Diamondback terrapin (Malaclemys terrapin)

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderTestudines
FamilyEmydidae
GenusMalaclemys (1)
SizeMale length: up to 15 cm (2)
Female length: up to 23 cm (2)

The diamondback terrapin is classified as Near Threatened (NT) on the IUCN Red List (1).

The diamondback terrapin (Malaclemys terrapin) was once almost pushed to extinction due to a fashion among some members of American society for turtle meat, a trend that thankfully died out before this terrapin did (3). The diamondback terrapin has an oblong upper shell (carapace) that is grey, light brown or black and patterned with concentric diamond-shapes (4). The shell on the underside of the terrapin (the plastron) can range in colour from yellowish to green or black, and may be decorated with bold, dark markings (3). The grey or black skin of the limbs and head bears dark flecks and spots, the head is short and flat, and the prominent eyes are black (3) (4).The large, webbed feet are adapted for swimming, but also bear strong claws that allow the terrapin to clamber up out of the water (3) (5). Female diamondback terrapins are larger than the males, and have a broader head and shorter tail (3). Juveniles are patterned much like adults but usually brighter and have rounder shells (6).

The diamondback terrapin is native to the United States, where it occurs along the Atlantic and Gulf coasts from Cape Cod to Texas (3).

The diamondback terrapin inhabits the brackish waters of coastal marshes, tidal flats, coves, estuaries and coastal lagoons (4).

Active during the day, the diamondback terrapin spends its time basking on land and feeding on a variety of worms, crabs, snails and fish (3) (5). The female, with its broader heads and crushing jaws, is well-adapted for eating hard-shelled prey, including salt marsh periwinkles (Littorina irrorata), small bivalves, barnacles, and crabs (4), while the smaller, narrower-headed male generally eats smaller prey and softer prey items such as worms, fish and some plant material (4) (6).

Courtship and mating occur from late March to May, and begin with a male approaching a female in the water and nuzzling or nudging her cloacal region with his snout. If the female remains still, the male mounts immediately and copulation occurs at the surface, but if the female swims away, the male may pursue her for long distances (3). Females lay their eggs from April through July (4), typically during the day, although females do not nest during heavy or prolonged rains (7). The nests, which are flask-shaped egg chambers, measuring up to 20 centimetres deep and 10 centimetres wide, are located above the high-tide mark along the sandy edges of salt marshes and rivers, in the dunes of sea beaches, and on offshore islands. Females produce at least two, and sometimes up to five, clutches a year, with each clutch containing from 4 to 22 leathery, dimpled, pinkish-white eggs. Female diamondback terrapins in the southern part of the range have been found to produce fewer but larger eggs than females in the north (3) (7). Research indicates that, like many other reptiles, the diamondback terrapin has temperature-dependent sex determination; that is, when eggs are incubated at low temperatures male hatchlings are produced, while incubation at higher temperatures results in female hatchlings (6).  After 9 to 15 weeks, the eggs hatch, and the young may remain in the nest for the first winter, before emerging in April and May to head for brackish waters (6). If the hatchlings successfully avoid predation (for example, from gulls, crows and black-crowned night-herons), male diamondback terrapins mature before the end of their third year whereas females mature after their sixth year (4). Individuals may live for 25 to 40 years (6).

For many years, the diamondback terrapin was highly prized for its meat. Harvesting of this species from the 1880s until the 1930s was so rife that the diamondback terrapin was almost brought to extinction (5). Thankfully, the introduction of protection laws for this species in a number of states, combined with a decrease in demand as the fad for this ‘gourmet’ food died out, enabled populations to recover (2). Today this small reptile is still occasionally exploited for food, but hunting is no longer the greatest threat it faces (3).

One of the major threats to the diamondback terrapin is incidental drowning in crab traps (3); this turtle's desire for the dead fish bait has led to many being trapped and drowned in both commercial and recreational crab pots (3). Due to the entrance size of crab traps, the smaller male terrapins are more likely to be caught, disrupting local sex ratios (3) (8).

Other threats include commercial harvesting for the pet trade, coastal development and pollution, incidental kills by motor boat propellers, and road mortality (especially of nesting females), all of which are resulting in diamondback terrapin populations declining once again (3).

The diamondback terrapin is currently offered varying amounts of protection in the states in which it occurs (6) (9) (10). For example, in Connecticut, this species can no longer be collected or possessed (6), while in New York State a licence is required to take diamondback terrapins from the wild, and size limits on catches have been established (9).

Modifications to crab traps, such as the installation of simple terrapin excluder devices, would save the lives of many terrapins. One of the most effective devices is a simply a small rectangle of wire that reduces the size of the entrance, allowing crabs to still entering while keeping large terrapins out (3). At least three states (New Jersey, Maryland and Delaware) have implemented regulations that state such terrapin excluders must be used under certain circumstances (11), although it is clear that more widespread use of such devices would help ensure the future of the diamondback terrapin.

Learn more about the conservation of the diamondback terrapin:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

  1. IUCN Red List (April, 2011)
    http://www.iucnredlist.org
  2. Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Marshall Cavendish, New York.
  3. Ernst, C.H. and Lovich, J.E. (2009) Turtles of the United States and Canada. Second Edition. The Johns Hopkins University Press, Baltimore, Maryland.
  4. Ernst, C.H., Altenburg, R.G.M. and Barbour, R.W. (1997) Turtles of the World. ETI Information Systems Ltd, Netherlands. Available at:
    http://nlbif.eti.uva.nl/bis/turtles.php
  5. Day, L. (2007) Field Guide to the Natural World of New York City. The Johns Hopkins University Press, Baltimore, Maryland.
  6. Department of Environmental Protection, State of Connecticut (May, 2010)
    http://www.ct.gov/dep/cwp/view.asp?A=2723&Q=326000
  7. Burger, J. and Montevecchi, W.A. (1975) Nest site selection in the terrapin Malaclemys terrapin. Copeia, 1975: 113-119.
  8. NatureServe Explorer (May, 2010)
    http://www.natureserve.org/explorer
  9. Department of Environmental Conservation, New York State (May, 2010)
    http://www.dec.ny.gov/reg/4045.html#12864
  10. Brennessel, B. (2006) The Northern Diamondback Terrapin Habitat, Management and Conservation. The Northeast Diamondback Terrapin Working Group, USA. Available at:
    http://www.dtwg.org/Bibliography/Gray/Brennessel%202007.pdf
  11. Terrapin Conservation at the Wetlands Institute (May, 2010)
    http://www.terrapinconservation.org