Halloween Moon Crabs (Gecarcinus quadratus) or Moon Crabs are lovely creatures and amazing pets for keepers of any level. These crabs have perky personalities and make movements that are interesting to watch.
Halloween Moon Crabs are terrestrial carbs that require high temperature and humidity to feel comfortable. Although Halloween Moon Crabs are very easy to care for, they still require a bit more care than you may have been led to believe in pet stores.
In this care guide, I discuss everything you need to know about Gecarcinus quadratus species including their behavior, life span, growth, feeding, handling, embryonic development, and much more.
Quick Notes about Halloween Moon Crab
| Name | Halloween Moon Crab |
| Other Names |
Moon Crab, Purple Moon Crab, Harlequin Crab, Harlequin Land Crab, and White Spot Crab |
| Scientific Name | Gecarcinus quadratus |
| Tank size (minimum) | 15 gallons (~60 liters) |
| Keeping | Easy-Medium |
| Breeding | Very Difficult |
| Size (carapace) | up to 2-2,5 inches (5 – 6 cm) |
| Optimal Temperature | 26 – 29°C (~79°F – 88°F) |
| Water type | Freshwater and saltwater bowls |
| Moisture | at least 80% |
| Substrate | more than 6 inches (15 cm) |
| Diet | Mostly herbivore/omnivore |
| Temperament | Aggressive |
| Life span | up to 8 years |
| Color Form | Purple, black, and orange |
Origins, Natural Habitat of the Halloween Moon Crab
Halloween Moon Crab is a tropical terrestrial crab that was initially described by de Saussure in 1853.
This species has a general distribution along the Atlantic and Pacific coasts of tropical North, Central, and South America. They can be found in coastal forests along both the Atlantic (Florida to Guyana in northeastern South America) and Pacific (Mexico to Peru) coasts of the Americas.
Within Costa Rica, they have a general distribution along the northern Pacific coast at Bahía de Culebra, Cabo Blanco, Puntarenas, Boca de Barranca, Caldera, and Pigres and along the southern Pacific coast at Golfito.
Halloween Moon Crabs live high above the tide line and often at a considerable distance (generally up to 600 m or 7 yd.) from any water.
Note: Halloween Moon Crab may be synonymous with Gecarcinus Lateralis.
Description of the Halloween Moon Crab
Halloween Moon Crabs get their name because they look like they are dressed for Halloween. They have all the Halloween colors – purple, black, and orange. These guys look really gorgeous with a dark carapace, orange-red legs, and purple-blue claws that become white closer to the tips.
In addition, they have two small white spots on the back of their carapace and orange spots behind the eyestalks.
As they age their colors will become lighter and more washed out. The same happens when they are about to molt, the carapace usually loses its brightness. This is absolutely normal and it should not worry you. After molting their colors will be more vivid.
Halloween Moon Crabs do not grow big. The carapace of an adult crab only grows to about 2 – 2,5 inches long (about 5 – 6 cm), with a leg span of up to 4 inches (about 10 cm).
Note: There are reports that in the wild some individuals can measure up to 4 inches or 10 cm (carapace size). However, this is very rare.
Halloween Moon Crabs have a gill chamber (not lung). The gill chamber is located under the carapace near the first pair of walking legs. As long as their gills stay moist, they can be out of the water.
Difference between Rainbow Crab and Halloween Moon Crab
Even though crabs are a somewhat unorthodox pet, more and more hobbyists are giving crab keeping a try. The problem is that there are so many crab species in the world, that pet stores can easily confuse some of them.
Mistaken Identities is one of the main reason, why people cannot provide proper care for these crabs.
| Rainbow Crab (Cardisoma Armatum) | Blackback Land Crab (Grecarcinus Lateralis) | Halloween Moon Crabs
Gecarcinus Quadratus |
|
| Vivarium type | Paludarium | Terrarium | Terrarium |
| Size of the carapace | Up to 4 inches | 2 – 2,5 inches | 2 – 2,5 inches |
| Color form | Purple-blue carapace. Whitish claws.No dots on the back.White to grey eyestalks. |
Mostly reddish with a dark spot on the back. Usually do not have dots on the back. Dark eyestalks. |
Mostly orange legs with a fully dark carapace.
2 white and orange dots on the back and near eyes. Dark eyestalks. |
| Temperament | Very aggressive | Aggressive | Aggressive |
Related articles:
- Rainbow Crab – Detailed Guide: Care, Diet, and Breeding
- Blackback land crab – Detailed Guide: Care, Diet, and Breeding
Lifespan of Halloween Moon Crab
Most articles and care sheets on the Halloween Moon Crabs mention that they live for about 10 years. I have tried to find proof for that but I couldn’t.
Therefore, I started asking other people who kept or still keeping Halloween Moon Crabs as pets.
After summarizing the results, I have to say that, under optimal conditions, the average lifespan for the Halloween Moon Crabs is 4 – 8 years or so in captivity.
So far I do not know a single case where somebody managed to keep them longer. Maybe they tend to live longer in the wild if they don’t fall prey to any other species.
Behavior of the Halloween Moon Crab
Halloween Moon Crabs are very shy and skittish creatures. They do not like to be touched or handled in any way.
They are nocturnal and spend most of their time hiding. However, if you do see them exploring the tank, they will most often always be scavenging for food.
Keep in mind that they are excellent climbers and escape artists.
While Halloween Moon Crabs are considered relatively easy to care for. It is important to remember that they have a semi-aggressive temperament, a characteristic that may turn off some potential owners.
Generally speaking, aggression in Halloween Moon Crabs is latent until they grow into their adult size. At this point, they may become more aggressive (especially males) and will likely attack other tank mates.
Halloween Moon Crabs are not social; on the contrary, they are solitary and territorial creatures. They will pinch and claw when they feel threatened.
Like many crab species, Halloween Moon Crabs are efficient diggers. It really does not matter how many places to have you can provide them, they will dig. They love digging!
According to the studies, their burrow chambers can extend from 15 to 150 cm (6 inches to 5 ft.) deep! However, in most cases, the distribution of burrow depths ranged from 30 – 70 cm (12 – 28 inches) depth,
Note: They can spend days and weeks in their burrows. So, do not panic if you have not seen it lately. Also, DO NOT try to dig it out! It stresses them a lot!
Halloween Moon Crabs are very messy and destructive. They will constantly move stuff and “redecorate” your tank to their liking.
Halloween Moon Crab and Strange Sounds
Interesting fact: During the investigation of the defensive adaptations of some crabs, Researchers discovered that Gecarcinus quadratus can produce 2 types of sounds when disturbed in their burrows and also at night.
- The first is caused by friction of the claws against the carapace.
- The second type of sound is a bubbling sound caused by fluid being forced out of their mouths. This occurred whenever the crab was grasped. The fluid was brown in color and had a bitter taste that is possibly unpleasant to a predator.
According to the observations, sound production also preceded attack autotomy and occurred when the crabs were attacked with a dummy predator.
Scientists believe that the sound can have a startling effect that could temporarily disorient an attacking predator or if the sound were produced in close temporal proximity with pain inflicted by claws the predator might learn to associate the sound with the pain and exhibit avoidance behavior in the future.
Feeding Halloween Moon Crab
Halloween Moon Crabs are extremely opportunistic eaters. It means that they can eat about anything edible they come across.
Unfortunately, this is another beginner’s trap. People often think that if their crabs eat some products, so they can give more and more of them. Wrong!
If we want to keep our crabs healthy, we have to know what they eat in the wild.
In their natural habitat, they lean more towards the herbivore side like leaf litter, fruits, seeds, seedlings, the detritus of decomposing plants, and benthic algae they find in the sand along the shoreline.
In captivity, Halloween Moon Crabs enjoy a varied diet and will readily eat just about anything they are offered including some bits of organic matter.
Important: Despite your crab’s food desires, you should avoid giving protein-rich foods (such as cricket, bloodworms, live brine shrimp, etc.) all the time. It should be given only as a treat or in addition to other food for extra nutrients.
Personally, I would say that their diet should be:
- at least 90% herbivore (fruits, berries, flowers, leaves, plants, vegetables, etc.)
- less than 10% protein.
Be very careful with that. For example, under high humidity, protein food gets moist and soggy very fast. As a result, it will mold and mold kills crabs!
Related article:
How often should We Change the Food?
You can leave their food for 24 hours before removing it. Just make sure that whatever they do not consume in one day is removed to prevent moles.
Keep in mind that Halloween Moon Crabs are nocturnal. So it is recommended to feed them at night (at least in the evening) so that you can replicate the conditions and environment under which they eat naturally.
How often should We Change the Menu?
Halloween Moon Crabs prefer a wide choice of food (2 – 4 different types). Otherwise, the consumption rate will decrease with every day.
Ideally, you need to swap up (all different types) pretty much weekly.
Do Halloween Moon Crabs Need Calcium?
As with all crustaceans, Calcium is crucial to a Halloween Moon 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.
Cuttlefish bones – link to check the price on Amazon.
Keeping and Housing Halloween Moon Crab
Halloween Moon Crabs are not high-maintenance pets. But if you want to have a happy and healthy crab as long as it is possible, it is important to give it everything it needs, including proper care.
Of course, they can survive some extreme situations. However, there is a big difference between thriving and surviving after all.
Tank Size (Enclosure):
A 15 gallon (60 liters) terrarium with a screen top is recommended minimum for one Halloween Moon Crab.
If you are housing two or more together, at least a 30 gallon (120 liters) terrarium is needed.
The ideal group is all females or one male and one or two females. It is not possible to keep males in the same tank. So, house extra males in separate terrariums to prevent fighting.
Note: Females of this species are less aggressive than males but they can still be aggressive. It is not possible to guarantee peaceful coexistence.
Important: Last, but not least a tight-fitting lid is mandatory! Halloween Moon Crabs will escape if given the opportunity. Cover even the smallest of gaps. You will not believe how good they are at escaping. Once outside the tank, they will die of dehydration within 24 hours.
You can also read “Difference between Aquarium, Terrarium, Riparium, and Paludarium?”.
Substrate and Decorations
The terrarium should have a proper substrate and decorations for the Halloween Moon Crabs so that they can have their individual spaces if there is more than one crab
The option for the substrate is coconut fiber, soil, peat, and sand.
Personally, I find the mix of sand or Coconut Fiber Substrate to be the best option for the Halloween Moon Crab setups. Ideally, it should be topped with a thick layer of moss or leaf litter.
The substrate should be moistened to sand castle consistency at all times.
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, and pieces of bark will do the job. Supply your Halloween Moon crabs with rocks, decorations, plastic balls, plastic tunnels, crab huts, plastic plants, fish netting, and more. These crabs love climbing as well.
Related article:
How Deep should be the Substrate in Halloween Moon Crab Setup?
I will repeat that these crabs are burrowers. In the wild, they can burrow up to 150 cm (6 inches to 5 ft.) deep. Obviously, it is not possible to have such a huge terrarium only for 1 crab.
So, the real question is what is the minimum depth we can provide for Halloween Moon Crabs?
They need at least 15 – 25 cm (6 – 10 inches) of the substrate to feel comfortable.
How often should you change the substrate?
You need to do it every 2 – 4 months.
Substrate options (check the price to Amazon):
Humidity
Humidity levels are really important. Although Halloween Moon Crabs are terrestrial, they need moist, and humid air to breathe properly.
They also need a hiding place that is moist and lovely—this is where they retreat to when it is time to sleep, rest or molt.
Note: Actually, this is the main reason why these crabs dig so deep. In nature, the crab is subject to two predominant seasons: dry and rainy. To avoid desiccation during the dry season, the crabs dig burrows and spend much of their time there. The soil inside crab burrows is damp and humidity is high, so the rate of evaporative loss is low.
Their tank should be tropical in nature with a relative humidity between 80-90%.
So, keep the substrate moist, provide water for your crabs, and use a glass top. If your humidity levels stay too high or too low, it can be remedied by adding more moisture, less ventilation, or by adding more ventilation.
Be careful and avoid over humidifying as a saturated substrate can breed infection. This is normally a trial and error process, so expect it to take some adjusting to get it perfect.
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
Temperature
As Halloween Moon Crabs prefer a warm and humid environment, it is recommended to place a heat mat under the tank to keep the tank warm.
The temperature can be maintained at 73 – 90 degrees Fahrenheit (23 – 32 C). However, the optimal is between 79 – 88F (26 – 29 C).
The heat pad should cover one-third of the tank so that crabs can move from warmer to colder places anytime they want.
Another alternative is to place it on the back outside wall of your glass aquarium. So, in case of malfunctioning, it will not roast your crabs.
I also definitely recommend a thermostat. It will protect your Halloween Moon Crabs from overheating or getting too cold.
Tip: You can always use ceramic or heat bulbs as a heat source. Depending on the setup, it can be even preferable.
One of the most popular heaters – Zoo Med Repti Therm Under Tank Heater (check the price on Amazon).
Water and Food Bowls
Like all living creatures, they need water. In nature, Halloween Moon Crabs live in forests near the ocean. So, you have to provide them with:
- a bowl of freshwater and
- a bowl of saltwater.
It is very easy 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.
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. Tap water will be the last choice.
Tip: When you prepare tap water for the crabs, let it age for a day. The reason behind it is that chlorine evaporates out of water within 24 hours. Next, add Seachem Prime. This water conditioner also removes chlorine, chloramine, bind to heavy metals, any ammonia, nitrites, or nitrates present for up to 48 hours. Consider Prime as your additional safety net.
Depth and Accessibility of the Bowls
The bowls should be easily accessible and large enough for your crabs to climb into them.
Halloween Moon Crabs cannot breathe underwater. So, it is absolutely crucial to provide them some kind of ladder (stones, fake plants, etc.) to get out of the bowls. Otherwise, they can drown.
These crabs do not require deep bowls. They do not like to be submerged. Therefore, 2.5 cm or 1 inch should be enough.
Tip: Halloween Moon Crabs are super messy. As a result of their digging everywhere, they can throw lots of the substrate into the bowls if they are on the same level. Whenever it is possible, place the water bowls higher.
Food bowls are not necessary, but it also makes it easier for you to keep the crabitat clean.
Warning: Do not use sponges in the water dishes. Sometimes people use them to keep the humidity up in the tank and as a ladder. The main problem is that the sponge becomes a source of all kinds of nasty bacteria, which is not good for the crabs.
Some examples of bowls (links to check the price on Amazon):
Lighting
Halloween Moon Crabs are nocturnal creatures. So, they could not care less about it.
Heat lamps are an option. They come in various types, some provide white light that imitates daylight, others provide red, or blue light, also known as invisible light that imitates night time, or only supply heat.
There is no current proof that these crabs require UVB light, although some keepers prefer to provide UVB.
Molting Halloween Moon Crab
The molting process (the molt cycle) is the most important part of crab’s life. Because crabs have an exoskeleton, they must molt (shed the old exoskeleton) in order to grow.
This process has 4 phases:
- inter-molt,
- pre-molt,
- molt,
- post-molt.
These 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. For example, adults molt every few months.
During pre-molting periods, most metabolic activities are reduced to a minimum. They stop eating, burrow, and become very lethargic. They need depth, darkness, moisture, and heat to successfully molt.
It may take a lot of time to prepare for molting. In some cases, it can be weeks!
Therefore, NEVER disturb them when they are about to molt. Even if you have not seen your Halloween Moon Crab for several weeks! Give it time. This is the most stressful moment in its life.
Halloween Moon Crabs 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.
Important: Keep putting and replacing food in the tank! You never know when they can come up from the molt. Give them something that is rich in calcium. They definitely need calcium after the molt. Also, do not remove the old exoskeleton from the tank. It contains lots of minerals and your crab will eat it later.
For more information, read my article “Crabs and Molting Process”.
Some Important Rules Regarding Halloween Moon Crab Care and Handling:
- Halloween Moon Crabs are not pets you can play with. Do not take them out just because you want to.
- Halloween Moon Crabs should never be lifted up by its legs or claws! They can lose a limb by autotomy.
- They can pinch. It is not painful but you can flick your hand instinctively and your crab would go flying. You do not want to have an injured crab.
- 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. Halloween Moon Crabs are shy creatures so provide them maximum hiding spots.
- 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 Halloween Moon Crabs.
- They spend most of their life inside their burrows. So, do not try to take it out. Actually, they are pretty happy in their burrows.
- Make sure the lid of the tank is closed tightly so that they cannot escape it.
Related article:
Halloween Moon Crab – Male and Female Differences
Halloween Moon Crabs are sexually dimorphic. There are a few indicators that give away the gender of the animal.
- Abdomens. Handle them carefully in order to get a look at the underside of the crab. Males have a narrow and slimmer plate while females have a broad plate on their belly.
- Claws. Males also have larger and sometimes brighter claws. Females have smaller (about half that size) claws.
- Coloration and Size. Males have more vivid colors. In many cases, they also have red to orange legs, while females have dull orange legs. In addition, males can be a little bit larger than females.
Note: The last methods are not completely reliable. It is very easy to confuse a young male with a mature female. That is why it is advisable to use it only in combination with others.
Related article:
Breeding Halloween Moon Crab
Halloween Moon Crabs are easy to keep but close to impossible to breed. Currently, the pet industry completely depends on wild-caught species. The problem is that it takes a lot of time for the larvae to develop into a tiny copies of adults and they can do it only in saltwater. They will not develop in freshwater.
The eggs hatch to larvae, which go through several development stages before they convert to tiny versions of adults.
Halloween Moon Crabs must migrate to the ocean to release eggs that hatch into planktonic marine larvae. Although each female may produce many thousands of eggs, only a fraction of them eventually metamorphose and crawl back onto land.
In nature, they release larvae at night, and mostly during ebbing tides. However, they also time their reproduction to coincide with the beginning of the rainy season, presumably so that adults do not dehydrate during their migration to the ocean.
In my research, I have found only one 1 successful case (!) of breeding Halloween Moon Crabs in the laboratory.
- A female with eggs was transferred to the aquarium.
- The water temperature throughout the culturing period was around 28 C (82 F), and the salinity was 31-34 ppt.
- The Halloween Moon Crabs larvae took about 21 days to pass through several stages and metamorphose into the megalopa stage.
- Once the larvae hatched, they feed on brine shrimp nauplii ad libidem.
- Half of the water volume was changed daily to prevent intoxication.
Note: The larvae are strongly attracted to light. This trick can be used during water changes. - An air pump connected to a diffuser provided a gentle current and aeration.
Halloween Moon Crab and Suitable Tankmates
Before putting any new tank mate in with your Halloween Moon Crabs, you should take some things into consideration.
These crabs are not social. It can be risky to house multiple animals in the same tank as well.
Males, in particular, are extremely likely to fight and eventually kill one another when housed together.
Ideally, crabs are usually better in solitary confinement. Multiple Halloween Moon Crabs should be kept in groups of one male with multiple females. However, it does not guarantee that they will not hurt each other during molting!
Do not keep them with Hermit crabs. There will not be peace between them. Halloween Moon Crabs are stronger and can bully Hermit crabs.
Another problem is that Halloween Moon Crabs dig too much. So, it can be very dangerous to any molting crab.
In Conclusion
Halloween Moon Crabs are exotic pets that do not pop up immediately in our minds when it comes to keeping pets.
They are easy to care for once you understand their needs and preferences. Having them as pets can be exciting but it is one big responsibility. After all, they can live for many years.
You cannot pet it like conventional pets but you can share a bond together once you both start to know each other.
Halloween Moon Crabs are cute, unique, and simply amazing! They are very interesting to watch! The only problem is that they like to spend underground most of the time.
References:
- Influence of land crabs Gecarcinus quadratus (Gecarcinidae) on distributions of organic carbon and roots in a Costa Rican rain forest. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 54 (1): 149-161, March 2006.
- Dry season distribution of land crabs, Gecarcinus quadratus (Crustacea: Gecarcinidae), in Corcovado National Park, Costa Rica. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 55 (1): 219-224, March 2007.
- Observations on sound production by two species of crabs from panama (decapoda, Gecarcinidae and Pseudothelphusidae). Crustaceana. 25 (2). 1973.
- Larval Ecology and Synchronous Reproduction of Two Crustacean Species: Semibalanus balanoides in New England, USA, and Gecarcinus quadratus in Veraguas, Panama by Joanna Gyory. 2001.
- Effects of Land Crabs on Leaf Litter Distributions and Accumulations in a Mainland Tropical Rain Forest. Biotropica 35(3): 365-374 2003
- Differential seed and seedling predation by crabs: impacts on tropical coastal forest composition. Oecologia (2004) 141: 661–671. DOI 10.1007/s00442-004-1673-5
You should post a video on this on YouTube. So much misinformation being regurgitated thru trible knowledge such as : they are social and do better in pairs!”
Another trible and often circulated misinformation is the notion that you have to provide a total submerged bath.
And of cause that they should be given meat. Etc etc.
Hi David Salas,
Thank you!
Maybe someday I’ll start a Youtube channel))
Best regards,
Michael
Truly appreciate the detail and research you put into the crabs. With what the pet store said my experience with them would been have been short-lived.
Hi Taun Wakefield,
Thank you 🙂
Unfortunately, they often do not know too much, thus, they can’t provide the necessary information.
I hope that your crab will be healthy and happy 🙂
If you have any questions, you can ask me any time.
Best regards,
Michael
What ratio of salt to water should I add? I can’t find anything about how much to put in his salt water bowl. Please help!!!!
Hi Angelica Christine,
You need to follow the manufacturer’s instructions to avoid mistakes. What sea salt brand do you use?
Personally, I would say that brackish water (on higher end) will be fine. Therefore, you need to have SG between 1.010 – 1.023 (12-33 ppt).
Best regards,
Michael
All this info is really helpful! However I am a bit concerned with the part describing Halloween moon crabs as “aggressive”. They shouldn’t be very aggressive if they are properly socialized.
Hi Hemlock,
Generally, the genus Grecarcinus is not peaceful. It can be really problematic (if possible) to socialize them.
Best regards,
Michael
i really appreciate the advice, im hoping they will breed
Hi Jospeh,
Unfortunately, it is extremely challenging to breed Halloween moon crabs.
Best regards,
Michael
Hi my moon crab got scared when went to take him to clean is enclosure and he pinch me and dropped is claw… is he going to be ok?
He still has one and I read it could grow back but I am not so sure about the information.
Thank you!
Hi Stephanie Bergeron-tremblay,
Do not worry, it will grow back after a few molts.
Check out my articles about that:
– Detailed Guide to Regeneration in Crustaceans
– Crabs and Molting Process
– How to Handle your Pet Crustaceans
Best regards,
Michael