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Fiddler Crab Identification Key

Interesting Gulf & Coastal Fishes

Identification Guide to Fiddler Crabs
Of the Northern Gulf Coast

This key will assist in the identification of the give common species of adult fiddler crabs (Genus Uca) from the intertidal zone of the Mississippi Gulf Coast. The key is based largely on male characters and coloration in living specimens. Click on a photo to open a larger version.

1) Chela palm (inner face of manus on propodus) lacking a distinct tubercular ridge.  Carapace with cardiac depression rust-read or purplish-red, appearing hourglass-shaped.  Major male cheliped  with carpus and propodus (palm) reddish orange to purplish red.   Uca panacea   

fiddler crab identification guide, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. HeardUca panacea, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Else

Chela with palm having an oblique ridge of tubercles of varying sizes.   Carapace and chela with different pigmentation,  lacking rust-red orange or purplish-red coloration. Go to 2).

fiddler crab identification guide, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

2) Male cheliped with inner face of carpus usually with a tubercle, palm of propodus with raised, pyramid–like ridge of tubercles. (Chela whitish with long narrow fingers; carpal joints unpigmented)     Uca spinicarpa

 fiddler crab identification guide, , Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. HeardUca spinicarpa, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Else                     

Male cheliped with inner face of carpus lacking tubercle; palm of propodus with low oblique ridge of a tubercles.  Go to 3).

fiddler crab identification guide, , Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

3) Frontal margin of carapace with mosaic colors including reddish brown-maroon-greenish-reticulated pigment patterns.  Male major chela with lacking orange or reddish pigmentation. Third ambulatory or walking leg with setae sparse on margins of carpus and merus. (detailed photo)  Uca rapax   

Uca rapax, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Else

Frontal margin of carapace whitish or cream or greenish blue.  Male major cheliped with carpal joints light orange to bright red.  Third walking leg with numerous marginal setae on carpus and merus. (detailed photo Goto 4).

4) Frontal margin of carapace usually bright greenish blue.  Male major cheliped having yellowish coloration, carpal joints pale orange.  Uca longisignalis

Uca longisignalis, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Else

Frontal margin of carapace usually whitish or cream-colored. Male major cheliped having whitish and grayish coloration; carpal joints reddish orange to red.  Uca minax

Uca minax, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Reference: "Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico," Richard W. Heard, Mississippi Alabama Sea Grant Consortium, MASGP-79-004, 82 pages.

Other Fiddler Crabs Around the Gulf of Mexico

The key does not include the western Gulf species, Uca subcyclindrica, which restricted to the mud flats of Lagoon Madre; Uca thayeri, which occurs in mangrove habitats along the Florida West Coast from Tampa Bay southward into the Florida Keys; Uca speciosa, which occurs sporadically in the northern Gulf but is common along the West Coast of Florida; U. pugilator which occurs on the on the US East Coast from Massachusetts southward to Florida and along the Gulf coasts to as far west as the Pensacola area.

Click a thumbnail image for a larger view.

Uca subcylindrica, fiddler crabs Uca thayeri, fiddler crabs Uca speciosa, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard Uca pugilator, Guide to Common Tidal Marsh Invertebrates of the Northeastern Gulf of Mexico, Richard W. Heard

Uca subcylindrica
Laguna Madre Fiddler
(photo by Chris Lukhaup)

Uca thayeri
Atlantic Mangrove Fiddler

(Smithsonian Marine Station at Ft. Pierce)
Uca speciosa
Longfinger Fiddler

U. pugilator
Atlantic Sand Fiddler