Description: The common name refers to the diamond pattern on top of its shell (carapace), but the overall pattern and coloration vary greatly. The shell is usually wider at the back than in the front, and from above it appears wedge-shaped. The shell coloring can vary from brown to grey, and its body color can be grey, brown, yellow, or white. All have a unique pattern of wiggly, black markings or spots on their body and head. The diamondback terrapin has large webbed feet. The species is sexually dimorphic in that the males grow to a carapace length of approximately 5 inches, while the females grow to an average carapace length of around 7+1/2 inches, though they are capable of growing larger. The largest female on record was just over 9 inches in carapace length. Specimens from regions that are consistently warmer in temperature tend to be larger than those from cooler, more northern areas. Male diamondback terrapins weigh 11 ounces on average, while females weigh around 18 ounces. The largest females can weigh up to 35 ounces.
Habitat: Diamondback terrapins live in brackish water habitats state-wide, including salt marshes, barrier islands, mangrove swamps, tidal creeks and rivers. Little is known about terrapin habitat use during the winter, but in cold weather terrapins may become less active and bury themselves in the muddy substrate under water, beneath undercut banks or in soft sand or mud on banks of rivers, creeks or marshes.
Range: Found along the tip of Florida down through the Florida Keys.
Diet: The diamondback terrapin typically feeds on fish, crustaceans (such as shrimp and crabs) marine worms, marine snails (especially the saltmarsh periwinkle ), clams, barnacles, mussels, other mollusks, insects, carrion, and sometimes ingest small amounts of plant material, such as algae. At high densities the terrapin may eat enough invertebrates to have ecosystem-level effects, partially because periwinkles themselves can overgraze important marsh plants, such as cordgrass (Spartina alterniflora). Gender and age can greatly affect the diet of the diamondback terrapin, males and juvenile females tend to have less diversity in their diet. Adult females, due to their powerful, defined jaw, will occasionally feed on crustaceans such as crabs and are more likely to consume hard-shelled mollusks.
Reproduction: Like all reptiles, terrapin fertilization occurs internally. Courtship has been seen in May and June, and is similar to that of the closely related red-eared slider (Trachemys scripta). Female terrapins can mate with multiple males and store sperm for years, resulting in some clutches of eggs with more than one father.
Like many turtles, terrapins have temperature dependent sex determination, meaning that the sex of hatchlings is the result of incubation temperature. Females can lay up to three clutches of eggs/year in the wild, and up to five clutches/year in captivity. It is not known how often they may skip reproduction, so true clutch frequency is unknown.
Females may wander considerable distances on land before nesting. Nests are usually laid in sand dunes or scrub vegetation near the ocean in June and July, but nesting may start as early as late April in Florida. Females will quickly abandon a nest attempt if they are disturbed while nesting. Clutch sizes vary latitudinally, with average clutch sizes as low as 5.8/eggs/clutch in southern Florida to 10.9 in New York. After covering the nest, terrapins quickly return to the ocean and do not return except to nest again.
The eggs usually hatch in 60–85 days, depending on the temperature and the depth of the nest. Hatchlings usually emerge from the nest in August and September, but may overwinter in the nest after hatching. Nest predation is a large threat to Diamondback Terrapins. A study was done on 3159 nests finding that the greatest predator was racoons and predated nests were completely emptied of egg. Hatchlings sometimes stay on land in the nesting areas in both fall and spring and they may remain terrestrial for much or all of the winter in some places. Hatchling terrapins are freeze tolerant, which may facilitate overwintering on land. Hatchlings have lower salt tolerance than adults and Gibbons et al. provided strong evidence that one- and two-year-old terrapins use different habitats than do old individuals.
Growth rates, age of maturity, and maximum age are not well known for terrapins in the wild, but males reach sexual maturity before females because of their smaller adult size. In females at least, sexual maturity is dependent on size rather than age. Estimations of age based on counts of growth rings on the shell are as yet untested, so it is not clear how to determine the ages of wild terrapins.
Status: The species is classified as Near Threatened by the IUCN due to decreasing population numbers in much of its range. There is limited protection for terrapins on a state-by-state level throughout its range; it is listed as Endangered in Rhode Island and Threatened in Massachusetts. The Diamondback Terrapin Working Group deal with regional protection issues. There is no national protection except through the Lacey Act, and little international protection.
Disclaimer: ITIS taxonomy is based on the latest scientific consensus available, and is provided as a general reference source for interested parties. However, it is not a legal authority for statutory or regulatory purposes. While every effort has been made to provide the most reliable and up-to-date information available, ultimate legal requirements with respect to species are contained in provisions of treaties to which the United States is a party, wildlife statutes, regulations, and any applicable notices that have been published in the Federal Register. For further information on U.S. legal requirements with respect to protected taxa, please contact the U.S. Fish and Wildlife Service.
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