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Living Organism Care Guide: Fiddler Crabs

Living Care Information

Uca pugilator
Commonly known as fiddler crab,
sand fiddler, calling crab

Quick Start Information

  • As soon as your shipment arrives, release the crabs into holding containers (plastic pails or other small containers). Do not leave the crabs in their shipping bags.

  • Prepare the holding containers by adding a few centimeters of conditioned water to each one.

  • Open the bags slightly so you can pour out and discard the shipping water. Carefully release the crabs into the pails. If males and females were shipped in separate bags, you will want to keep them separate.

  • Cover the pails to prevent the crabs from escaping. Prepare habitats as soon as possible. For habitat instructions, see the Housing section.

About the Organism

  • Fiddler crabs can be found in salt marshes and on sandy or muddy beaches in West Africa, the Western Atlantic, Eastern Pacific, and the Indo-Pacific.
  • Fiddler crabs are detritovores. They eat by picking up chunks of sediment and sifting through its contents. You can recognize an occupied fiddler crab burrow by the presence of discarded sediment balls at the entrance.
  • The feeding style of the fiddler crab helps preserve wetland environments by aerating the sediment and preventing anaerobic conditions from forming.
  • Fiddler crabs can live up to 3 years in captivity.
  • If a male fiddler crab loses its larger claw, the other will grow larger, and the crab will develop a new, smaller claw.
  • Domain: Eukarya
  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Malascostraca
  • Order: Decapoda
  • Family: Ocypodidae
  • Genus: Uca
  • Species: pugilator

Preparation

Carolina offers a fiddler crab kit that contains the supplies needed to maintain fiddler crabs in the classroom.

Six crabs can live comfortably in a 3- to 5-gallon terrarium. Each terrarium should have a lid.

Housing

Cover the bottom of a terrarium with 4 to 5 cm of sand. Fiddler crabs will usually damage live plants, but you can add a plastic plant or sticks for decoration.

Set a small bowl or dish (plastic or glass) into the sand so that the rim of the bowl is flush with the surface. Fill the bowl halfway with conditioned, dechlorinated water. Always keep the water bowl half full and change the water weekly or when dirty.

There may be a small bag of marine salt taped to the shipping bag, which you can use to make a brackish water solution. Add about 1 g (¼ tsp) of marine salt to 1.5 L of conditioned, dechlorinated water. Offer it just like fresh water. To make your own, you can use any marine salt, rock salt, or non-iodized salt.

Feeding

In captivity, fiddler crabs use their scavenger instincts and will feed on anything they can find. Place a few pieces of dried plankton or brine shrimp flakes into the terrarium, add the crabs, and cover. Fiddler crabs also eat pet food and bits of fruits and vegetables. We sell fiddler crab food in a pellet form that makes it easy to feed fiddler crabs.

Maintaining and culturing

Direct sunlight may kill the crabs, so place the terrarium in indirect light. Maintain at 20 to 25° C (68 to 77° F). The crabs will be more active when warm. Remove dead crabs immediately.

Disposal

Carolina provides living organisms for educational purposes only. As a general policy, we do not advocate the release of organisms into the environment. In some states, it is illegal to release organisms, even indigenous species, without a permit. The intention of these laws is to protect native wildlife and the environment.

We suggest that organisms be:

  • Maintained in the classroom.
  • Donated to another classroom or science department.
  • With parental permission, adopted or taken home by students.
  • Donated to a nature center or zoo.
  • Disposed of humanely, as a last resort.

Fiddler crabs can be chilled to immobility and then frozen. After being frozen for a few days, they can be thawed, sealed in plastic bags, and disposed of.

Biosafety

Wash your hands with soap and water before and after handling living organisms.

Video

No video or video playlist applies for this organism.

FAQs

How do I keep my fiddler crabs healthy?

Keep them at a consistent temperature and change their water regularly.

Do fiddler crabs mate?

You may observe courtship behavior in which the male waves his large claw to attract the female. Usually the male must have a burrow before the female will mate with him. There is not enough sand in the terrarium for the male to excavate a burrow, although he may try.

How long do fiddler crabs live?

In the wild, this is unknown. In captivity, they will most likely live for a school year with good care. They can live up to 3 years.

Can I keep 2 or more males in a terrarium?

Probably. Male fiddler crabs may wrestle, push, and shove each other, especially in the presence of a female. These matches rarely result in injury but may stress the loser.

A crab has molted. What do I do?

Very little. Do not remove the molted skin. The crab will eat it, which provides needed calcium. The crab will be fragile for several days. If another crab is bothering the crab that has molted, remove the other crab for a few days.

Need help?

We want you to have a good experience. Orders and replacements: 800.334.5551, then select Customer Service. Technical support and questions: caresheets@carolina.com

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