The Marble crab (Metasesarma obesum) is a relatively rare land crab that a lot of hobbyists would like to acquire because of its rare and unique design.
When I saw them for the first time, I got curious about these beautiful crabs and decided to do some research. To my pleasant surprise, I found out that Marble crabs are no different to care for than any other terrestrial crab species and can be recommended even for beginners. You will need a 5-gallon tank for a couple of these crabs, with clear water, high humidity, and temperature.
Note: I need to start off by mentioning that information on Marble crabs in scientific literature is scanty. Generally, in my guides, you can find a lot of references to official studies, researches, and experiments. The point is that I want to provide as much information as I can for everyone who reads them.
This time it was so hard to find anything that I had to search for information on German forums, so the guide is purely based on the experience of people who owned them.
This profile guide will give a special look into this remarkable species. If you’re curious about Marble crabs and their behavior, life span, growth, feeding, handling, etc., read on.
Quick Notes about Marble Crab
| Name | Marble crab |
| Other Names |
Green Emerald Crab, Batik Crab, Batik Vampire Crab, Emerald Land Crab or Mottled Crab |
| Scientific Name | Metasesarma obesum (previously Sesarma obesum) |
| Tank size (minimum) | 5 gallons (~20 liters) |
| Type |
Terrestrial crabs |
| Keeping | Easy |
| Breeding | Very Difficult |
| Size (carapace) | 1.5 – 2.5 cm (0.5 – 1 inch) |
| Size across the leg span |
4 – 5 cm (1.5 – 2 inches) |
| Optimal Temperature | 24 – 28°C (~75°F – 82°F) |
| Water type | Freshwater and saltwater bowls |
| Moisture | 70% and higher |
| Substrate | 1 – 2 inches (2.5 – 5 cm) |
| Diet | Mostly carnivore/omnivore |
| Temperament | Slightly aggressive |
| Life span | up to 3 years |
| Color Form | Cream base color with different colors and patterns on their back |
Taxonomy of Marble Crab
In science, the identity of this Indo-West Pacific sesarmid crab species has been particularly difficult.
At first (in 1851), it was originally described from Balabac off northern Borneo as Sesarma obesum. Unfortunately, the brevity of the description has made its precise identity and proper generic assignment difficult to ascertain.
There was even a hypothetical assumption that it could be Holometopus obesus before the species was identified as Metasesarma obesum and moved into the genus Metasesarma.
Habitat of Marble Crab
Marble crabs are Widely distributed in the Indo-Pacific: Zanzibar, Madagascar, Lacca-dive Islands, Mergui Archipelago, Kerala, India, Sri Lanka, Christmas Island, Indonesia, Philippines, Taiwan, southern Ryukyu Islands (Iriomote and Miyako islands), Guam, New Guinea, and Tahiti.
These crabs are often reported from islands with wide gravel or sandy areas without rivers or freshwater sources, as is typical for the islands north of Borneo.
Marble crabs often occur in terrestrial boulder area somewhat remote from the beach line. The crabs hide under stone or coral rock during the day.
They also inhabit mangrove areas and like the cover and protection of a dense forest floor.
Description of the Marble Crab
All Marble crabs are similar in shape, having a smooth carapace and a square-shaped body. Their eyes are located at the end of two movable eyestalks located in the center of the carapace.
The average size (shell width) of the adult Marble crab is only about 1.5 – 2.5 cm (0.5 – 1 inch) long. Across the leg span, they barely reach 4 – 5 cm (1.5 – 2 inches).
Even though these brightly colored decapods have earned this common name from their greenish coloration of the carapace, you may be surprised how many color morphs they have.
Each Marble crab has a different color, pattern, and varies in appearance. Some of them may not have any green color at all.
Marble crabs live rather brief lives of no more than 1.5 – 2 years (up to 3 years in captivity under optimal conditions). In a poorly maintained environment, these crabs can suffer and die prematurely.
Marble Crab Behavior
Although Marble crabs are considered to be social animals and benefit from being in the company of their own, it is still not that simple.
Despite their small size, Marble crabs are not completely peaceful and inoffensive. They have complex territorial interactions and in the overcrowded tank will easily regulate their number.
That kind of behavior can be a problem for those who prefer to keep different animal species in the same enclosure. They do not like intruders of other crab species.
For example, they are a little bit bigger and more aggressive than Geosesarma species (such as Vampire Crab, Tangerine-head crab, etc.)but smaller than the Red Apple crab (Metasesarma aubryi). So, it would not be a good idea to keep them together.
Generally, Marble crabs are not very shy. They like to explore every nook and cranny in the tank.
They are not active diggers. In nature, these crabs prefer to use pre-made burrows dug up by other animals, while in captivity, they can dig some small dens in the substrate.
Marble crabs are not destructive. You should not worry that they will redecorate your paludarium to their liking.
They are mostly nocturnal, however, periodically, they can also be active during day time.
Some Marble crab owners reported that with time their pets could even recognize them and did not fear their presence anymore.
Feeding Marble Crab
Marble crabs are natural-born scavengers. They are omnivores and opportunistic eaters that will eat anything they can find! They will gladly spend all their time wandering around the tank and scavenging for food.
In captivity, Marble crabs will eat detritus, leaf litter, seeds, etc. However, for the best growth, feeds should contain protein at a level of about 60 – 70% of the diet.
| Marble crabs are not vegetarians and require a lot of protein.
Interesting observation: These crabs catch eats flies, mosquitoes, and some other insects.
Foods Marble crabs will enjoy (examples with links to check the price on Amazon), for example:
- Shrimp pellets.
- Shrimp Granules.
- Fish food (TetraMin® flakes, etc.)
- Shrimp food (Hikari’s crustacean food like Hikari Shrimp Cuisine, Algae wafers, Brine shrimp, etc. )
- Frozen blood worms.
- Crushed snails.
- Small earthworms.
- Detritus worms.
- Brine shrimp.
- Vegetables (like spinach, peas, squash, leafy greens, etc.)
- Leaves.
It is very important to vary their diet to stimulate their digestive systems and make sure they get all the nutrients they need.
Note: Regularly give them Almond leaves, dead beech, oak leaves, etc. as they feed on these and require the detritus from the leaves.
You can also read my articles:
- Indian Almond Leaves and Alder Cones in a Shrimp Tank.
- How to Blanch Сucumbers and Zucchini for Shrimp, Snails and Fish the Right Way
- What Do Crabs Eat and How to Feed Them?
How often should We Change the Food?
You can leave their food for 24 hours before removing it. Just make sure that whatever Marble crabs do not consume in one day is removed to prevent moles.
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 Marble Crabs Need Calcium?
As with all crustaceans, calcium is a crucial component of a Marble Crab’s exoskeleton and overall health.
Calcium can be found in kale, broccoli, spinach, cuttlebones, eggshells, figs, nuts, wonder shells, oyster shells, seaweed, seeds, insects, etc.
Always keep a small piece of Cuttlefish bone in their enclosure. Marble crabs need calcium. Supplement their diet and make sure they get enough calcium (for the exoskeleton) by regularly feeding specialized invert foods.
| I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”. |
Cuttlefish bones – link to check the price on Amazon.
Keeping and Housing Marble Crab
Marble crab care is quite easy compared to a lot of other invertebrates. These decapods are not high-maintenance pets and adapt well to life in captivity and can stay pretty healthy in most situations.
Of course, you still need to address their core needs! These animals require a very specific environment if you want them to be happy and healthy.
Here are some care guidelines to help you out:
Tank Size:
Tank size is important to the Marble crabs. They are territorial and like space to roam around, as well as a varying amount of terrain to hide in and escape to from things like unwanted attention or sunlight.
The minimum recommended tank size for a few Marble crabs (1 male and 1 or 2 female) is a 5-gallon (20-liter) tank.
Do not take it lightly, overcrowding is a major source of stress for crabs. Eventually, it can lead to health problems and aggression. This is particularly important when you have more than one male, as they are more aggressive.
A group of up to 4 – 5 crabs can live very comfortably in a simple 10-gallon (40 L) tank. A tank like this one could work for you.
Add 1 to 2 more gallons (or 4 – 8 Liters) of tank space per each additional crab.
Tank Lid:
Whatever size of tank you go with, make sure it has a stable lid! Marble crabs are excellent escape artists! They can and will climb out of their tank when given the chance.
Substrate and Decorations
To mimic their natural habitat, Marble crabs in captivity need a proper substrate and decorations so that they can have their individual spaces if there is more than one crab.
The option for the substrate:
- coconut fiber,
- soil,
- peat,
- sand.
The substrate should be moistened to sand castle consistency at all times. It will also help you to maintain a proper level of humidity.
Tip: You can test the consistency of the substrate with a pencil. Stick it all the way down and pull back up. If the tunnel does not collapse, your substrate is fine.
Hiding spots should be installed in the tank for giving them places to hide. For that ceramic flower pots, flat stones, PVC pipes, and pieces of bark will do the job.
You can add some rocks, plastic balls, plastic tunnels, crab huts, plastic plants, fish netting, and other decorations to enrich the environment.
Plants are good for their setup too.
These crabs love climbing!
Related article:
How Deep should be the Substrate in Marble Crab Setup?
In the wild, these crabs do not dig a lot. Therefore 1-2 inches (2.5-5 cm) will be more than enough.
Substrate options (check the price to Amazon):
Land vs Water Ratio
Let me repeat that Marble crabs are often found in areas without rivers or freshwater sources. They are land crabs and have a clear preference for terrestrial areas.
The land area should take 90% of the space or more.
Water Bowl and Water Type
Because Marble crabs are not aquatic, they do not need a lot of water in their tank. Even more, they cannot stay in water for a long time. They will drown.
Therefore, they will be completely happy with a suitably sized bowl of water available to them 24/7.
The water only needs to be a few inches deep. It should be big enough to completely submerge your crab and nothing more.
It is crucial to provide a variety of surfaces for them to get out of the water. You also can place some rocks or driftwood in the water to create small islands that the crab can climb onto.
What type of water do they prefer?
Some people say that there should be two water bowls (pools) in your Marble crab habitat. One should be freshwater and the other should be saltwater (or brackish). Other hobbyists believe that freshwater will be enough.
There is the truth?
Well, many crab owners reported that these crabs rarely get into any water. In addition, they need saltwater only when they are releasing eggs.
Therefore, if you have a small tank and do not want to breed them (actually, it is close to impossible), they should be fine with the freshwater bowl.
However, for a large tank, I would still go for the saltwater bowl as well.
Note: Do not ever use simple aquarium salt or table salt! To prepare saltwater, I would recommend using 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.
Temperature
The range of acceptable temperatures is anywhere between 71 – 86 °F (22 – 30 °C) with around 75 to 82 (24 – 28C) being optimal.
Ideally, Marble crabs need an enclosure that offers them a hot side and a cold side. This allows your crabs to regulate their body temperature to their needs.
One of the most popular heaters – Zoo Med Repti Therm Under Tank Heater (check the price on Amazon).
Humidity
Marble crabs are used to high-humidity environments and should not be kept in a dry tank. They need moist, and humid air to breathe properly.
They also need a hiding place that is moist—this is where they retreat to when it is time to sleep, rest or molt.
The humidity level should be between 70-90%.
How to keep the tank humid?
- Keep the substrate moist. Fill a plastic spray bottle with dechlorinated water and spray this over the substrate side of the tank at least 2 times a week.
- Provide water for your crabs. Evaporation will automatically increase the humidity level.
- Use a glass top. It will increase the evaporation effect.
If your humidity levels stay too high or too low, it can be fixed by adding more moisture, less ventilation or by adding more ventilation.
This is normally a trial and error process, so expect it to take some adjusting to get it perfect.
Important: Be careful and avoid over humidifying as a saturated substrate can cause mold and infection.
Humidity and Thermometer (links to Amazon):
- Zoo Med™Reptile Terrarium Digital Thermometer,
- Zoo Med Labs Digital Thermometer Humidity Gauge,
- AcuRite 00613 Indoor Thermometer & Hygrometer with Humidity Gauge
Lighting
No special requirements. Marble crabs are nocturnal creatures.
Therefore, lighting should be adapted to the needs of plants in the paludarium or terrarium.
Marble Crab and Molting Cycle
Like all crustaceans, Marble crabs need to molt to grow in size and also regrow any lost limbs.
With time, as they outgrow the existing shell (exoskeleton), they begin to shed their shells off. This process is called molting.
The molting process (the molt cycle) is the most important part of any crab’s life.
This process has 4 phases:
1. pre-molt,
2. molt,
3. post-molt.
4. inter-molt,
During pre-molting periods, most metabolic activities are reduced to a minimum. Marble crabs stop eating and become very lethargic. They need darkness, moisture, and heat to successfully molt.
The pre-molt stage terminates with the molting shedding of the old shell. For that, the crab’s body releases specific hormones to initiate the molting process. This is the shortest stage and the most dangerous for the crab out of four. Depending on how old it is, it usually lasts from a few minutes to several hours.
The post-molt is another critical phase in the molting cycle of Marble crab. They are vulnerable and helpless during and after molting, so it is necessary for them to go into hiding and not reappear until the process is complete and their new carapace has begun to harden.
The inter-molting stage is the last and the longest stage. It is a period when the crab is resting between the molting cycles. The inter-molting periods can be short (weeks) when the crab is young. As the crab ages, these periods will begin to happen further and further apart.
Important:
- NEVER disturb them when they are about to molt. Even if you have not seen your crab for several 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 Marble crab will eat it later.
For more information, read my article “Crabs and Molting Process”.
Some Important Rules Regarding Marble Crab Care and Handling:
- Marble crabs are not pets you can play with. Do not take them out just because you want to.
- Marble 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.
- Decorate the enclosure with as many things as you please because this species loves to hide.
- The substrate should be based on sand and Eco-earth to give them a homely feeling.
- Temperature gradients and heating pads are the best options for keeping Marble Crabs.
- Make sure the lid of the tank is closed tightly so that they cannot escape it.
Related article:
Marble Crabs – Male and Female Differences
With a lot of crabs, it is relatively easy to tell whether they are male or female. Marble crabs are not an exception.
It is a bit easier to tell whether they are male or female by looking at the size and shape of their claws.
- Size. Males are a little bit bigger than females and have larger claws.
- Abdomens. We can differentiate the gender by the shape of their abdomens. Males have a narrow and slimmer plate (triangular) while females have a broad plate on their belly.
Related article:
Breeding Marble Crab
I have to start off by saying that due to many different factors, the breeding process of Marble crabs presents various difficulties. All stages show a very high mortality rate.
So far, there have been no reports of successful breeding Metasesarma obesum in captivity. The most successful attempt ended at the megalopa stage (last stage).
| Currently, the pet industry completely depends on wild-caught species.
In the wild, Marble crabs migrate to the ocean to release eggs that hatch into planktonic marine larvae. Each female may produce hundreds of eggs, however, only a small fraction of them eventually metamorphose and crawl back onto land.
Marble Crab and Suitable Tankmates
Marble crabs can be kept in a group relatively safely, but only under several conditions:
- Males to females ratio (1:3). Males, in particular, are extremely likely to fight and eventually kill one another when housed together.
- The tank should have lots and lots of hiding places.
In a paludarium setup, it is possible to keep dwarf shrimp and fish with them. Marble crabs do not show any interest in going into the water.
Bad Tank Mates:
- Any Crayfish species.
- Other crab species.
In Conclusion
Marble crabs are very cool, but just like any other pet, they have special needs that their owners need to know about because it is very unlikely that you will be able to add these animals to a pre-existing tank.
However, it should not scare you. These crabs are about as low-maintenance as it gets. So, setting up a 5 or 10-gallon tank will not be too difficult. As long as you have a handle on their main care requirements there should not be any trouble keeping them as pets.
Marble crabs are a great option for someone looking for a change from fishkeeping.