Thai Devil Crab – Detailed Guide: Care, Diet, and Breeding

Thai Devil Crab (Cardisoma carnifex) – Detailed Guide Care, Diet, and Breeding

If you are looking for something unique to add to your paludarium or terrarium setup then the Thai Devil Crab (Cardisoma carnifex) can be an interesting choice for you.

Thai Devil Crabs are relatively large terrestrial crabs and can be recommended even for beginners. You will need a 15-gallon tank for a couple of these crabs, with clear water, moderate humidity, and temperature.

Unfortunately, the ecology of this species is poorly researched and much is still unknown about them. As a result, there is a lot of conflicting and sometimes totally false information on these crabs. Therefore, I decided to do my own research on Thai Devil Crabs.

In this guide, I gathered everything that is currently known about this species including ideal tank setups and how to care for them.

Quick Notes about Thai Devil Crab

Name Thai Devil Crab
Other Names
Soapbox crab, Black devil crabs, Purple Thai devil crab, and Brown land crab
Scientific Name Cardisoma carnifex
Type Terrestrial crabs
Tank size (minimum) 15 gallons (~60 liters)
Keeping Easy
Breeding Very Difficult 
Size of the carapace
7 – 12 cm (3 – 5 inches)
Size across the leg span
15 – 20 cm (6 – 8 inches)
Optimal Temperature 22 – 26°C  (~71°F – 79°F)
Aquarium type Terrarium or paludarium 
Water type Saltwater and freshwater bowls
Humidity
60% and higher
Diet Mostly herbivore / omnivore
Temperament Slightly aggressive
Life span up to 8 years
Color Form Maroon to brownish-grey or greyish-blue coloration

False Taxonomy of Thai Devil Crab or Lies on the Internet

Here is my rant so bear with me a little bit.

I don’t take anything for granted I need to know the details, therefore, I check everything. So, when I started searching for more information about Thai Devil Crabs I got very confused because every single article on the Internet mentioned their scientific name as – Clariosoma Camifax.

However, to my surprise, I could not find anything regarding this species in scientific literature. Why?

Because according to the Integrated Taxonomic Information System (ITIS) and similar systems, such species does not exist!

It would not be a problem if somebody misprinted the name … but not everybody at once! Nowadays, people are so eager to publish as many articles as it is possible that they copy, steal, rewrite information without even verifying it anymore.

Obviously, I could not trust anything they say regarding this topic anymore and I had to start the research from the scratch.

It is not Clariosoma Camifax but Cardisoma carnifex.

Habitat of Thai Devil Crab

Cardisoma carnifex is a species of land crab found from the Red Sea and the east coast of Africa, across the Indo-Pacific to the Tuamotus, including the southern islands of Japan and the northern Great Barrier Reef.

In Palawan, it is reported in the municipalities of Magsaysay, Dumaran, Taytay, El Nido, and Puerto Princesa City. It also occurs in coastal regions of northern Australia and the Cocos (Keeling) Islands.

In nature, Thai Devil Crabs habit the landward fringe of the mangroves borrowing in the mud to hide and are well adapted to terrestrial habitats. It is also found throughout the high intertidal grove.

Description of Thai Devil Crab

Thai Devil Crab (Cardisoma carnifex) – Detailed Guide Care, Diet, and Breeding view
photographs by G, H, Tohru Naruse

Thai Devil Crabs can grow pretty big compared to some of the other crab species available in aquarium stores.

The carapace of an adult crab can grow to about 7 – 12 cm (or 3 – 5 inches) long, with a leg span up to 6 – 8 inches (about 15 – 20 cm) or even more. The total weight can reach 1 pound (or 480 grams)!

Therefore, it will be better to give them extra space in your tank in case they grow a little larger than expected.

Distinguishing characteristics:

  • Mostly maroon to brownish-grey or greyish-blue coloration which gradually disappears towards the sides. Young and newly molted crabs have different shades of purple color, which makes them quite similar to Rainbow crabs.
  • The ventral side is cream or yellow-colored.
  • Dimorphism in claws (in males, one claw is significantly bigger).
  • The claws have almost the same coloration as the carapace. The extreme tips of the fingers are cream-colored.
  • Heart-shaped body.

Note: The name Cardisoma comes from Cardi = heart and soma = body.

Interesting fact: Crabs in the genus Cardisoma are able to detect small vibrations on the ground within the range of 10–1500 Hz and 70 dB. Visual acuity increases with body size due to an increase in both the number and diameter of ommatidia (optical units that make up the compound eye of a crab).

Lifespan/Longevity of Thai Devil Crab

Currently, there is no data available on the maximum lifespan for Thai Devil Crabs (Cardisoma carnifex) in the wild.

However, in captivity, they can live at least 5 – 8 years, if appropriately cared for.

Behavior of Thai Devil Crab

Cardisoma carnifex is a fully terrestrial species. In the wild, they can be found many kilometers away from the sea.

However, in order to maintain an optimal moisture level, they construct deep burrows. According to the study, their burrows can reach up to 2 m (almost 7 ft.) below the soil surface, terminating in a chamber at the level of the water table.  A very approximate volume of sediment extracted per burrow was calculated for the average burrow diameter giving 778 cm3 (0.2 gallons).

They do not like to change their homes and often live there for their lifetime.

Although these crabs appear to be terrestrial, they have modified lungs and require high moisture to breathe. This is the main reason why they dig such deep burrows.

Like most crab species, Thai Devil Crabs are natural loners. These crabs are not social and do not need to be kept in groups. They usually become more aggressive as they age and there is very high chance that will fight fellow members of their own or any other species.  

They are not strictly nocturnal animals. These crabs are relatively active during the night and day. Thai Devil Crabs are not timid.  

Features:

  • Social: No
  • Active: Yes
  • Peaceful: No
  • Burrowers: Yes 

Feeding Thai Devil Crab

Stomach content analysis shows that Cardisoma carnifex are primarily herbivorous preferring tender leaves, fruits, berries, flowers, etc. However, it does not exclude the omnivorous nature that allows them to feed on a wide variety of foods, including small prey.

In captivity, for the best growth, Thai Devil Crabs need a good mix of meats and vegetation. Their feeds should contain protein at a level of about 10 – 15% of the diet.

Foods Thai Devil crabs will enjoy (examples with links to check the price on Amazon), for example:

Leaves (for example, Almond leaves, dead beech, oak leaves, etc.) should always be on the menu, as they feed on these and require the detritus from the leaves. 

Interesting fact: There have been reports that some land crabs (including Cardisoma carnifexis) are poisonous but this is almost certainly associated with their diet, as these herbivorous crabs sometimes consume poisonous plants. Once they are kept for short periods and their guts are empty, however, they are safe even for human consumption.

Features:

  • Diet Type: Mostly herbivore / omnivore
  • Food Preference: Leaves and plants
  • Feeding Frequency: Daily 

Avoid giving your Thai Devil Crabs anything:

  • acidic,
  • salty,
  • spicy,
  • fried,
  • smoked,
  • sweets (like candy),
  • flour (including bread).

It is not good for their digestion and health.

You can also read my articles:

How often should We Change the Food?

You can leave their food for 24 hours before removing it. Leaves can be left for weeks in the tank.

Make sure that whatever Thai Devil Crabs do not consume in one day is removed to prevent moles. Keep in mind that these crabs like to store food in their burrows.

How often should We Change the Menu?

Do not give them the same food for weeks. Ideally, you need to change their diet at least every week.

Do Thai Devil Crabs Need Calcium?

Yes, they do not calcium. As with all crustaceans, calcium is a crucial component of a Thai Devil Crabs’ exoskeleton and overall health.

Calcium can be found in kale, broccoli, spinach, cuttlebones, eggshells, figs, wonder shells, oyster shells, seaweed, seeds, insects, etc.

Always keep a small piece of Cuttlefish bone in their enclosure. Supplement their diet and make sure they get enough calcium (for the exoskeleton) by regularly feeding specialized invert foods.

Cuttlefish bones – link to check the price on Amazon.

I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.

Are Thai Devil Crabs Plant Safe?

No, these crabs are not plant safe. They are mostly herbivorous. So, they will eat, cut, and uproot everything that is possible in your tank.

Keeping and Housing Thai Devil Crab

Thai Devil Crab (Cardisoma carnifex) – Detailed Guide Care, Diet, and Breeding profile
photo by David Monticelly

Once again, I will have to warn everybody – almost everything you may see in other articles or wikihow is wrong! Following their instruction is a sure recipe for a disaster.

Cardisoma carnifex are not freshwater crabs or aquatic crabs. They are land crabs. You cannot keep them in small tanks. They require a specific setup to thrive.

The good thing though is that these crabs are tropical and hardy and can survive in your learning curve.  

Tank Size:

Make sure to keep Thai Devil Crabs in large tank setups because of its growth potential. Hence, a 15 gallon (~60 liters) is the minimum recommended tank size. These crabs need a lot of surface area to roam.

As adults, one male and one female may be kept together in the same enclosure of 40 gallons (180 liters) or more, but two adult males would need far more space to reduce territorial fighting.

Thai Devil Crabs are very good escape artists. It is good to have your tanks covered as much as you can. They are also pretty strong and can move light lids, so keep that in mind.

Land vs Water Ratio:

Thai Devil Crabs are not aquatic; they are terrestrial crabs. Ideally, the land area should take at least 90% of the space in your tank or even more.

·      Substrate:

The tank should be filled with a combination of moist sand or mud into which they can burrow.

In order 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. However, not so wet that it drips or pools water.

To get “sandcastle consistency”, a mixture of cocofiber and sand will be the best option for Thai Devil crab setups.

Tip: There is a simple trick to test the consistency. Take a pencil and stick it all the way down and pull 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 in order to keep it moist enough since the moisture in it will evaporate over time.

Important: Do not ever use saltwater to maintain moisture as salt does not evaporate and can lead to a harmful salt build-up.

How Deep should be the Substrate in Thai Devil Crab Setup?

In the wild, these crabs are known to burrow very deep (up to 2 m or 7 ft.). Therefore, the deeper the better. I’d start with at least 10 cm (4 inches) deep.

Substrate options (check the price to Amazon): 

Water Bowl and Water Type

Thai Devil crabs do not need a lot of water. So, instead of creating a complex tank setup, you can use water bowls.

The only thing that you need to keep in mind – these bowls should be deep enough to completely submerge your crabs.

Thai Devil crabs are mangrove crabs. Even though they can suffice with freshwater, it would be better to provide them with:

  • a bowl of freshwater and
  • a bowl of saltwater.

Drinking, or spooning up water with the chelae to the mouthparts, has been documented in Cardisoma carnifex.

To prepare saltwater you can use Instant ocean marine salt (check the price on Amazon). This is a great choice. It is pretty cheap and will last very long. You only need about a half cup of Instant ocean marine salt per gallon.

Note: Do not ever use simple aquarium salt or table salt!

Regarding freshwater, ideally, you need to give them something like bottled spring or distilled water.

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 (link to check the price on Amazonwill remove also toxic gases, bind to heavy metals, any ammonia, nitrites, or nitrates present for up to 48 hours.

Temperature

The range of optimal temperatures for Thai Devil crabs is anywhere between 71 – 79 °F (22 – 26 °C). They do prefer a warm and humid environment.

If you decide to use a heat pad, it should cover 1/3 (or less) of the tank so that crabs could move from warmer to colder places anytime they want. This allows your crabs to regulate their body temperature to their needs.

Humidity

Thai Devil crabs are pretty resilient to humidity fluctuations.

This is another reason why they are easy to care for. However, for optimal conditions, it is still recommended to keep the humidity around 60% or higher.

Humidity and Thermometer (links to Amazon):

Lighting

No special requirements. You may not even need one.

Decorations and Hiding Spots

Thai Devil crabs will appreciate all types of leaves, rocks, wood, plants, PVC pipes, and other decorations to enrich the environment in your tank. It is very important to minimize stress to your crabs by giving them a lot of places to hide.

This is also critical for the molting process!

Thai Devil Crab and Molting Cycle

The molting process (the molt cycle) is the process by which a crab grows. Because crabs have an exoskeleton, they must molt (shed the old exoskeleton) in order to grow. It also allows them to restore lost limbs.

This process consists of 4 phases:

  1. pre-molt,
  2. molt,
  3. post-molt.
  4. inter-molt.

For more information, read my article “Crabs and Molting Process”.

Important:

  • NEVER disturb your crabs when they are about to molt. Do not panic even if you have not seen your Thai Devil crabs for a few days in a row! Give it time. This is the most stressful moment in its life.
  • Keep putting and replacing food in the tank! You never know when they can come up from the molt.
  • Keep giving them calcium-rich food.
  • Also, do not remove the old exoskeleton from the tank. It contains lots of minerals and your Thai Devil crabs will eat it later.

Rules: How to Care and Handle Thai Devil Crab:

  • Thai Devil crabs are not pets you can play with. Do not take them out just because you want to.
  • Thai Devil crabs should never be lifted up by their legs or claws! They can lose a limb by autotomy.
  • Do not leave uneaten food for too long. It can cause smell and bacteria in their enclosure. Remember, these crabs like to store uneaten food in their burrows.
  • Provide as many hiding places as you can.
  • The substrate should be based on sand and Eco-earth to give them a homely feeling.
  • Make sure the lid of the tank is closed tightly so that they cannot escape it.

Thai Devil Crab – Male and Female Differences

Cardisoma carnifex are sexually dimorphic. There are a few indicators that give away the gender of the animal.

  1. Claws. Dimorphism is confirmed with the major chelae of male crabs reaching larger sizes than those of females.
  2. Size. Males are a little bit bigger than females.
  3. Abdomens. Different shapes of the abdomens. Males have a narrow and slimmer plate (triangular) while females have a broad plate on their belly.

Breeding Thai Devil Crab

Thai Devil Crab (Cardisoma carnifex) – Detailed Guide Care, Diet, and Breeding breeding with eggs
©Anne Hoggett: Cardisoma carnifex at Lizard Island with eggs

Several spawns per year may occur with spawning season varying with location within the range. Males mate with mature females. Fertilization is internal.

After approximately 2 – 3 weeks the eggs will hatch and must be released into saltwater for the larvae to survive. Although Thai Devil crabs can be found many kilometers inland, they must return to the sea to spawn and release their planktonic larvae.

The female Cardisoma carnifex releases larvae in large quantities 3 days before the full moon and large larval release migrations peaking 2 days after the new moon, just after dark.

Eggs hatch into free-swimming larvae with several zoeal stages and 1 post-larval or megalopa stage.

Each female releases between 350.000 – 450.000 eggs. Typical development time from hatching to the first crab’s stage is from 22 to 25 days.

After a period in the planktonic larvae, they return to the mainland as megalops or first crab stages.

After that, they start living within burrows of adult crabs, in diverticula starting from the main branch of the burrow.

Nothing is known about when they start to dig their own burrows or how they avoid being cannibalized within the adult burrows. According to the same study, young crabs spend at least 3 years in this environment, probably feeding on leaves remaining from the adult meals. Their gill chamber structure is much less adapted for air-breathing than that of the adult.

Thai Devil Crab and Suitable Tankmates

Even though Thai Devil crabs are not extremely aggressive as some other crab species, they are still not peaceful and inoffensive.

They are antagonistic and territorial (especially males). Males are extremely likely to fight when housed together. Therefore, it can be risky to house multiple crabs in the same tank.

Ideally, they should be placed in a tank alone or with other Thai Devil crabs of another sex.

In this case, crabs should be well-fed at all times and there must be a lot of hiding places. Nonetheless, even having lots of hiding places in the tank and keeping them well-fed will not guarantee peaceful coexistence.

In a paludarium setup, it is possible to keep dwarf shrimp, snails, and fish with them. Thai Devil crabs usually do not show any interest in going into the water.

In Conclusion

In recent years, interest in alternative species in aquariums, paludariums, terrariums, etc. has increased considerably.

Unfortunately, little is known of the life history of Cardisoma carnifex. Combine it with wrong and/or totally false information in other articles regarding Thai Devil crabs care and, as a result, it only creates more confusion and misunderstanding.

Thai Devil crabs are mangrove crabs; they are not aquatic. They spend almost all of their time inland. These crabs have a lot of character, personality, and can be a great addition to your home tank. They will certainly keep you occupied.

References:

  1. QUINN, N. J., B. L. Kons, K. DIBLE, and U. MEISCHNER. 1991. Reproductive behavior of Cardisoma carnifex (Herbst, 1794) (Brachyura: Gecarcinidae) at Lizard Island, Great Barrier Reef. Mem. Queensl. Mus. 31: 399.
  2. Local Ecological Knowledge and Biology of the Land Crab Cardisoma hirtipes (Decapoda: Gecarcinidae) at West Nggela, Solomon Islands. Pacific Science (1999), vol. 53, no. 1: 37-49
  3. An Annotated Checklist to the Commonly Harvested Crabs (Crustacea: Decapoda) from Marine and Brackish Water Ecosystems of Palawan, Philippines. Journal of Environment and Aquatic Resources. 5: 61-82 (2020)
  4. Behavioral Regulation of Hemolymph Osmolarity Through Selective Drinking in Land Crabs, Birgus latro and Gecarcoidea lalandii. Biol Bull 182: 416-423. (June, 1992)
  5. Kormanik, G. A., and R. R. Harris. 1981. Salt and water balance and antennal gland function in three Pacific species of terrestrial crab (Gecarcoidea lalandii, Cardisoma carnifex, Birgus lalro). I. Urine production and salt exchanges in hydrated crabs. J. Exp. Zool. 218: 97-109.
  6. Wood, C. M., and R. G. Boutilier. 1985. Osmoregulation, ionic exchange, blood chemistry, and nitrogenous waste excretion in the land crab Cardisoma carnifex: a field and laboratory study. Biol. Bull 169: 267-290.
  7. Wood, C. M., R. G. Boutilier, and D. J. Randall. 1986. The physiology of dehydration stress in the land crab, Cardisoma carnifex: respiration, ionoregulation, acid-base balance and nitrogenous waste excretion. J.Exp. Bwl 126:271-296.
  8. Land crabs (Crustacea: Brachyura: Gecarcinidae) of Singapore. 14: e2021001. DOI: 10.26107/NIS-2021-0001
  9. Tan AYH & Tan TN (2016) Brown land crab Cardisoma carnifex on Pulau Ubin. Singapore Biodiversity Records, 2016: 129.
  10. Range extension of the land crab Cardisoma carnifex (Herbst, 1796) to further north on the Pakistan coast (Arabian Sea). Zoological Survey Department, Government of Pakistan, Karachi (SP).
  11. Cameron, J.N., 1981. “Acid-base responses to changes in CO2 in two Pacific crabs: the coconut crab Birgus latro, and a mangrove crab, Cardisoma carnifex.” Journal of experimental Zoology 218:65-73.
  12. Harris, RR and GA Kormanik, 1981. Salt and water balance and antennal gland function in three Pacific species of terrestrial crab (Gecarcinus lateralis, Cardisoma carnifex, Birgus latro). II. The effects of desiccation. Journal of Experimental Zoology 218: 107-116.
  13. Kannupandi, T, S. Ajmal Khan, Mercy Thomas, S. Sundaramoorthy and R. NAtarajan , 1980. “Larvae of the Land crab Cardisoma carnifex Herbst (Brachyura: Gecarcinidae) Reared in the Laboratory.” Indian Journal of Marine Sciences 9: 271-277.
  14. Lee, M.A.B., 1988. “Food preferences and feeding behavior of the land crab Cardisoma carnifex.” Micronesica 21: 274-279.
  15. Micheli, F., F. Gherardi, and M. Vannini, 1991. “Feeding and Burrowing Ecology of Two East African Mangrove Crabs.” Marine Biology 111:247-254.
  16. Morris, S. and A.M. Adamczewska, 1996. “Respiratory, acid-base and ion status during voluntary immersion of the air-breathing crab Cardisoma carnifex assessed in situ.” Journal of Experimental Marine Biology and Ecology 206(1-2): 149-164.

2 thoughts on “Thai Devil Crab – Detailed Guide: Care, Diet, and Breeding

  1. Greetings!
    I am so thrilled I found this article! I went to e PetCo and saw three of these in a tank completely submerged with no availability to climb out! I have been looking for this type of pet.
    If I get a 20+ gallon tank and fill it with the moist sand etc. can they do well with a bowl to submerge in, or do I need to have a “beach” style set up and get a filter etc.?
    If you can offer any advice I would love to do this the smart way and give the animals the best possible chance!
    Kindest regards,
    John

    1. Hi John Peskey,
      First of all, I have little to no trust in Petco.
      The point is that you need to check that this is the species they claim to be. Yeap, there are way too many mistakes when it comes to crabs.
      It is quite possible that this is not Cardisoma carnifex and some kind of semi-aquatic or aquatic crab.
      If it is Cardisoma carnifex, you do not need a filter, just replace the water in the bowl.
      As for the sand, I would mix it with coconut fiber. This way it will maintain its shape whereas sand will collapse (I am talking about burrows).
      Best regards,
      Michael

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