Mud Fiddler Crab (Uca Rapax)

Last updated on July 17th, 2022 at 10:58 am

If you’re someone who has always wanted their own pet crab but doesn’t have the necessary means to care for one, then fiddler crabs are an excellent choice. Not only are they extremely low maintenance, but they’re also adorable and fun to watch!

Fiddler crab, Uca species, are large crabs that can be kept as pets in your home aquarium or terrarium. While fiddler crabs are popular among hobbyists, they can grow to be very large and require lots of tank space and live foods to thrive.

As such, if you’re interested in keeping fiddler crabs as pets, it’s important to be prepared with plenty of supplies and know how to care for your fiddler crab very well before you bring one home.

They are the largest species of crab native to the United States, growing to be over five inches long. They thrive in saltwater environments like estuaries and mudflats and can live up to 20 years in captivity if they’re given the proper care, diet, and habitat.

Here’s how to care for a fiddler crab, with a full species profile to help you determine if it’s right for your aquarium or terrarium.

Origin and descriptions

Fiddler crabs, Uca genus, are sometimes referred to as mud crabs or finger-pointing crabs. These small-to-medium-sized crustaceans are quite common along shorelines in tropical and sub-tropical areas around the world. In their natural habitat, fiddler crabs can be observed using their large front claws to dig burrows into mud banks of coastal estuaries and swamps where they spend most of their time in hiding.

The specific species you’ll encounter as an exotic pet will vary from region to region; some popular examples include Uca lactea (the mangrove fiddler crab), Uca tangeri (Cape Verde Islands black velvet crab), and Uca longipes (Sri Lanka yellow crab). Despite their size, many species are pretty fast—so it’s important not to corner them.

Your best bet is to make sure your crab has plenty of places to retreat from any potential danger. As long as you keep him away from hungry birds and dogs, he should live out his life without too much stress!

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Fiddler crab species profile

Fiddler Crab

The fiddler crab, sometimes known as a river crab or mud crab, is one of two species of terrestrial crabs found in brackish or freshwater. These crabs are equipped with special pincers called chelipeds—one on each side—that they use to dig burrows and catch prey. Their name comes from their ability to snap their claws open quickly.

They can grow up to five inches long and live three to four years in captivity. They’re considered omnivores, meaning they eat both plants and animals; fiddler crabs will eat just about anything they can get their chelipeds on! They tend to be shy creatures who prefer to stay hidden during daytime hours, but once dusk hits, you’ll see them roaming around near puddles and ponds looking for food.

And although most fiddler crabs are easy enough to care for in a home aquarium, there are some conditions that should be monitored closely if you plan on keeping these creatures as pets.

Fiddler crab scientific name

The scientific name of the fiddler crab is Uca rapax

Fiddler crab family

The fiddler crab family is known as Ocypodidae, and there are about 50 different species. This large family includes over 600 different crabs, which can be found living in sand and mud bottoms from Florida all the way up to Canada.


Fiddler crabs are tolerant of most freshwater habitats, but they seem to thrive best in saltwater. You can find them in both marine and brackish environments, as well as mangrove swamps and large puddles that don’t dry out during periods of drought.

They prefer still water (as opposed to flowing) with lots of places to hide—logs or rocks on which they can set up housekeeping, burrows that offer shelter from predators, etc.

Fiddler crabs are native to tropical and subtropical regions around the world. As semi-terrestrial creatures, they require fresh water and land that is several inches deep at all times in order to survive.

Fiddler crab adaptations

Unlike land crabs, fiddler crabs can easily adjust to different salt levels. They use their claws not only for hunting but also for defense, their sharp claws make quick work out of attackers.

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If a predator attacks, fiddler crabs’ claw grabbing reflex makes them even more lethal, by curling up into an armored ball and clasping onto nearby vegetation or each other they stand little chance against their natural foe.

These adaptations help ensure these tiny crustaceans live long enough to enjoy life as an adult. But despite its perilous beginnings, adult life becomes quite comfortable once again when these little creatures reach maturity.

Fiddler crab size

The fiddler crab can grow to about 2-3 inches (5-8 cm) in size

Fiddler crab tank size

Due to their size, the minimum recommended tank size to keep fiddler crab is 10 gallons (38 liters).

Tank requirements

A healthy fiddler crab can live in a small tank with about 10 gallons of water, but make sure that you provide enough space for your crab’s needs. Decorating your pet’s home is as simple as adding large rocks and small pieces of driftwood, which will help create an attractive habitat while giving it nooks and crannies to explore. Sea sponges also make great additions, just be sure not to buy an invasive species!

An under-gravel filter or air pump provides circulation in a smaller tank, and fresh seaweed makes a good treat. You can clean their tanks once every two weeks; simply siphon out any leftover food or shells from under rocks and set up new decorations when needed.

If a crab starts walking sideways (often called crabbing), it might need more room to roam. Giving your pet more floor space by using an aquarium instead of a bowl will solve most problems related to mobility! Other essentials include UVB lighting, heat pads, and thermometers. We recommend buying these items before purchasing a crab so you know what’s required to take care of your pets!

Tank mates

The fiddler crab is solitary by nature, so you’ll need to get your own crab. If you want to give your crab some company, however, look for tank mates that share similar tank needs and biology. The red swamp crayfish (Procambarus clarkii) and large South American dwarf cichlids (Apistogramma) are two good choices that have been known to live harmoniously with fiddlers.

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fiddler crabs are usually not sold as pairs, so you will need to determine whether or not they can be housed together. Male fiddlers reach maturity in a year, while females take two years, but most crab owners keep their crabs separated until they are ready to breed.

If you do wish to pair your crab, be sure he has been with you for at least a month before attempting it—this gives him time enough to adjust and become accustomed to your presence. On average, fiddler crabs lay eggs after three months of maturation; these eggs hatch approximately two weeks later.

Once hatched, separate males from females as soon as possible; they are cannibalistic by nature and too many clutches have been destroyed by aggressive males.

Are they aggressive or peaceful?

The fiddler crab is neither. While they’re naturally territorial and will pinch other crabs, you can keep two or more crabs together as long as you give them plenty of space.

Fiddler crab care

Fiddler Crab

Despite their monstrous appearance, they are extremely easy to care for and make great beginner pets. Their diet is composed primarily of protein and their habitats are usually pretty low-maintenance. However, there are certain guidelines that need to be followed in order to keep your crab healthy and happy.

They are found in coastlines, which means they can survive in any number of environments—but they do require water and a fairly high level of humidity to thrive.

The temperature range for most fiddler crabs ranges from 45°F (7°C) at night, and up to 86°F (30°C) during the day. Given their tropical nature, it’s best to house them outdoors, but if you want to house yours indoors, it’s important to provide a place where they can access warm sunlight; placing them near sunny windows or using ceramic heaters with UV bulbs are common methods.

It’s also important to know that fiddler crabs don’t require much water. A shallow dish of clean, dechlorinated tap water will be sufficient for them. The best way to tell if your crab needs more or less water is by looking at its gills. If they are dark brown or black, it means there isn’t enough humidity and you should either provide your pet with additional moisture or remove some of their current water sources.

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What they eat

Fiddler crabs are omnivores, which means they eat both plant- and animal-based foods. They primarily eat plants like algae and water hyacinths as well as small invertebrates like snails, but will also consume dead fish that fall into their habitat. If your pet fiddler crab refuses to eat its preferred diet of live algae and plants, try switching out its food source or introducing some chopped-up bits of fish or meat.

Fiddler crab lifespan

The average lifespan of this crab in captivity is about 1.5 to 2 years, but it may be longer if they are kept under good conditions. If you want your fiddler crab to live as long as possible, keep it at 70°F with 60-70% humidity. This is especially important for younger crabs that haven’t developed their adult exoskeleton yet, since they will not have matured enough before succumbing to disease or predation.

Why do male fiddler crabs have one big claw?

Fiddler Crab

They use their large claw (or cheliped) during mating season to compete with other males. They’ll face off in competitions, where they clasp their pinchers together and wrestle each other until one can flip his opponent over onto his back.

The crab on top gets access to mates and wins points toward dominance—and at that point, he becomes king of his harem of up to ten female crabs. It also means bigger claws as males grow larger! The size of your male crab’s claw is an indicator of its level of fitness, so if your male isn’t growing or remains small, it could be sick or malnourished.