Fiddler Crab: Species Profile

Characteristics, Housing, Diet, and Other Information

Male fiddler crab on wet sand
David Wong / Getty Images

The term "fiddler crab" refers to about 100 species and subspecies of crabs from the genus Uca. They’re found along beaches and brackish (a mixture of saltwater and freshwater) waterways around the world. Male and female fiddler crabs are easily distinguished by looking at their claws. The females have small claws while the males have one distinctive large claw. This large claw, held in such a way that it resembles a fiddle (violin), is how fiddler crabs got their name. Fiddler crabs are fun to watch and fairly easy to keep as pets, with few health concerns and docile personalities. Their housing takes up minimal space, and there are many commercial foods available to provide them with a balanced diet.

Species Overview

Common Name: Fiddler crab

Scientific Name: Uca minar

Adult Size: About 2 inches long

Life Expectancy: Up to 3 years in captivity

Fiddler Crab Behavior and Temperament

Unlike land hermit crabs, fiddler crabs spend a lot of their time in water. In the wild, they retreat to muddy burrows as the ocean tide goes out. In addition to digging burrows, picking up food, and defending themselves, fiddler crabs also use their claws to communicate. They will raise and lower their claws like a wave, which alerts other crabs to their presence. 

In general, fiddler crabs are calm and quiet creatures that rarely display aggression. They can be kept with other crabs of their species, but you must watch out for males fighting over territory or a female in the tank. If this occurs, they’ll need to be in separate tanks. In addition, it’s best not to keep fiddler crabs in a tank with fish or any other species; they might try to catch the fish for food.

Fiddler crabs should be handled as little as possible, as this can cause them undue stress. Plus, they might pinch you with their claws if you frighten them. Instead, simply enjoy watching them as they move about their tank. And expect to spend just a few hours per week on feedings and keeping the tank clean.

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Housing the Fiddler Crab

Provide at least a 10-gallon aquarium if you have one to four fiddler crabs. Add 3 to 5 more gallons of tank space per each additional crab. Overcrowding is a major source of stress for crabs, and it can lead to health problems and aggression. Make sure the tank has a secure lid with ventilation (such as a mesh screen), as fiddler crabs can climb out of their tank when given the chance.

To mimic their natural habitat, fiddler crabs in captivity need brackish water and a dry land area in their aquarium. You can create this by sloping sand down from one side of the tank to the other. Then, fill the tank so that water covers roughly half the sand. The water only needs to be a few inches deep. You also can place some large rocks in the water to create small islands that the crab can climb onto. Plus, you can add some plastic or live aquarium plants, pieces of driftwood, and other decorations to enrich the environment.

Use an aquarium water conditioner (available at most pet stores) to remove chlorine from the water. And then add aquarium salt to replicate the brackish conditions. Your package of aquarium salt might have instructions on how to create brackish water. The general rule for fiddler crabs is to add enough salt to the water to attain a specific gravity (a measurement for liquids that determines whether an object will sink or float in them) between 1.005 and 1.01. The specific gravity can be measured with a hydrometer, which is found at many pet stores in the fish section.

Furthermore, use a thermometer to ensure that the tank temperature is between 75 and 85 degrees Fahrenheit. If you need supplemental heat, position a reptile heat lamp over the land area of the tank.

A filter for the tank is optional, but it will keep the water clean for longer. Only use an internal tank filter, as fiddler crabs have been known to climb up external filter tubes and escape. If you don’t have a filter, plan to change around 20% of the water every few days. If you have a filter, you’ll likely only have to do this every one to three weeks, depending on how many crabs are in the tank creating waste.

Food and Water

In the wild, fiddler crabs are scavengers that eat bits of organic matter they find in the sand and mud. In captivity, there are formulated commercial diets especially for crabs that make their feedings a breeze. You can find these foods at most pet stores that sell fish and crabs. In general, they are nutritionally complete flakes or pellets that you simply drop in the water where your crab will scavenge for them. You can also supplement their diet with several foods, including brine shrimp, blood worms, plankton, seaweed, and zucchini. 

Follow any package instructions, as well as your veterinarian's advice, for how much and how often to feed. Feeding at the same time each day isn't critical, but you should remove uneaten food within 24 hours to prevent it from dirtying the water. Fiddler crabs do not need any supplemental drinking water.

Fiddler crabs as pets illustration
Nusha A. / The Spruce

Common Health Problems

Fiddler crabs generally don't display many health problems, though one sign of overall poor health is a loss of legs or claws. Most commonly, any issues are due to incorrect water conditions, poor tank cleanliness, or a nutritional deficiency. If you notice your crab is sluggish or not eating, check the tank conditions. And consult your veterinarian to make sure you're feeding the proper diet.

Fiddler crabs go through regular molting—that is, shedding their exoskeleton and forming a new one. Prior to a molt a crab might slow down and lose its appetite, and during a molt it can appear fairly lifeless. This is normal. Do not disturb a crab during this molting process, which can take weeks to complete. Crabs are extremely fragile during this time, as their new exoskeleton must harden before it becomes protective. Also, wait about a week to remove the old exoskeleton from the tank, as your crab might ingest part of it for extra calcium. Fiddler crabs also can regenerate any lost legs or claws when they molt.

Furthermore, female fiddler crabs might produce eggs in captivity. But odds are you won't have baby crabs. Successful rearing of young fiddler crabs in an aquarium is next to impossible. In the wild, the larvae of fiddler crabs grow in deep ocean waters and return to shore at maturity. Because aquariums aren't deep enough to mimic this, the crab life cycle is rarely successfully completed in captivity.

Purchasing Your Fiddler Crab

Fiddler crabs are legal to keep in most areas, though some landlords might have rules about these animals as pets. Unfortunately, many pet stores keep fiddler crabs in a freshwater aquatic setup, even referring to them as freshwater crabs and then recommending the same setup to new owners. Fiddler crabs might do fine housed in freshwater for a few weeks, but eventually, they will become weak and die if they don't get a tank with brackish water.

So when you're looking for a pet crab, aim to purchase from a breeder, pet shop, or rescue group that keeps its animals in the appropriate brackish water from the start. That way you're more likely to get a healthy animal. Make sure the seller can give you information on the crab's origin, age, and health. And be sure to choose a crab that isn't missing any legs or claws, as this can indicate trauma or poor health. Expect to pay around $5 to $10 on average.

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