Fiddler Crabs
Of the Northern Gulf Coast

Fiddler crab, note enlarged claw of male crabFiddler crabs are small semi-terrestrial crabs that inhabit tidal marshes and the adjacent sand and mud flats. They are recognized by the square shape of their bodies and by the male fiddler's oversized claw. Fiddlers dig cylindrical burrows where they take shelter from predators, hot sun, winter cold, and high tides. Fiddler crabs typically live in colonies; if you find one, you're likely to find dozens nearby.

Fiddler crabs are named for the distinctive waving movements made by the males with their enlarged claw during courtship. The motion resembles a musician playing a fiddle or violin. Each species has a distinct waving motion. The motion of the feeding claws on both males and females also resembles a fiddling motion. In Peru, the motions are compared to sewing and fiddlers are called maestro-sastres or master tailors. Their names in Japan (Siho Maneki) and in Brazil (Chama Marés) interprets the fiddler's motions as beckoning for the tide to return.

The video below shows typical male fiddler crab waving behavior. Additional video links are provided at the end of this page.

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Male Gulf Mud Fiddler Displaying, Uca longisignalis
Video by Don Abrams

Taxonomy

Classification Characteristic
Kingdom: Animalia Multicellular, complex cells with structures enclosed in membranes
Phylum: Arthropoda Exoskeleton (external skeleton), segmented body, & jointed appendages
Subphylum: Crustacea Branched and segmented appendages
Class: Malacostraca 20 body segments (rarely 21), divided into a head, thorax and abdomen
Order: Decapoda "Ten footed", five pairs of appendages attached to the thorax
Infraorder: Brachyura Abdomen is small and entirely hidden under the thorax
Family: Ocypodidae One enlarged claw
Genus: Uca Square body

Five species of fiddler crabs are found on the Mississippi coast. Photographs are provided in the table below. Differences in species are often subtle. A taxonomy guide to northern Gulf coast fiddler crabs is provided here.

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Uca panacea, Panacea Sand Fiddler, , Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca panacea
Panacea Sand Fiddler

  • Distribution: Gulf of Mexico from Panacea in the Florida panhandle to the Tabasco-Campeche border in Mexico
  • Habitat: intertidal salt marshes and sand flats, on sand or sandy mud substrata
  • Carapace width: 18
  • Similar to Uca pugilator found to the east, beginning near Pensacola, Florida
Uca spinicarpa, Spinded Fiddler Crab, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca spinicarpa
Spined Fiddler Crab

  • Distribution: Gulf of Mexico from Alabama to Tabasco, Mexico
  • Habitat: Fresh to brackish water, intertidal banks and marshes with firm clay, clay-sand, or clay-mud substrata
  • Carapace width to 23 mm
Uca minax, Red Jointed Fiddler Crab, Fresh-Water Fiddler Crab, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca minax
Red Jointed Fiddler crab, Fresh-Water Fiddler

  • Distribution: Massachusetts to central eastern Florida and western central Florida to Louisiana. Not found found of Daytona and Crystal River in Florida.
  • Habitat: Low-salinity and freshwater marshes, usually near river mouths, muddy substrata
  • Carapace width to 33 mm
Uca longisignalis, Gulf Mud Fiddler, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca longisignalis
Gulf Mud Fiddler

  • The most common fiddler in Mississippi and Alabama salt marshes
  • Distribution: Western central Florida to Texas
  • Habitat: Moderately salty salt marshes on mud to mud-sand substrata
  • Carapace width to 26 mm
Uca rapax, Mudflat Fiddler, , Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca rapax
Mudflat Fiddler

  • Distribution: Southern Florida; Alabama to Texas; Caribbean and Atlantic coasts of Central America, Gulf coast of Mexico, and northern South America and Brazil
  • Habitat: Moderately salty to salty salt marsh and mangrove areas, sandy-silt substrata
  • Carapace width to 23 mm

Two additional species of fiddlers occur on the northern Gulf coast.

Uca pugilator, Sand Fiddler, Calico Fiddler, , Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca pugilator
Sand Fiddler Crab or Calico Fiddler

  • Distribution: Massachusetts to Pensacola, Florida
  • Habitat: intertidal salt marshes and sand flats, on sand or sandy mud substrata
  • Carapace width to 25 mm
  • Similar to Uca panacea; ranges overlap between Pensacola and Panacea, Florida. 
Uca speciosa, Longinger Fiddler, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca speciosa
Longfinger Fiddler

  • Distribution: South Florida from Daytona on the east to Alligator Point on the west. Occasionally to Mississippi, but only on the offshore islands of Alabama and Mississippi; Yucatan peninsula in Mexico; Cuba and the Bahamas
  • Habitat: Moderately salty to salty salt marsh and mangrove areas, silt or silty sand substrata
  • Carapace width to 15 mm

Photos from "Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico," Richard W. Heard.

Similar Species

 

Fiddler crabs are closely related to the ghost crab, Ocypode quadrata. Ghost crabs are larger and very light in color. Ghost crabs prefer open sandy beaches rather than tidal marshes, and they're much larger than fiddlers.

 

Ghost crab, Ocypode quadrata

Photo by Chris Snyder

 

Fiddler crabs also resemble crabs in the family Grapsidae, commonly known as marsh crabs, friendly crabs, shore crabs, square backed crabs, or wharf crabs. Male Grapsidae crabs lack the enlarged claw of male fiddlers.

 

 

The Grapsidae family of crabs includes commonly known as marsh crabs, friendly crabs, shore crabs, square backed crabs, or wharf crabs.  They are similar to fiddler crabs.

Photo by Robert Lord Zimlich

Anatomy & Physiology

Fiddler crab anatomy

Original image credit: By Christopher Thomas [via Wikimedia Commons"

Range and Habitat

Fiddlers live in in the inter-tidal zone of marshes and the adjacent mud and sand flats. They always live close to water, with particular species adapted to a wide range of salinity. The species described here exist along the entire northern coast of the Gulf of Mexico.

Feeding

Fiddlers are deposit feeders and scavengers, ingesting a variety of food including detritus (decayed organic matter), nematodes (small worms with unsegmented cylindrical bodies), bacteria, fungi, algae, and decaying animal matter. The females have both their small claws adapted for feeding. The male cannot use his large claw for feeding; therefore, he must use the small claw much more rapidly in order to eat the same amount as a female during the same period of time. Despite this feeding disadvantage, male fiddlers are usually larger than females.

Female Male
Gulf Mud Fiddler crabs feeding, Uca longisignalis
Videos by Don Abrams

Fiddler crabs feed on the falling tide and are most active at low tide when the greatest area of exposed mud flats exists. As the tide rises, the fiddlers retreat to their burrows and seal the entrance with a mud ball plug. Fiddlers may range as far as 50 yards from their burrows while feeding.

When feeding, the sand fiddler takes sandy material into its mouth (buccal cavity) and uses specialized spoon-shaped setae on its maxillipeds to scour the algae and other organic matter off the sand grains. As the sand grains are cleaned, the crab forms the grains into "feeding balls" or "pseudo-feces" which are discarded. Often large concentrations of pseudo-feces occur around the openings of the burrows of sand fiddlers. Similar balls, usually larger, are formed with material that the crab brings to the surface when excavating a burrow.

Fiddler crab burrow with feeding balls and excavation balls feeding.and.excavation.balls.beach.320.jpg
Fiddler crab burrow.
Note the larger excavation balls at the lower right portion of the photo. The smaller balls are feeding balls.
Field of fiddler crab excavations and feeding activity show the effect of fiddlers on their habitat.
Click either image for a larger view. Photos by Don Abrams.

One study found that the Gulf mud fiddler crab takes in approximately 0.4 g of material in six hours. Foods eaten have been estimated to be 33% diatoms, 25% fungi, 20% vascular plants, and 20% unknown material. (Grimes, Huish, and Kerby, September 1989; Ringold, 1979)

Place in the Food Web

Fiddler crabs make up an important part of the diet of many coastal animals, including blue crabs, mud crabs, purple marsh crabs, red drum, diamondback terrapins, willets, gulls, rails, herons, rice rats,
and raccoons.

Fishermen find fiddler crabs an effective bait, especially for sheepshead, pompano, and both red and black drums.

The sensitivity of fiddlers to pollutants, heavy metals, and pesticides makes them a good indicator of the health of an ecosystem. In building their burrows, fiddlers provide a beneficial effect on the marsh by aerating the soil and bringing organic matter to the surface. As they sift though the sands while feeding, they aerate the substrate and prevent anaerobic conditions (decay without oxygen present).

Behavior

The male fiddler crab uses his large claw in courtship and in combat against other males during territorial disputes. Courting males wave their large claws in rhythmic patterns that are unique to each species of Uca. The Panacea sand fiddler male uses it to produce a rapid, drumming sound. The sound apparently is caused by the claw striking either the edge of the fiddler's carapace or the ground.

Fiddlers take refuge from predators and high tides in their burrows. As the tide rises, they seal the entrance with a pellet of mud and wait out the high water while breathing trapped air.

Fiddler crabs recognize their own burrows, but when threatened they will escape into any convenient burrow. Fiddlers may also burrow into the sand to escape from predators. When the danger has passed, they emerge and resume their normal behavior.

Fiddler crabs move sideways, never forward or backward.

A territorial dispute between two Gulf mud fiddler crabs from adjacent burrows, Uca longisignalis.
Video by Don Abrams

Life Cycle & Reproduction

The male fiddler digs, maintains and defends a tidy, cylindrical burrow that is L-shaped with a single opening. The burrows are usually no more than about 14 inches deep, but sometimes as deep as 24 inches.

To find a female partner, the male stands next to his burrow, often near other males standing next to their own burrows, while females walk past. The male waves his major claw to attract the female's attention.

If a female is interested, she will stare at the male for a short period of time. The male then runs toward the female and runs back to his burrow, repeating this motion several times until the female either moves on or follows him to the burrow. If the female follows, the male partly enters the burrow and drums the edge with his claw, then leads the female inside, plugs the entrance and returns to the female to mate.

Unlike most other crabs, fiddlers don't have to wait to mate until the female has recently molted and her exoskelton is still soft. The female incubates her sponge, or eggs, for two weeks, then returns to the surface to release them into the water, where they hatch and develop into juveniles. The number of eggs per clutch varies by species and with the size of the individual crab, typically 10,000 to 40,000 for northern Gulf Coast fiddlers.

From April to October, Mississippi coast fiddler crabs can produce larvae every two weeks. Their release is usually timed to the highest tides, probably so that the ebb flow takes them to deeper water. From November to March, low temperature inhibits reproduction.

The planktonic larvae go through two to five zoeal stages before becoming bottom-dwelling megalopa and then finally metamorphosing into a juvenile crab as they return to the marshes. Depending on the species, the process from egg to adult takes a few weeks to months. Fiddlers typically have a life span of one to two years.

Interesting Facts About Fiddlers

Resources and References

Websites & Publications

Uca longisignalis, Gulf Mud Fiddler Crab, Gulf of Mexico, Mississippi
  Photo by Don Abrams

Fiddler Crab Videos on Youtube

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