Thai Devil Crab Care Guide | Diet, Habitat, Breeding, Tank Mates!

Jul 4, 2022

Thai Devil Crab Care Guide

If you’re looking for a crab that looks stunning but is also super hardy, I think you have come to the right place. Thai devil crab might just be the perfect addition to your paludarium or terrarium. 

I find these crabs super interesting. Do you know they can live in three different environments – land, freshwater, and saltwater?

But unfortunately, very little is known about the ecology of this species. 

We are still in the dark. Consequently, there’s a lot of conflicting and sometimes false information doing the rounds of the internet. 

I’ll be honest – I’ve never raised Thai devil crab before. However, I have spent hours shuffling through the pages of whatever little info is available to write this blog. 

I can confidently say this article on Thai devil crab encapsulates all the information currently available to us. I’ve penned down a care guide that will come in handy if you’re planning to bring home a Thai devil crab. 

Thai Devil Crab At A Glance 

  • Name: Thai devil crab 
  • Scientific Name: Cardisoma carnifex
  • Other Names: Soapbox crab, Black devil crab, Brown land crab
  • Lifespan: 8 years 
  • Carapace size: 3-5 inches (7-12 cm)
  • Size across the leg span: 6-8 inches (15-20 cm)
  • Color: Grayish-blue, maroon, or brownish-gray
  • Temperament: Semi-aggressive 
  • Care Level: Easy
  • Breeding: Difficult
  • Minimum Tank Size: 15 gallons (60 liters)
  • Temperature: 71-79 degrees F (22-25 degrees C)
  • Setup: Paludarium or terrarium 
  • Diet: Omnivore
  • Humidity: 60% or higher 
  • Water: Saltwater and freshwater 

Thai Devil Crab Origin 

Although we don’t know much about Thai devil crabs, their popularity in the hobby is commendable. Especially over the last decade, they’ve become quite famous and are now a common sight in just about any LFS. 

These crabs are indigenous to the Red Sea and eastern coast of Africa, southern islands of Japan, Great Barrier Reef, northern Australia, and Cocos islands. 

Breeding Thai devil crabs are difficult. It requires Herculean effort to get them to breed. Therefore, the crab you see at your LFS was most likely caught from the wild. Unfortunately, breeding them in captivity is something humans haven’t mastered yet. 

Thai Devil Crab Name Debate 

Most sites using the name Thai devil crab stated that the crab’s scientific name is Clariosoma Camifax. So naturally, I typed in the name on Google but to no avail. 

There wasn’t single scientific literature on this species. 

I almost gave up and stopped writing, but then I had a Eureka moment. So I searched the name in the Integrated Taxonomic Information System directory and found out that such a species doesn’t exist at all!

It took me a couple of hours to find out the crab has an entirely different name.

So, it’s not Clariosoma camifax. It is called Cardisoma carnifex. 

How Long Do Thai Devil Crabs Live? 

Thai devil crabs live for 8 years on average. However, when I dug through some forums and discussions, I came to know that most don’t make it past their 5th birthday. 

So, I guess 8 is the maximum number of years these crabs can live based on what’s known about their lifespan. We don’t know much. 

Recommended Article:

What Do Red Claw Crabs Eat? Feeding Guide 101

Thai Devil Crab Appearance 

The Thai devil crab’s scientific name tells a lot about its appearance. The name is Cardisoma carnifex. And the word “cardisoma” can be separated into two parts: ‘cardi’ meaning heart, and ‘soma’ meaning body. So, as the moniker gives away, the crab has a unique heart-shaped body. The body is divided into two chief parts: carapace and leg space. 

Thai Devil Crab Size 

These crabs don’t grow particularly big. The carapace of an adult crab is about 3-5 inches (7-12 cm) long. On the other hand, the legs are a bit longer – growing around 6-8 inches (15-20 cm) long. 

And by the way, they can weigh over 1 pound (480grams)! 

Thai Devil Crab Colors 

Although also known as purple Thai devil crap, the crustacean comes in 3 different shades: purple, brownish-gray, and grayish-blue. The color fades towards the sides. 

The ventral side has a muted beige color. The claws almost have the same coloration as the carapace. But the tips of the fingers have a cream color.

Newborn and newly molted crabs come in varying shades of purple. And that’s what they get their name from.

Here’s an interesting fact about Thai devil crab.

Crabs from the Cardisoma genus can detect small vibrations in the ground within the range of 10-1500 Hz and 70 dB. 

Also, visual acuity increases with body size because it increases the number and diameter of ommatidia (optical units that make up the crab’s compound eye).

Thai Devil Crab Male VS Female 

Sexual dimorphism between male and female Thai devil crabs is subtle yet loud. The main difference is that males have significantly bigger claws than females.

Also, males are quite bigger than females. 

Another differentiating factor is that males and females have differently shaped abdomens. Males have a narrow and triangular plate, whereas females have a broad plate on their belly. 

Thai Devil Crab Temperament 

Contrary to popular belief, Thai devil crabs are a fully terrestrial species. Thus, they’re often found several kilometers away from the sea. 

But to maintain the optimum moisture level in the body, the crabs dig deep burrows. One particular study found out that their burrows can reach up to 2 meters (almost 7 ft) deep below the ground. 

Although Thai devil crabs are terrestrial, they have modified lungs and need moisture to breathe. This is one of the reasons why they dig deep burrows.

These crustaceans do not like change. So once they’ve settled down and built a home, they stick to it for a lifetime. 

Also, in line with typical crab fashion, Thai devil crabs are solitary creatures. They don’t thrive in groups. They are not social like that and definitely don’t get lonely. 

Hobbyists report that the crab gets crankier as they age. So, there’s a possible chance they will fight off each other if kept in the same enclosure. 

Like most crabs, Thai devil crabs are nocturnal creatures. They stay awake and active at night. It’s reported that the crabs’ nocturnal behavior is an adaptation to avoid predators, dehydration, and higher temperatures. 

Tl; Dr

  • Active? Yes 
  • Social? No
  • Aggressive? Yes 
  • Peaceful? No

Thai Devil Crab Tank Mates 

Even though Thai devil crabs are not extremely aggressive as some crab species, they’re still far from being peaceful. So, it’s better to err on the side of caution when choosing tank mates. 

They are quite hostile and territorial – especially the males. If kept together in the same enclosure, they’ll probably fight to death no matter how big the enclosure is. 

In a paludarium, the crab can cohabitate with dwarf shrimps, snails, and fish. Thai devil crabs seldom go into the water – so they won’t show any interest in other creatures. 

However, the crab should always be well-fed, and plenty of hiding places should be strategically created. 

Thai Devil Crab’s Diet

Although Thai devil crabs are known as omnivores, research on their stomach content showed that these crustaceans heavily prefer plant-based food like leaves, fruits, berries, and flowers. They eat by grazing. 

To ensure proper health and the best growth rate in captivity, feed them a varied diet consisting of plant and meat-based food. Protein should make up around 15% of their total diet. 

Here’s a list of fruits you can give them: 

  • Sweet apples 
  • Melons 
  • Mangos 
  • Bananas 
  • Apples 

Here’s a list of veggies you can give them: 

  • Leafy greens
  • Cabbages
  • Carrots
  • Broccoli
  • Lettuce
  • Cucumber
  • Peas
  • Corn
  • Spinach
  • Squash

Here’s a list of protein-rich food you can give them:

  • Shrimp pellets 
  • Fish food 
  • Shrimp food 
  • Brine shrimp
  • Fruit flies 
  • Crickets 
  • Bloodworms 
  • Detritus worms
  • Bloodworms

How Often Should You Change The Food?

Make sure to remove any uneaten food from the tank after 3 days, and don’t forget to inspect why the crab isn’t eating. 

How Often Should You Change The Menu?

Variety is important to ensure the crab gets all the nutrients it needs. Since they are omnivores, you have many options to choose from. Give different kinds of food once every couple of days. 

Don’t give the crab the following food:

  • Dairy 
  • Flour-based food
  • Acidic food 
  • Spicy food
  • Salty food
  • Fried food 
  • Smoked food

Can We Eat Thai Devil Crab?

Some reports have shown that Thai devil crabs are poisonous and shouldn’t be eaten. But this has everything to do with their diet. 

If they consume poisonous plants, they will likely become poisonous too. However, once they are kept on a fast for some time and empty their stomachs, they can be safely consumed. 

Caring For Thai Devil Crab 

Before I start off, here’s a little disclaimer. Everything else you find on caring for these crabs from aquarium blogs and wikiHow should only be taken with a pinch of salt. 

I don’t want to sound cynical, but I was quite amazed at the amount of false information circulating on the web – even from credible publishers like wikiHow. 

For starters, Thai devil crabs are not freshwater or aquatic, as indicated in the wikiHow article. Instead, these are strictly land crabs. 

Second, you cannot keep them in just about any small tank. They aren’t exactly high-maintenance but require a specific setup to thrive. 

Don’t worry – it’s not as hard as I’m making it to be. Haha. My apologies! 

These are tropical crabs and thus quite hardy – as hardy as they come. They will most likely survive through your learning curve. 

Minimum Recommended Tank Size For Thai Devil Crab 

As discussed above, these crabs can grow quite big – especially their claws. Therefore, you need a big enclosure to begin with. While most blogs recommend that a 5-gallon tank suffice, I suggest going bigger. 

Get at least a 15-gallon tank. 

You’d need an even bigger tank if you plan to keep a male and female Thai devil crab. I’d say about 40 gallons. 

And if you plan to keep 2 males together, I’d recommend against it. They’ll fight, and one of them will bite the dust. But if you still insist, you’d need a far bigger tank. 

Also, since these crabs make excellent escape artists, don’t forget to put on a heavy and fitting lid. Remember that they are quite strong and can easily move light lids. 

Land VS Water Ratio For Thai Devil Crab 

Since Thai devil crabs are terrestrial beings, I’d say the land area should take up at least 80% of the total tank space. 

Substrate For Thai Devil Crab 

Since Thai devil crabs need dampness to breathe and burrow to live in, it’s best to use moist sand or mud as substrate. 

The substrate should always be kept moist to enable the crab to dig underground and make a cave. To give you an idea, the substrate should hold its shape when you squeeze it. But it shouldn’t be dripping. 

A hobbyist recommended mixing sand with coco fiber to achieve the ‘sandcastle consistency.’ 

Here’s a simple tip: to test the consistency of the substrate, stick a pencil all the way down and pull it back up. If the tunnel doesn’t collapse, your substrate is good enough. 

You’ll need to maintain the substrate once every few days by spraying dechlorinated water to keep it moist as the moisture evaporates over time. 

Remember to not use saltwater to maintain the substrate’s dampness. Salt doesn’t evaporate and can lead to health complications.

How Deep Should The Substrate Be For A Thai Devil Crab?

In the wild, Thai devil crabs burrow very deep tunnels – up to 2 meters (7 feet) deep. So, the substrate should be at least 4 inches (10 cm) deep in captivity

Here are some substrate options to check: 

Substrate options (check the price to Amazon): 

Water For Thai Devil Crab 

Since Thai devil crabs are terrestrial beings, they don’t require plenty of water. Therefore, you can save yourself the hassle of creating a complex tank setup and simply add two water bowls. 

Bear in mind that the water in these bowls should be deep enough to completely submerge the crab. 

Since Thai devil crabs are mangrove crabs, it’s better to offer a bowl of saltwater and a bowl of freshwater.

Interestingly, these crabs have been documented to drink or spoon water with chelae to the mouthparts. 

Here’s a quick link to marine salt on Amazon. It’s cheap and enjoys good reviews. 

Reportedly, you just need about half a cup of marine salt per gallon. 

You cannot use table salt or simple aquarium salt. 

As for freshwater, you can give them distilled water or bottled spring water. I’d recommend against using tap water since it contains chlorine that is toxic to crabs. 

If you need to use tap water, dechlorinate it first using a reliable conditioner like one from Seachem. 

Temperature For Thai Devil Crab

The temperature for Thai devil crab should range between 71-79 degrees F (22-26 degrees C). These crabs love warm and humid environments. 

If you plan on using a heating pad, it should cover just one-third of the tank at max so the crab can shift to a cooler area if it’s too hot. 

Humidity For Thai Devil Crab 

Good news – these crabs are pretty resilient to humidity fluctuations. However, don’t let it be an excuse to keep them in subpar environments. 

Ideally, the humidity should be around 60% or higher. 

Here are a couple of links to Amazon if you want to buy a humidity thermometer:

Lighting For Thai Devil Crab 

You don’t need to make any special lighting arrangements. The room’s lighting will do. 

Decorations For Thai Devil Crab 

It’s best to take inspiration from their natural habitat when decorating the tank setup for Thai devil crab. They will surely appreciate having plants, woods, rocks, leaves, and even PVC pipes in their tank. 

It’s important to provide enough hiding places for the crab to hide away when anxious or overwhelmed. Hiding places are also crucial to facilitate the molting process. 

Thai Devil Crab Molting Cycle

As you already know, molting is the process of shedding an exoskeleton and building a new one to grow. Yep, that’s how it works. It’s also an opportunity to restore lost limbs. 

The molting process has 4 main phases:

  • Pre-molt
  • Molt
  • Post-molt
  • Inter-molt

Here are a few things to keep in mind to facilitate the molting process:

  • Don’t ever disturb the crab when it’s about to molt. Don’t worry, even if you don’t see your crab for a few days. Molting is stressful, and your crab wants to be left alone more than anything. 
  • Even if you don’t see the crab, keep and replace the food routinely in the tank. They’d want to have a good meal after a wearing molting process. 
  • Feed calcium-rich food. 
  • Don’t discard the old exoskeleton. It’s nutrient-dense, and the crab will consume it later. 

Breeding Thai Devil Crab 

Several spawns will occur throughout the year. There’s no rule set in stone when it comes to when the spawning will occur. It can differ with location. 

The fertilization is internal. 

The eggs take anywhere between 2-3 weeks to hatch. After the eggs hatch, the larvae must be released into saltwater. Otherwise, they’ll die right off the bat. 

So, although it’s true that Thai devil crabs are terrestrial beings, they must return to the sea to breed and release their planktonic larvae. 

The matriarch releases the eggs in large quantities exactly 3 days before the full moon. Each female can release between 350-450 eggs. 

The eggs take 22 to 25 days to hatch into life’s first stage. 

The eggs will hatch into free-swimming larvae that live through multiple zoeal stages and 1 megalopa or post-larval stage. 

The crab will eventually return to land as it grows and starts living under burrows they will dig meticulously. 

Naturally, it’s incredibly hard to breed Thai devil crabs in captivity since they tend to synchronize reproduction to the lunar-tidal cycle, and it’s impossible to recreate this environment in captivity. 

Besides that, you also have to set up a new saltwater tank with very specific water parameters. And don’t even get me started on caring for the larvae. 

If you want more crabs, just buy them. And just so you know, they don’t cost much. So, it’s not worth investing time and money into breeding them. 

Final Words: Thai Devil Crab Care Guide 

Very little is known about the lives of cardisoma carnifex. And unfortunately, more than half of the information on the internet is half-baked. The first thing to remember is that Thai devil crabs are not aquatic crabs like many believe – they are mangrove crabs. They spend the majority of their time on land. 

Keep the following in your mind:

  • Thai devil crabs don’t thrive on human attention as dogs do. Also, they’re no toys to play with. Don’t take them out of the tank and handle them just because you want to. 
  • The crab should never be lifted up by their claws. They may lose a claw. 
  • The crabs store uneaten food in the burrow. But make sure you take them out and discard them to maintain the tank’s hygiene. 
  • Offer as many hiding places as you can. 
  • The tank’s lid should be closed tightly, so they don’t escape. 


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rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.