Photograph by Joel Sartore, National Geographic Photo Ark
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The Texas diamondback terrapin (Malaclemys terrapin littoralis), a subspecies of terrapin, is seen at the Houston Zoo.

Photograph by Joel Sartore, National Geographic Photo Ark

Diamondback terrapin

About the diamondback terrapin

The diamondback terrapin is an iconic turtle of the coastal salt marshes of the northeastern United States. Found throughout estuaries, shallow bays, and tidal creeks, these reptiles prefer brackish water, but also need periodic access to fresh water to avoid dehydration. Salt glands around their eyes allow them to secrete excess salt from their bloodstream.

The terrapin’s shell is covered with its namesake diamond-shaped scutes, or bony plates. Each scute has concentric growth rings at the center, which have been often cited—perhaps erroneously—as a way to estimate their age.

The diamondback’s striking skin can range from white to dark gray or even bluish with black markings. There are seven recognized subspecies throughout their range, which runs along the Atlantic coast from Massachusetts, south to Florida, around the Gulf of Mexico, and down to southern Texas.

Terrapins eat mussels, crabs, clams, and snails, but can also eat carrion, insects, worms, plants, and algae.

Mating and reproduction

“Fast and furtive” is how author Barbara Brennessel described the courtship and mating of diamondback terrapins, which begins in early spring. The female floats on the water, waiting for a male to approach. If she remains still, mating takes place right away, but if she swims away, he may pursue her for long distances. Females often mate with multiple males.

Females come ashore to sandy beaches or dunes to lay their eggs in June or July, forming triangular-shaped nests about four to eight inches deep. Northern subspecies tend to be larger and lay more eggs, but overall a clutch could be anywhere between four to around 25 pinkish-white, leathery eggs. The young hatch between August and September, and are vulnerable to land predators, including foxes and raccoons.

Conservation status

The International Union for Conservation of Nature lists the diamondback terrapin as vulnerable to extinction. A main threat is accidental drowning in commercial blue crab traps. If the trap is abandoned, the decomposing animal will attract other animals, including other terrapins, creating a vicious cycle of mortality. Terrapin excluder devices can allow the animals to escape the traps, and in some fisheries, these devices are mandatory.

Other human causes, such as coastal development, also result in terrapin habitat destruction and pollution. Females and hatchlings are sometimes killed by vehicles or trapped in storm drains.

Sea-level rise due to climate change could also destroy terrapin nesting habitat.