University of Massachusetts Amherst

Massachusetts North American Amphibian Program

Diamond-backed Terrapin

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Herp Atlas 1992-1998 Survey

  • The map below shows the distribution of the Diamond-backed Terrapin in Massachusetts based on the original intensive volunteer survey that took place from 1992-1998.
  • Download pdf of map

Updated Distribution Map

Malaclemys terrapin (4-9”)
MA Status: "Threatened." Illegal to harass, kill, collect or possess.

Diamond-backed Terrapin
Diamond-backed Terrapin

The Diamond-backed Terrapin is a medium-sized salt marsh turtle. It has a wedge shaped carapace (top shell) variably colored in ash grays, light browns, greens and blacks. It has concentric ring patterns on the carapace and a pronounced ridged or bumpy mid-line keel. Both sexes have grayish to black skin, spotted with dark green flecks and light colored upper and lower jaw. This turtle has very large, paddle like hind feet that are strongly webbed. Adult females are considerably larger than males ranging from 6-9 inches in length, while males are 4-6 inches. Hatchlings look like adults and are about 1 inch long.

Diamond-backed Terrapins inhabit marshes which border quiet salt or brackish tidal waters. They can also be found in mud flats, shallow bays, coves, and tidal estuaries. Adjacent sandy dry upland areas are required for nesting. Diamond-backed Terrapins overwinter in the bottom of estuaries, creeks and salt marsh channels. In late spring, males and females gather to create mating aggregations in small, quiet coves along the coast. Salt marshes are critical wintering, foraging, and nursery areas. Egg-carrying females will make the journey upland and sometimes inland as much as 1/4 mile to lay eggs. Except when basking, males spend their time in water; females venture onto land normally twice a year for nesting, once in early June and once in July. Females travel from water’s edge to nesting habitat usually at high tide to reach sites above the high water line. Hatchlings and juveniles are thought to hide out among the grasses in brackish water marshes.

Diamond-backed Terrapins feed on crabs, mollusks, crustaceans, insects, fish, and carrion. They forage in the water. A single female may lay 1-3 nests per year. The female digs a nest about 4-8 inches deep and then deposits a clutch of approximately 12 eggs. Most females exhibit nest site fidelity, where they return to the same nesting location year after year.

On Cape Cod, Diamond-backed Terrapins have been observed nesting during both day and night and on both vegetated and unvegetated uplands; in contrast, southern populations have reported nesting only during the day and only on vegetated dunes. Diamond-backed Terrapins have temperature dependant sex determination; eggs will develop into males if temperatures are below 82° F and at temperatures above 86° F females will develop. At temperatures ranging from 82-86° F there will be a mixture of males and females.

Incubation of eggs in Massachusetts lasts between 59 and 116 days depending on temperature. It may take from 2 to 11 days after the eggs hatch for the young turtles to emerge and start the hazardous trip from the nest to the water. When the climate is unseasonably cold, some hatchlings may overwinter in their nests waiting until the following May to erupt from the sand.

Adapted from the MA Natural Heritage and Endangered Species Program’s Diamond-backed Terrapin fact sheet. 2008



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