Basic Facts About Diamondback Terrapins

Named for the diamond-shaped growth rings on its top shell, the diamondback terrapin (Malaclemys terrapin) a turtle native to the eastern and southern United States.


Diamondback terrapins consume fish, snails, worms, clams, crabs and marsh plants.


The diamondback terrapin is found along the Atlantic Coast of the eastern United States from Cape Cod to the Florida Keys and west along the Gulf Coast to Texas.


The diamondback terrapin is believed to be the only turtle in the world that lives exclusively in brackish water (containing some salt, but not as much as ocean water), habitats like tidal marshes, estuaries and lagoons. Most terrapins hibernate during the winter by burrowing into the mud of marshes. Although diamondback terrapins live in tidal marshes, estuaries and lagoons, their preferred nesting sites are sandy beaches.


Mating Season: May through July.
Gestation: Around 60 days.
Clutch size: 8-12 eggs.

The gender of diamondback terrapin offspring is determined by temperature – a higher nest temperature produces more females while a lower nest temperature produces more males.

The hatchlings emerge from August to October and are completely on their own. Only 1 to 3% of the eggs laid produce a hatchling, and the number of hatchlings that survive to adulthood is believed to be similarly low.

After hatching, some young remain in the nest during the winter although most emerge and enter the nearest body of water.


The diamondback terrapin is threatened by habitat destruction, road construction (terrapins are common roadkill) and drowning in crab traps.

Climate change is also poised to bring major changes to the terrapin’s habitats and life cycle. By the end of this century, sea level is projected to rise between 2.25 feet under a low emissions scenario and up to 3.25 feet under the highest emissions scenario.

Due to land subsidence in the Northeast, the effect of the rise will seem about 10 to 20% higher than the actual. Salt water incursion into brackish tidal marshes will alter their character and potentially make large areas saltier than the terrapin can tolerate. Storm surges and beach erosion threaten their preferred nesting habitats. And higher temperatures on nesting beaches could skew the sex ratios of offspring.

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In the Magazine
Alexandra Siess finished a hard day’s work retrieving nets used to catch and then count, measure, tag and release diamondback terrapins in the Chesapeake Bay