidity level of 70-90%.
- Keep the substrate damp (like sandcastle consistency) and check daily.
- Provide multiple decorations for the enclosure.
- Ensure that the water is free of chlorine and contaminants.
- Replace water in the bowls at least every 2-3 days.
- Regularly clean the water bowls and enclosure.
- Provide a social environment by keeping multiple hermit crabs.
- Offer a varied diet with various food items.
- Provide a deep substrate bedding.
- Replace the substrate bedding every 8 weeks.
- Remove food leftovers daily to prevent mold growth.
- Keep the hermit crab healthy by removing dirt, food waste, and metabolic waste (feces and urine) from the enclosure.
- Secure the lid of the tank to prevent escape.
- Avoid disturbing hermit crabs while they are under the substrate. DO NOT dig them up unless you absolutely have to!
Coenobita Variabilis and Molting Cycle
Molting is a process in which hermit crabs shed their old exoskeleton and form a new, larger one. It is a natural part of their growth and development, allowing them to increase in size and replace damaged or lost appendages.
Hermit crabs typically molt in their burrow.
It’s important to note that freshly molted hermit crabs are delicate and susceptible to drying out, so they should only be handled in emergency situations.
Breeding Coenobita Variabilis
The coenobitid crabs, although terrestrial as adults, have a unique life cycle that starts in the sea. Their eggs hatch into the ocean and the larvae progress through multiple planktonic zoeal stages before reaching the megalopal stage.
After settling, the megalopae find and occupy gastropod shells, then migrate to land where they undergo metamorphosis into their first crab stage.
|Unfortunately, breeding hermit crabs in captivity remains a challenging task. Currently, there are only a few hobbyists who have been successful in doing so in home conditions. One of the reports can be read here.
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.
Male hermit crabs can detect females using their antennules and differentiate between receptive and unreceptive females, suggesting that females regularly release pheromones into the environment.
In Coenobita variabilis, females start to lay eggs when they are around 0.8 inches (2 cm) in size.
The number of eggs that a female hermit crab can carry is currently unknown. However, it is estimated that they can carry several thousand eggs.
During a gestation period of about a month, the eggs are carried in a concealed location within the female’s shell.
According to the study, development in Coenobita variabilis is comprised of two brief, non-feeding zoeal stages followed by a feeding megalopal stage, which only metamorphoses on land.
This is the first recorded instance of abbreviated development in this family.
|Total length (mm)
|5.18 ± 0.09
|2 – 4
|5.3 ± 0.21
|2 – 5
|4.38 ± 0.16
|6 – 7
After non-feeding zoeal stages, they will gladly take Artemia and other fish food (such as spirulina powder, crushed meal worms, and powdered cuttlebone).
Coenobita Variabilis and Suitable Tankmates
Coenobita variabilis has a strong social nature and thrives in large groups in the wild. To ensure their well-being, it is not advisable to keep them isolated. Lack of social interaction can cause stress and shorten their lifespan.
It is best to keep them with other hermit crabs of similar size, as larger species may bully them. Additionally, proper feeding is crucial to prevent instances of cannibalism.
It is important to constantly assess the health of your hermit crabs and look for any signs of trouble, as the vast majority of health problems stem from poor care, such as improper feeding, inadequate water conditions, and inadequate maintenance.
Coenobita variabilis can make wonderful pets for many years, but it’s important to remember that they require special care and attention.
Therefore, before acquiring these animals, make sure you are committed to providing them with the necessary care they need.
- Harvey, Alan W. “Abbreviated larval development in the Australian terrestrial hermit crab Coenobita variabilis McCulloch (Anomura: Coenobitidae).” Journal of Crustacean Biology12, no. 2 (1992): 196-209.
- Kato, Saori, Katsuyuki Hamasaki, Shigeki Dan, and Shuichi Kitada. “Larval development of the land hermit crab Coenobita violascens Heller, 1862 (Decapoda, Anomura, Coenobitidae) described from laboratory-reared material.” Zootaxa3915, no. 2 (2015): 233-249.
- Hamasaki, Katsuyuki, Saori Kato, Yu Murakami, Shigeki Dan, and Shuichi Kitada. “Larval growth, development and duration in terrestrial hermit crabs.” Sexuality and Early Development in Aquatic Organisms1, no. 2 (2015): 93-107.
- Martin, Alan W. Harveyy Joel W., and Regina Wetzer. “Phylum Arthrop0da: Crustacea.” (2002).
- Department of the Environment and Energy (DOEE), Australian Government. 2012. Commercial wild harvest of land hermit crabs Coenobita variabilis from north Western Australia (by Merv Cooper’s Crazy CrabsTM). Available from: http://www.environment.gov.au/biodiversity/wildlife-trade/trading/commercial/operations/ merv-coopers-crazy-crabs (accessed 7 February 2018)