Watermelon fiddler crab, widely known as watermelon crab, is a fascinating species of fiddler crab that has a huge defensive armor (claw) which is half of their size. Although this is quite an old species, it is not so popular among hobbyists, and finding guides about them is more difficult.
Here I’ll talk about everything you need to know about the watermelon fiddler crabs, including how to care for them and related facts.
A quick overview of the watermelon fiddler crab
| Names | Watermelon crab, Watermelon fiddler crab, Mangrove fiddler crab, thick-legged fiddler crab, Scarlet fiddler crab |
| Scientific name | Paraleptuca crassipes / Uca crassipes 1 |
| Care level | Easy |
| Size | 3.4cm |
| Deit | Omnivore |
| Lifespan | Up to 3 years |
| Sleeping nature | Nocturnal |
| Temperament | Peaceful |
| Habitat type | Brackish paludarium |
| Optimal temperature | 75-85°F (24-29°C) |
| Color | Pale, dark blue, and orange |
Habitat and distribution
They live in intertidal mangrove forests, especially near shore and are widespread throughout Western Pacific and Southeast Asia—Japan, the Philippines, Thailand, Indonesia, and China.
Some facts about watermelon fiddler crabs
Appearance
The coloration of their bodies resembles the watermelon skin, where they get their name from. There could be a few large, pale / sky blue blotches on the dark blue carapace, along with dark orange to light orange claws and legs.
The carapace can reach approximately 1.3 cm in length and 2 cm in width, with the larger claw reaching up to 3.4 cm.
Armour
Like the other fiddler crabs, the watermelon crab uses its larger claw to fight and to warn other males to stay away from its territory. Sometimes it prevents unnecessary, harmful conflict.
If the crab loses its claw, it can fully regenerate the claw after a molt. The irony lies in the fact that, following molting, the male’s larger, lost claw will grow from the opposite side.
The males have one big claw and the females have two small claws—an easy way to differentiate between male and female.
Burrowing
Each crab has its own burrow; its purpose is to be safe from predators during the day while the crab is sleeping, as well as a water source and a mating place.
How to care for watermelon fiddler crab
Setting up their habitat
They will need a paludarium to thrive where they have access to water, along with enough surface area where they can burrow sand, walk, climb and do other stuff.
Paludarium is because the watermelon crabs have modified gills that need air to breathe, but the gills always have to be moistened to work perfectly and they also can’t stay for long as they can drown.
Tank size
The watermelon crabs are very tiny and social. That’s why you can keep them as a small group of 5 to 10 crabs in a 10 gallon tank. If you keep them with other crabs and animals, choose a minimum 20 gallon tank.
Suitable substrate
Choose a sand substrate, prefer beach sand and mix it with small gravels and soil; it will replicate their wild substrate, which will help them with burrowing.
Pour the substrate into at least 4 inches of the tank. Start a slope from one side to the other side. The lowest sand level should be 1 to 2 inches deep and the highest level should be 4-5 inches.
You can also do it with a plastic box or something like that to keep a section for water.
Water
Prepare the brackish water with reef salt and pour it in the tank. The water should not be too deep; basically, the depth of the water should be as deep as the biggest crab so that the crab can fully submerge without getting drowned and can easily get out of the water.
The brackish water and the paludarium are necessary because they are semi terrestrial and live in areas where they get a mix of saltwater and freshwater. Only freshwater will end up killing them; maintain a salinity level of 1.000 to 1.015.
Decoration
Keep several climbing mediums; they can be rock or plastic pipe. Using wood such as half log pipe, cholla wood and spiderwood can be a good option.
Can you keep plants in the watermelon crabs’ tank? My suggestion is no. Plants are good for creating a natural environment but the problem is that the roots of the plants spread over time, which can block the way of their burrowing.
It is just a problem that is faced by many owners but you can always consider plants in the tank as long as the roots are not blocking the way.
Temperature, Humidity and Light
Keep the temperature between 75 and 85°F (24 and 29°C), which is a typical temperature for a paludarium. Keep an eye on it using a thermometer, ensuring it doesn’t fluctuate much.
The enclosure should always have a humidity level between 70% and 80%. Track the humidity with a hygrometer and consider using a humidifier or a mister if necessary.
Watermelon crabs won’t need sunlight if they get aquarium lights that mimic the natural day and night.
Molting
They shed their exoskeleton through molting as they get bigger over time. They may eat more and spend more time burrowing during the process. If you see molting signs in a crab, ensure no one disturbs it, as they are vulnerable and weak at this stage. You can keep one in isolation if necessary.
Diet for watermelon crabs
You should not worry about what watermelon crabs can eat or not. You can give them literally everything, since they are omnivorous.
In the wild, they depend on plant matters, decaying organisms, algae, etc. In captivity, you can give them fish food, turtle food, flakes and pallets.
Complement the diet with vegetables and fruits, as well as bloodworms, brine shrimp, frozen food and other seafood.
