The Diamondback Terrapin (Malaclemys terrapin) is an attractive medium sized, brackish water turtle of the family Emydidae. It is semi-aquatic in nature and ranges along the eastern and southern coasts of North America, from Cape Cod to Corpus Christi. Diamondbacks are the only U.S. turtles that inhabit estuaries, tidal creeks and saltwater marshes where the salinity comes close to or equals that of the ocean. It is in this type of environment that diamondbacks thrive, dining on delicacies such as crabs, snails, shrimp, fish, mussels, clams, and other assorted crustaceans.
Diamondback terrapins have proven to be one of the most physically variable of turtle species and even specimens within the same subspecies/populations can have vastly differing shell pattern, skin color, markings and shapes. However, one trait that is characteristic of all diamondbacks is their grooved, concentrically patterned, diamond-shaped scutes. It is from these intricate markings that the diamondback has derived its name. In addition, another descriptive feature of diamondbacks, shared with their common relatives the Map turtles (Graptemys sp.), is their sexual dimorphism. Females tend to be twice the size of males at sexual maturity. Male diamondbacks usually attain a carapace length of 5 inches, whereas females can attain a length of 9 inches. Females also possess larger and broader heads than males, adding to their stouter, bulkier look. A last distinguishing trait of diamondbacks is the large size of their hind feet in proportion to their bodies. This adaptation gives them greater mobility under the onslaught of strong tidal currents and undertows.
The color of diamondback carapaces can vary from black, brown, gray, orange, olive to tan; their patterns from concentric marbles, donuts, to patternless. In addition, their carapaces can be either deeply or slightly grooved, sporting either huge vertebral keels or slight knobs. Diamondback skin color and pattern are equally diverse with colors ranging from gray, white, olive, slate blue to even black; and patterns range from small dots, big spots, lines, bold stripes, combination of spots and lines, and patternless. To further complicate things, the intergrading of populations when commercial harvesting was at its peak further confounded taxonomical identification at the sub-specific level. Terrapin meat was once greatly esteemed as a delicacy from the late 1800s' into the Roaring Twenties; hence the reason for commercial harvesting (the word "terrapin" was actually derived from a french word meaning turtle soup). When the demand for terrapin meat finally waned due to the stock market crash and Prohibition (terrapin meat was usually cooked with wine), large shipments of diamondbacks from various parts of their range were reported to have been released into the wild. The introduction of these shipments compromised the purity of native populations and hence complicated the identification of the east coast subspecies.
There are currently seven recognized diamondback subspecies: the Northern Diamondback Terrapin (M.t. terrapin), the Carolina Diamondback Terrapin (M.t. centrata), the Florida East Coast Diamondback Terrapin (M.t. tequesta), the Mangrove Diamondback Terrapin (M.t. rhizophorarum), the Ornate Diamondback Terrapin (M.t. macrospilota), the Mississippi Diamondback Terrapin (M.t. pileata) and the Texas Diamondback Terrapin (M.t. littoralis). These subspecific delineations were mainly based on phenotypic differences. With this in mind, some have proposed splitting the Mangrove Diamondback Terrapin into Upper Keys and Lower Keys subspecies due to their differing phenotypes. To further complicate things, diamondback terrapins have also been found in Bermuda. They appear to be native, appear identical to the Carolina Diamondback Terrapin and have yet to be categorized.
Recently, genetic studies have further narrowed the species down to four regional genetic clusters: Northeast Atlantic (MA), Coastal Mid-Atlantic (NY to SC), FL and TX/LA. However, further sampling must occur to substantiate these findings so for now, we will continue our taxonomic discussion based on the accepted seven subspecies.
Diamondback Terrapin (Malaclemys terrapin) subspecies (A-G dotted area, see Ernst et al. 1994) designations and new genetic groupings (1-4). A "*" indicates locations with no samples.