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
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).
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
Male cheliped with inner face of carpus lacking tubercle; palm of propodus with low oblique ridge of a tubercles. Go to 3).
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
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
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
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.
Atlantic Mangrove Fiddler
(Smithsonian Marine Station at Ft. Pierce)