Diamondback Terrapin Natural History

Diamondback terrapins are the only exclusively estuarine turtle in the United States, with populations along the eastern coast from Massachusetts to Texas. Throughout much of the year, they may be found in and around tidal creeks. In these areas, they eat a variety of hard-bodied prey including fiddler crabs, periwinkle and mud snails. Because these snails consume the grasses that stabilize the salt marsh, predation by diamondback terrapins may help to maintain the integrity of salt marsh habitat for estuarine organisms.

Diamondback terrapins are sexually dimorphic meaning that males and females are different sizes. Females attain much larger sizes than males. Terrapins breed in late spring and early summer. Female terrapins must leave the marsh to lay eggs in nests located above the high tide line. During these breeding movements, they can encounter many dangers including predators and human development including roads.

Terrapin color patterns are highly variable with individuals that are almost solidly black to those with green and orange shells. They can have light to dark colored heads, and some even have dark mustaches! For these patterns, diamondback terrapins have been called “jewels of the marsh.”

Diamondback Terrapin Threats

Coastal development: Diamondback terrapins must nest on land above the high-tide line where they encounter human development. Roads are one primary threat where female terrapins can be hit by cars while trying to find suitable nesting habitat. Roads can also increase rates of nest predation by predators like raccoons and outdoor cats by providing wide corridors for travel and easier access to terrapin nests. Finally, development can create other pitfalls for terrapins seeking nesting habitat. Retaining walls block access to nesting locations and other types of land manipulation can trap adult females or hatchling terrapins. 

Crab fishing: Diamondback terrapins are attracted to the same baits as blue crabs. Because terrapins cannot breathe underwater like crabs, they drown when they investigate and enter crab pots. Further endangering these animals, terrapins appear especially attracted to crab pots already containing other trapped terrapins. Because of the entrance size of conventional crab pots, only the largest females are excluded from entry to the traps. We encourage the use of bycatch reduction devices oriented vertically to prevent entry by all but the smallest terrapins.

Climate change: Diamondback terrapins rely on the narrow area of land between high ground and sea for nesting. Salt marsh habitats can vary with small differences in how long flooding occurs at high tide. As sea levels rise, higher water levels minimize the availability of high marsh and more intense storms with higher tides erode tidal creeks and reduce the size of salt marsh habitat. Finally, ocean overwash during these storms can flood terrapin nests, preventing successful embryonic development.