Geosesarma hagen (also known as Red Devil Crab) is one of the most colorful and interesting pets in the crustacean world. These little semi-terrestrial crabs have a lot of personalities and are a load of fun to watch.
Red Devil crabs make amazing pets. They are gorgeous, relatively easy to care for, low maintenance, and can be bred in captivity. A properly set up paludarium can become the focal point of any living room.
If you consider keeping Geosesarma hagen as pets, there are a few important tips that you need to know about this species. Therefore, in this article, you will find information on how to care for Red Devil crabs, their feeding preferences, optimal setup, etc.
Quick Notes about Red Devil Crab
|Name||Red Devil Crab|
||Red Vampire Crab|
|Scientific Name||Geosesarma hagen|
|Tank size (minimum)||5 gallons (~20 liters)|
|Size of the carapace||up to 2.5 cm (1 inch)|
|Size across the leg span||up to 5 – 7 cm (2 – 3 inches)|
|Optimal Temperature||24 – 28°C (~75 – 82°F)|
|Aquarium type||Paludarium (aquarium that has both terrestrial and aquatic elements (freshwater)|
||75% and higher|
|Nitrate||Less than 20 ppm|
|Life span||up to 2 years|
|Color Form||Orange or red with yellow eyes|
Why are They Called Red Devil Crab?
Geosesarma Hagen species got its name after the Rolf C. Hagen Group of Companies, a major pet supplies company in Germany, who kindly supported the study in Java.
They also got their common name “Red Devil crabs” as a good marketing move and as a part of the theme. For instance, Geosesarma Dennerle (Vampire crab) and Geosesarma Hagen share the same natural habitat.
Catchy names always attract buyer’s attention and also helps in self-promotion.
Natural Habitat of Red Devil Crab
There is no much information regarding their natural distribution. So far, these crabs are endemic to the island from Central Java, Indonesia.
Geosesarma Hagen species lives in forests (between rocks and among the dense vegetation) near freshwater rivers and lakes. They do not depend on saltwater for development.
Description of Red Devil Crab
The most interesting thing about Red Devil Crabs is, without a doubt, their appearance. These crabs are really fascinating!
Like all crabs, they have a total of ten legs including two pinchers which they use for eating. The claws are small and do not open very wide.
The carapace of an adult Red Devil crab can grow to about 2.5 cm (or 1 inch) long, with a leg span of up to 2-3 inches (5 – 7 cm).
Distinguishing characteristics of Red Devil crab:
- Squarish body, slightly wider than long.
- The dark brown coloration on the anterior part of the carapace and walking legs.
- The posterior part of the carapace is orange or reddish.
- The abdomen is greyish.
- Eyes bright yellow.
- Claws are orange or reddish.
In nature, the coloration of hatchlings is almost dark while young Red Devil Crabs is generally more reddish than orange.
Lifespan/Longevity of Red Devil Crab
Under optimal conditions, Red Devil Crab can live up to 2 years. However, the average lifespan is around 1.5 years.
Obviously, their life expectancy depends on a number of factors such as disease, poor living conditions, and shipment stress!
Unfortunately, because of poor care when Red Devil Crabs were captured and brought to the big brand pet stores, they may die soon after purchase. As a result, some hobbyists believe that this species is not beginner-friendly.
Actually, it is not completely true.
Once settled and acclimatized to a new environment Geosesarma hagen (Red Devil Crabs) becomes pretty hardy and easy to care for.
Behavior of Red Devil Crab
As surprising as it may sound, Red Devil crabs are hunters! Wood lices, worms, fruit flies, and other live foods are really their preference.
Red Devil Crabs are nocturnal and will spend most of their days hidden from the light in order to avoid being seen. It is at night when they truly come alive, roaming around the tank both on land and underwater looking for food or a new hiding spot.
Once settled, their behavior will become more outgoing and they will come out more often even during the daytime.
Red Devil Crabs are also pretty active and social. They prefer the company of their species members. It makes their life richer and less stressful.
Larger colonies often have more active members, which can be seen venturing out from hiding and showing off more often.
Although Red Devil Crabs are not territorial and aggressive, like most crab species, there can be some fights between them from time to time. That is why hiding places are so important in crabitats.
Red Devil Crabs are not diggers in their true sense, but they can push out some soil to make their own dens. In nature, they usually do that at the edge of the water bodies.
- Social: Yes
- Active: Yes
- Peaceful: Yes (generally)
- Burrowers: No (generally)
Feeding Red Devil Crab
Although in captivity, these crabs can eat detritus and dead plant parts, they are not vegetarians. On the contrary, according to the studies, these crabs seem to be more carnivorous, feeding at least partially on insects inhabiting the ground.
Red Devil Crabs will accept a variety of foods but are much more vigorous and enthusiastic when hunting live prey (wood lices, worms, fruit flies, small crickets, bugs, etc.).
Foods Red Apple 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, etc.)
- Frozen blood worms.
- Detritus worms.
- Brine shrimp.
However, the mere fact that these crabs are not picky eaters does not mean that you can give them the same food every day. Do not do that, it can make them sick and shorten their lifespan.
Red Devil Crabs need a well-balanced diet:
- Protein (the main)
- Vegetables and Fruits
Therefore, you can also give them:
- Vegetables (like broccoli, cabbages, carrots, cucumbers, lettuce, corn, spinach, peas, squash, leafy greens, etc.).
- Fruits (Apple, banana, pear, melon, mango, etc.).
As for calcium, it is a crucial component of Red Devil Crab’s shell, cellular function, and overall health.
A calcium deficiency can cause weakness and crack in the shell of your beloved pet, and when this happens, the crab becomes susceptible to diseases, heat, and dehydration.
Calcium can be found in such products as:
- wonder shells,
- oyster shells,
- insects, etc.
Note: A few small pieces of cuttlefish bone should be in the tank all the time if you want to keep Red Devil Crabs strong and happy.
- Diet Type: Mostly carnivore/omnivore
- Food Preference: Meat
- Feeding Frequency: 3 – 4 times a week
How Often to Feed Red Devil Crab?
Adults can be fed 3 – 4 times a week whereas juveniles Red Devil crabs should be fed daily.
However, the most important rule is that you should not let the Red Devil crabs starve. Otherwise, despite their relatively peaceful temper, they can even cannibalize.
How often should we change the food for Red Devil Crab?
Generally, we can leave their food for 24 hours before removing it to prevent moles.
Also, it is best to feed them at night or in the evening because they are nocturnal animals who naturally eat when others sleep. In addition, by doing so you’re recreating natural conditions for your Red Devil crabs.
How to improve Red Devil Crab coloration?
As with shrimp, we can also enhance their coloration by adding astaxanthin to their diet. You will see a big difference.
You can also read “How to Enhance Shrimp Color?” (the principle is the same with Red Devil crabs).
Are Red Devil Crabs Plant Safe?
Yes, Red Devil crabs are plant safe. They are mostly carnivorous and do not eat live plants. They also usually do not uproot or cut plants.
Keeping and Caring for Red Devil Crab
First of all, I need to repeat it once again, Red Devil crabs (Geosesarma hagen) are not full aquatic animals. Depending on their age their water requirements differ.
For example, a 5-gallon (20 liters) tank with lots of hiding places can easily house 3 Red Devil crabs (1 male and 2 females).
In some articles, you may see that the minimum size is 10 gallons (40 liters) or even more.
Well, on the one hand, the bigger the tank, the better it may be to setup a paludarium with diverse areas for them to dwell. On the other hand, if we are talking about minimum but acceptable requirements, I completely disagree with it.
It is all about hiding places! In a 10 gallon tank, you will rarely see these small crabs unless you decide to keep at least 7-8 crabs in it.
Note: Red Devil crabs are great escape artists. So, a tight-fitting lid is essential.
Land vs Water Ratio:
Red Devil crabs are not aquatic; they are semi-terrestrial crabs. Ideally, the land area should take at least 70% of the space in your tank or even more.
For example, in nature, adult crabs are not found in the water very often. They mostly live on the moist banks. However, juvenile crabs are often in the water or very close to the waterline. They are not frequently seen on the drier forest ground.
There are several reasons for that:
- Young crabs molt frequently. To do so they need water.
- Water provides more hiding places and, generally, is a safer place.
Water Bowl and Water Type:
Red Devil crabs do not need a lot of water.
Therefore, instead of creating a complex tank setup with filters, you can use a simple water bowl. However, there are some important rules here:
- The bowl should be deep enough to completely submerge your crabs. As long as water pools can completely cover their entire bodies, they will be fine. Therefore, 2-3 inches (5 – 7 cm) will be deep enough.
- It should be big enough to fit at least half of your crabs in it at the same time.
- It also should have some hiding places. Remember, Red Devil crabs molt in the water.
For example, let’s say you have 5 adult Red Devil crabs. Your bowl should fit at least 3 of them simultaneously, meaning 3*2 (size of the crab) = 6 inches. So, the water bowl should be at least 6×6 inches or (15x 15 cm).
Important: Red Devil crabs cannot stay in the water all the time. They will drown. It is crucial to provide a variety of surfaces for them to get out of the water.
Red Devil crabs need only freshwater!
If you use tap water, add Seachem Prime (link to check the price on Amazon) to remove chlorine, chloramine. This water conditioner will also bind to heavy metals, any ammonia, nitrites, or nitrates present for up to 48 hours. Consider Prime as your additional safety net.
If you are using RO/DI systems, you will have to remineralize the water with Salty Shrimp GH/KH+ or GH+ (Read more about it here).
Pros and Cons of Water Bowls
- All water changes will be very easy and simple.
- There will be no need to use any filters to maintain cleanliness and prevent toxicity!
- Water bowls usually do not look great in the setup unless you know how to decorate and hide things.
- Frequent water changes. You will have to replace it every 2-3 days.
Classic Paludarium Setup
If you do not want to use a water bowl and decide to go for a classic paludarium setup for Red Devil crabs, you need to know their preferences. These crabs thrive in water with:
pH: a pH range of at least 7.0 – 8.0. If the pH is too low, they may become lethargic.
Temperature: temperature should be around 24 – 28 C (75 – 82 F).
Hardness: KH 0 – 10 and GH 4 – 16.
To replicate their natural environment, provide Red Devil crabs with coconut fiber, soil, and peat.
There is no need for a very deep substrate. In most cases, 3-4 inches (7-10 cm) will be enough.
Substrate plays an important role in Red Devil crab setups:
- Hiding places. Let’s them excavate their own dens.
- Humidity. Helps to maintain humidity in the tank.
The substrate should always be kept moist and have a ‘sandcastle’ consistency. It means that it should hold its shape when you squeeze it. However, not so wet that it drips or pools water.
How do you know that you have ‘sandcastle’ consistency?
- Take a pencil.
- Stick it all the way down the substrate and pull back up.
- The tunnel should not collapse.
Red Devil crabs enjoy a warm and humid environment, the range of optimal temperatures is anywhere between 24 – 28°C (~75°F – 82°F).
Crabs are “cold-blooded” animals, in other words, their body temperature completely depends on the temperature in their surrounding environment.
Their metabolism (activity) slows down when the body temperature drops. If it drops too low or too fast it can cause a temperature shock.
To prevent this, it can be a good idea to have a heat mat under the tank to keep the tank warm.
Humidity levels are very important. Red Devil crabs need moist, and humid air to breathe. The humidity level should be more than 70%. In ideal range would be between 75 and 90%.
How to control humidity in the tank:
Humidity can be changed 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: Red Devil crabs need stability and high humidity. This is one of the reasons why people fail to keep them.
No special requirements. Red Devil crabs are nocturnal animals.
If you have plants, lighting should be adapted to their needs. In all other cases, you may not even need one.
Decorations and Hiding Spots:
Red Devil crabs need a lot of hiding places to be happy. A LOT! Seriously, it is absolutely crucial to minimize stress to your crabs by giving them a lot of places to hide, even in water!
The more hiding places you have the more active they become. No, it does not sound strange.
The point is that when they do not have enough hiding places they feel less secure. As a result, they are more likely to spend more time hiding.
Live plants, PVC pipes, pieces of bark, driftwood, wood, stones, nets, porous bricks, and other decorations will enrich the environment and provide shelter and hiding places.
Tip: Give the moss, they like to sit and hide in it.
Basic Tank Setup for Red Devil Crabs (links to check the price on Amazon)
Red Devil Crab and Molting Cycle
In order to grow, Red Devil crab will shed its exoskeleton (exoskeleton) in a process called molting. It also allows them to restore lost limbs.
This process consists of 4 phases:
So, your crabs are about to molt. This can be a bit stressful for them, so you should follow these guidelines:
- NEVER disturb your Red Devil crabs when they’re molting.
- Give it time – this is the most stressed moment in their life
- Keep giving calcium-rich foods and food that has minerals. It will allow the crab to harden the shell faster.
- Don’t remove old exoskeletons from the tank because there are lots of nutrients left inside it. Red Devil crabs will eat it later.
- Just keep putting new food in the tank even if they’ve been missing for days at a time
- Don’t panic if they do not come up after molting for a few days. They hide during molting.
Rules: How to Care and Handle Red Devil Crabs:
- Red Devil crabs are not pets you can play with. Do not take them out just because you want to.
- Red 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. Keep in mind, Red Devil crabs can store uneaten food in their burrows.
- Provide as many hiding places as you can!
- Keep the warm temperature and high humidity.
- The substrate should be based on coconut fiber, soil, and peat to give them a homely feeling.
- Make sure the lid of the tank is closed tightly so that they cannot escape it.
As you can see, it is not that difficult and with the proper steps and precautions, you can care for Red Devil crabs pretty easily.
Sexing Red Devil Crabs
- Abdomens. You can differentiate the gender by the shape of their abdomens. Males have a narrow and slimmer plate while females have a broad plate on their belly.
Of course, females might also be carrying around some fertilized eggs. This is another obvious giveaway when sexing Red Devil crabs.
- Claws. Males have larger and sometimes brighter claws. Females have smaller (about half that size) claws.
Note: Some people, say that males are slightly larger than females. In my opinion, the size of the Red Devil crabs cannot be used as a reliable way to sex them. Unlike most crab species, where males are bigger than females, in genus Geosesarma, it can be really hard to say because of their small size.
Mating Red Devil Crabs
If a female is ready to mate, she will allow a male to approach. After that, the male flips the female upside down and wraps himself around her to fertilize.
Mating usually lasts several minutes.
Breeding Red Devil Crabs
Red Devil crabs start breeding well once old enough and established in the tank.
Although reproductive traits of Geosesarma hagen hasn’t been described in the scientific literature (at least I could not find any at the moment of writing this guide), there are still some reports of successful breeding them in captivity.
According to them:
- Red Devil crabs do not require saltwater to breed. Females release their eggs in freshwater.
- The size of the females positively correlates to their body size and number of eggs.
- Each female can carry a few dozens of eggs.
- Depending on the temperature, incubation lasts 30-50 days.
- Before hatching, females become more secretive and hides almost all the time.
- They have large eggs and direct development (no larval stages). After hatching, females release tiny copies (1-2 mm or 0.04-0.08 inches) of the adults.
- Young Red Devil crabs do not have any orange or red coloration. They are completely dark.
- Young Red Devil crabs also spend most of their time in the water. They seem to use water for protection more than the older ones.
- Small ones should be fed every day. They need the same food as adults. Just crush the pellets between your fingers.
Although adult Red Devil crabs usually do not cannibalize young, if they are not hungry, it is still not recommended to keep them in the same tank.
The problem though is that they are so tiny and secretive that most of the time people cannot even find them until they grow bigger. The only solution, I can think of, is moving a berried female in a rearing tank.
Red Devil Crabs and Suitable Tank Mates
The ideal situation for Red Devil crabs is a species tank. Multiple crabs should be kept in groups of one male with multiple females.
Although Geosesarma hagen is probably one of the most social crabs in the genus Geosesarma, to keep them in large groups, you need to follow several conditions:
- They will compete with each other for food. It can also affect their behavior (aggression). To mitigate this possibility, it is important to make sure that they are well fed at all times.
- The tank should have lots and lots of hiding places.
In a paludarium setup, it is possible to keep dwarf shrimp and small fish with them. Adult Red Devil crabs do not spend a lot of time in the water in any case.
Bad Tank Mates:
- Larger or aggressive fish.
- Any Crayfish species.
- Other crab species.
- Dwarf frogs.
Yes, but I would not recommend it. Some species, for example, Vampire crab, can be more aggressive, some species can be smaller. It can all cause conflicts.
When it comes to coloration, Red Devil crabs are one of the coolest creatures in our hobby.
These semi-terrestrial crabs are easy to care for once you understand their needs and preferences. Therefore, you should only acquire these crabs if you are willing to give them special care and attention.
Let me know if you have any questions that I did not cover in this guide. I am more than happy to help, and love hearing from my readers!