New World pond turtles

(Emydidae)

Class Reptilia

Order Testudines

Suborder Cryptodira

Family Emydidae

Thumbnail description
Small- to medium-sized turtles; carapace may be depressed, domed, or strongly keeled; plastron may or may not be hinged; double articulation found between the fifth and sixth cervical vertebrae

Size
10–24 in (25–60 cm)

Number of genera, species
12 genera; 35 species

Habitat
Freshwater rivers, streams, lakes, and ponds; other species are semiaquatic to fully terrestrial; still other species frequent estuaries and coastal waters

Conservation status
Endangered: 6 species; Vulnerable: 7 species; Lower Risk/Near Threatened: 14 species

Distribution
Temperate and tropical regions of North and South America, Europe, western Asia, and northern Africa

Evolution and systematics

The oldest fossils are known from the Upper Cretaceous and Paleocene of North America. These modern cryptodires are most closely related to the Geoemydidae of South America, Europe, Africa, and Asia and the Testudinidae, which also are found in North America.

Morphological and molecular evidence suggests a close relationship among western pond turtles (Actinemys marmorata), European pond turtles (Emys orbicularis), and Blanding's turtles (Emydoidea blandingii). Some researchers consider them to be members of a single genus (Emys), while others recognize them individually as the sole representatives of monotypic genera. Two subfamilies are recognized: the Emydinae (palatine excluded from the triturating surface) and the Deirochelyinae (humeropectoral sulcus excluded from the entoplastron).

Physical characteristics

There are typically eight pleurals, five vertebrals, and 24 marginals on the carapace and 12 scutes on the plastron. The seam between the posterior marginal scutes and the last vertebral overlap the pygal bone. A double articulation is found between the fifth and sixth cervical vertebrae. Most species have at least some webbing between the toes, and some species have a hinged plastron.

Bog turtles (Glyptemys muhlenbergii) attain a maximum size of 5 in (12 cm), whereas adult Gray's sliders (Trachemys venusta grayi) may reach 24 in (60 cm) or more. Males are generally smaller than females in the aquatic emydids; however, among semiaquatic and terrestrial species this may be reversed.

Distribution

These turtles are found in the lowland temperate regions of North America, North Africa, southern Turkey, the Middle East, and throughout Europe to southern Russia. They were formerly more widespread in Europe, but the Scandinavian populations were extirpated during the Pleistocene.

Habitat

This extremely diverse family is found in many habitats. They occur in abundance in most permanent freshwater rivers, streams, lakes, and ponds. One species is only found in estuaries and coastal waters, and a few species are semi-aquatic to fully terrestrial.

Behavior

Whether fully aquatic or terrestrial, most emydids have a well-developed basking habit. Some species are active year-round; others are seasonally inactive (dry season or winter). Males of many species exhibit elaborate courtship displays. Among the temperate northern species, hibernacula are generally located in well-oxygenated areas; however, painted turtles (Chrysemys picta) and Blanding's turtles are tolerant of extremely hypoxic, or low oxygen, conditions. At least two aquatic species, the chicken turtle (Deirochelys reticularia) and the western pond turtle, are known to hibernate terrestrially. The eastern box turtle (Terrapene carolina) burrows beneath leaf litter and hibernates in shallow soil where it may experience subfreezing temperatures.

Feeding ecology and diet

This family includes species that are strictly herbivorous to those that are strictly carnivorous. Hatchlings of many species are highly carnivorous, but switch to a more omnivorous diet as they mature. Some species have diverse, generalized diets and others are highly specialized. In map turtles (genus Graptemys), the females may develop huge heads with broad palates that enable them to crush large mollusks. Chicken turtles and Blanding's turtles have independently evolved a long neck with a well-developed hyoid apparatus, an elaborate bony structure that rapidly expands the throat to suck in prey items. This feeding adaptation is frequently found in piscivorous (fish-eating) turtle species.

Reproductive biology

In sexually dimorphic aquatic species, the female is larger than the male. The size difference is most extreme among species of the genus Graptemys. Mating generally occurs in the spring; however, some species may store sperm from an earlier mating for several years. The male is brightly colored and may possess long thin claws on the forelimbs that are vigorously waved before the female during courtship. A unique pattern of head bobs also may be exchanged before

the female allows the male to mount. This elaborate courtship suggests that females choose their mate. The elongate eggs, which may be flexible or brittle shelled, are generally laid in nests dug in the soil away from the water (sometimes more than 0.6 mi [1 km] away). Most species that have been investigated exhibit temperature-related sex determination.

Conservation status

Seven species are listed as Vulnerable and six as Endangered on the IUCN Red List; 14 others are listed as Lower Risk/Near Threatened. Human activities (e.g., pollution, habitat destruction, road mortality, and collecting for the pet

trade) are responsible for declines in most species. No species demonstrates the destructive effect that human exploitation may have on a turtle population better than the diamondback terrapin (Malaclemys terrapin), which once faced extinction throughout its range due to overcollection for human consumption. This turtle recovered as it fell out of favor with the wealthy.

Significance to humans

Many species are prominent in the international pet trade; the red-eared slider (Trachemys scripta elegans) has been the world's pet turtle for several decades. The hatchlings are exported by the tens of thousands from ranching operations in Louisiana. This turtle has established breeding populations throughout the world and is considered an invasive pest because it may harm native species. A few species are consumed by humans locally.

Species accounts

List of Species

Painted turtle

Chrysemys picta

subfamily

Deirochelyinae

taxonomy

Testudo picta Schneider, 1783, location unknown, although said to be England (in error). Four subspecies are recognized.

other common names

French: Chrysémydes peint; German: Zierschildkröte; Spanish: Tortuga pinta.

physical characteristics

A small- to medium-sized (maximum carapace length 10 in [25 cm]) turtle with a dark olive to black carapace. The upper and lower surfaces of the marginals are adorned with a pattern of red markings. The plastron may be plain yellow, yellow with a central pattern, or with complex designs of red and yellow. The dark head has a pattern of thin yellow lines and a distinctive yellow spot behind the eye in most sub-species. The males are smaller than the females and have long claws on the forelimbs.

distribution

This widespread species is found from southwestern British Columbia to Nova Scotia and throughout the central and southern regions of temperate North America. Disjunct populations occur in the U.S. Southwest.

habitat

Ponds, streams, slow-flowing portions of rivers and estuaries.

behavior

By absorbing solar radiation with their dark carapaces, painted turtles thermoregulate by basking on almost any exposed surface. They bask early in the morning to elevate their body temperature, forage for food, and then return to basking sites to facilitate digestion. In the northern populations, the juveniles and adults spend a majority of the winter trapped below thick ice. This species does not readily absorb oxygen from the water; therefore, it must tolerate long periods of hypoxia or anoxia. The mineralized shell buffers the accumulation of lactic acid formed under anaerobic conditions to maintain a stable blood pH through the winter. The hatchlings remain within the shallow nest chamber over the winter and may be exposed to temperatures of 10°F (−12°C) or lower. Although they tolerate freezing at high subzero temperatures (e.g., to 25°F [−4°C]), they must remain supercooled (i.e., without the tissues freezing) in order to survive colder temperatures.

feeding ecology and diet

Omnivorous, feeding upon aquatic vegetation, insects, tadpoles, small fish, and carrion.

reproductive biology

Although individual females may not reproduce every year, nesting is annual and seasonal. Courtship and mating occur in the autumn and spring, but nesting usually occurs in the spring and early summer. Females can store sperm in their oviducts for years and may not need to mate annually. The size of the elongate, flexible eggs (1.1–1.4 in [28–35 mm] long and 0.6–0.9 in [16–23 mm] wide) decreases with increasing latitude and clutch size. As many as five, but typically one or two, clutches of one to 20 eggs are deposited in nests constructed in sand or loamy soil. The eggs hatch after 72 to 80 days of incubation. This species has temperature-related sex determination, where males are produced below 82°F (28°C) and mostly females are produced at higher temperatures. Paternity analysis using DNA has shown that eggs within the same clutch are sometimes fertilized by more than one male.

conservation status

Not threatened. This species remains common, in part because it tolerates disturbance due to human activity and its reproductive output is exceptional.

significance to humans

The colorful painted turtle hatchlings and adults are often available in the international pet trade. As a result of their small size and their considerable overlap with the larger and presumably more palatable common snapping turtle (Chelydra serpentina), they are rarely eaten by humans.

Diamondback terrapin

Malaclemys terrapin

subfamily

Deirochelyinae

taxonomy

Testudo terrapin Schoepff, 1793, Philadelphia, Pennsylvania, and Long Island, New York, later restricted by Schmidt (1953, 95) to the coastal waters of Long Island. Seven subspecies are recognized.

other common names

French Malaclémyde terrapin; German: Diamantschildkröte.

physical characteristics

A small- to medium-sized turtle (maximum carapace length 9 in [24 cm]) with a rough, slightly keeled carapace and smooth speckled skin. The light brown, gray, or black carapace has raised concentric rings because the scutes are not shed each year, and new larger scutes form below. The rigid plastron varies in color from yellow to black and may have a distinctive pattern of blotches. The color of the soft skin is also quite variable, ranging from black to a light gray with black flecks. The females are much larger than the males and have larger heads with broad crushing plates. There are specialized salt glands near the eyes that excrete excess salt.

distribution

East Coast of temperate North America from southern Texas along the Gulf of Mexico and around Florida to Cape Cod, Massachusetts.

habitat

Salt marshes in brackish coastal waters and estuaries.

behavior

Normally active during the day, this species may haul out on rocks or the banks of tidal creeks to bask. Terrapins range widely while foraging for food; however, they are often found in the same small area over consecutive years. Adults hibernate communally on the muddy bottom of creek beds. In southern climates the terrapins may become active on warm winter days, but in northern populations they remain in dormancy.

feeding ecology and diet

This species is highly specialized to feed upon mollusks. The females develop especially large heads with broad jaws for crushing the shells of marine gastropods. The diet of the smaller males differs from that of the female in that they consume different size classes of gastropods and they may supplement with a variety of aquatic insects.

reproductive biology

The female is considerably larger than the male and may therefore choose her mate. In temperate regions, nesting occurs from mid-May to late July, but southern populations may nest as late as September. The females can store sperm in their oviducts for at least four years; however, fertility rates drop precipitously after the second year. The elongate eggs (1.0–1.7 in [26–42 mm] long and 0.6–1.1 in [16–27 mm] wide) have flexible shells. Two or more clutches of up to 20 eggs are deposited annually in the sandy dunes above the winter high tide mark. The eggs hatch after 61 to 104 days of incubation. Sex is dependent upon the incubation temperature; mostly males are produced from 77 to 84°F (25 to 29°C), however at 86°F (30°C) the hatchlings are all female. Most hatchlings emerge in the autumn and are presumed to hibernate aquatically, but some hatchlings may overwinter in the nest.

conservation status

This species is listed as Lower Risk/Near Threatened on the IUCN Red List. Once considered a delicacy among aristocrats, it was decimated during the early twentieth century by overcollection for human consumption. The terrapin has largely recovered; however, populations continue to be threatened by the destruction and degradation of the tidal marshes they inhabit, and many thousands are needlessly drowned in crab traps that could be made safe by a simple modification.

significance to humans

This species was once prized for its delicate flesh; however, it fortunately fell out of favor with the wealthy. It is still consumed locally and is often sold in the Asian markets of large North American cities.

Pond slider

Trachemys scripta

subfamily

Deirochelyinae

taxonomy

Testudo scripta Schoepff, 1792, location unknown, later designated as Charleston, South Carolina, by Schmidt (1953, 102). Three subspecies are recognized.

other common names

English: Red-eared slider, yellow-bellied slider.

physical characteristics

This is a medium-sized (maximum carapace length 12 in [30 cm]) turtle with a green carapace, usually marked with yellow. The upper and lower surfaces of the marginals are adorned with a pattern of yellow lines. The plastron may be plain yellow or yellow with a dark pattern, or black in melanistic males. The green head has a pattern of thin yellow lines. There is a distinctive red stripe behind the eye in one subspecies (Trachemys scripta elegans),

and a yellow blotch in another (Trachemys scripta scripta). The males are smaller than the females and have long claws on the forelimbs.

distribution

This widespread species is found from southern Michigan throughout the central, southern, and southeastern regions of temperate North America.

habitat

Ponds, streams, slow-flowing portions of rivers and estuaries.

behavior

Their daily activity consists of alternately basking to elevate body temperatures and foraging. Higher body temperatures facilitate digestion. The home range may be extensive and include aquatic habitats that can only be reached by overland migration. In northern populations the slider turtle hibernates at the bottom of the aquatic habitat beneath sheets of ice. Adults and juveniles are often frozen to death when drawdowns or extreme temperatures cause the pond to freeze solid.

feeding ecology and diet

Omnivorous, feeding upon aquatic vegetation, insects, tadpoles, small fish, and carrion.

reproductive biology

The smaller males become darker, or melanistic, as they mature. They possess long, thin claws on their forelimbs which they wave in front of the female during courtship. Several males may court a female simultaneously. Courtship and mating occur in the autumn and spring, but nesting usually occurs in the spring and early summer. Females can store sperm in their oviducts for years and do not need to mate annually. The size of the elongate, flexible eggs (1.2–1.7 in [31–43 mm] long and 0.7–1.0 in [19–26 mm] wide) is related to the size of the female. Up to five clutches of two to 23 eggs are deposited annually in dry sand, clay, or loamy soil. The female moistens the substrate with water carried in an accessory bladder as she digs. The eggs hatch after 60 to 80 days of incubation under field conditions. Although other environmental factors are known to influence the hatchling sex ratio, it is largely related to the incubation temperature; mostly males are produced from 72.5 to 80.6°F (22.5 to 27.0°C), however at 86°F (30°C) the hatchlings are all female. Even in the most northern portions of their range, hatchlings generally overwinter in the nest, where they are often exposed to subzero temperatures.

conservation status

Listed as Lower Risk/Near Threatened by the IUCN. Sliders are still quite common. This resilient species is abundant even in polluted and greatly disturbed habitats.

significance to humans

This species is widespread in the pet trade. Many thousands of red-eared slider hatchlings are produced by ranching operations in Louisiana each summer. Introduced populations occur in nearly every temperate or tropical country to which they are exported, and they may represent a threat to native species.

Spotted turtle

Clemmys guttata

subfamily

Emydinae

taxonomy

Testudo guttata Schneider, 1792, type locality not stated originally. No subspecies are recognized.

other common names

French: Clemmyde à gouttelettes;, Tortue ponctuée; German: Tropfenschildkröte.

physical characteristics

A small (maximum carapace length to 5 in [12.5 cm]) turtle with a smooth, dark carapace that is punctuated with yellow or orange spots. The upper surfaces of the skin are similarly dark and spotted. The digits are weakly webbed.

distribution

Great Lakes region from northern Illinois to southern Ontario, and the eastern United States from Maine to central Florida.

habitat

Bogs, wet meadows, and woodland streams.

behavior

Equally at home on the land or in the water, the spotted turtle migrates between habitat types throughout the year. It basks on mats of vegetation floating at the surface of the water or on tussocks of marsh grass. This species has one of the shortest activity seasons of any temperate species. Although it is active at low temperatures in early spring, by mid- to late June the spotted turtle seeks out muskrat burrows or buries itself beneath the ground to estivate until the summer heat has subsided. It is briefly active during the autumn before hibernation.

feeding ecology and diet

The spotted turtle is omnivorous, consuming a variety of animal matter (aquatic and terrestrial insects, worms, slugs, crustaceans, and tadpoles) as well as aquatic grasses and filamentous algae.

reproductive biology

Courtship behavior has been observed at low temperatures during March and April and continues through June. Several males may aggressively pursue a single female across terrestrial and aquatic portions of the habitat. After the male bites the female repeatedly on the hind limbs and tail, copulation proceeds either on land or water. Nesting generally occurs in the early morning or late evening from May to July. The size of the elongate, flexible eggs (1.0–1.3 in [25–34 mm] long and 0.6–0.7 in [16–18.5 mm] wide) is related to the carapace length of the female. Up to two clutches of one to eight eggs are deposited annually in the grass tussocks, hummocks, and sphagnum moss of the wetland or in upland nests constructed in loamy soil. The eggs hatch after 70 to 83 days of incubation. Sex is dependent upon the incubation temperature; mostly males are produced from 72.5 to 80.6°F (22.5 to 27.0°C), however at 86°F (30°C) the hatchlings are all female. Hatchlings generally emerge from the nest in the autumn, but may occasionally overwinter in the nest.

conservation status

This species is listed as Vulnerable on the IUCN Red List. It is protected by state and local laws throughout its range, but the regulations are not rigorously enforced and entire populations are often collected for the pet trade.

significance to humans

This species is popular in the international pet trade because of its small size, attractive pattern, and docile nature.

European pond turtle

Emys orbicularis

subfamily

Emydinae

taxonomy

Testudo orbicularis Linnaeus, 1758, southern Europe. About 14 subspecies are variably recognized.

other common names

None known.

physical characteristics

A small- to medium-sized (maximum carapace length to 12 in [30 cm]) turtle with a smooth, dark carapace that is punctuated with yellow spots or streaks. The upper surfaces of the skin are similarly dark and spotted. The digits are webbed and the tail is relatively long.

distribution

Northwestern Africa (Tunisia to Morocco), Europe (Portugal to Greece to Lithuania) to northern Iran, and the Aral Sea region in southern Russia.

habitat

These turtles are found in most aquatic habitats with soft bottoms and abundant vegetation, including rivers, streams, drainage canals, ponds, and marshes.

behavior

This species basks to elevate body temperature, but quickly retreats to the bottom when disturbed. It is active at low temperatures in early spring; by mid- to late June in southern portions of the range it may estivate until the summer heat has subsided. It is briefly active during the autumn before hibernation, which may last six months at the northern limits of the range.

feeding ecology and diet

The European pond turtle is predominantly carnivorous, consuming aquatic and terrestrial insects, worms, crustaceans, fish, frogs, salamanders, and tadpoles.

reproductive biology

Courtship behavior has been observed at low temperatures during March to May. The males are aggressive breeders; after biting the female repeatedly on the hind limbs and tail and bumping her with his shell, copulation proceeds either on land or water. Nesting generally occurs in the early morning or late evening from May and June. The size of the elongate, flexible eggs (1.2–1.5 in [30–39 mm] long and 0.7–0.9 in [18–22 mm] wide) is related to the carapace length of the female. Up to two clutches of three to 16 eggs are deposited annually in loamy soil. The incubation temperature determines the sex of hatchlings; mostly males are produced from 75 to 82°F (24 to 28°C), but at 86°F (30°C) nearly all the hatchlings are female. In northern habitats the eggs hatch in late summer or early autumn after an extended incubation. Hatchlings generally emerge from the nest in the autumn, but may occasionally overwinter in the nest.

conservation status

This species is listed as Lower Risk/Near Threatened on the IUCN Red List. Although they are not considered to be threatened, many European pond turtle populations must contend with the red-eared slider, an aggressive competitor that has been introduced through the pet trade.

significance to humans

This species is popular in the pet trade because it is relatively small, attractive, and docile.

Eastern box turtle

Terrapene carolina

subfamily

Emydinae

taxonomy

Testudo carolina Linnaeus, 1758, Carolina (exact location not cited). Six subspecies are recognized.

other common names

French: Tortue tabatière; Spanish: Tortuga de Carolina.

physical characteristics

This is a small- to medium-sized (up to 9 in [22 cm] maximum carapace length) turtle. The high domed shell is adorned with a variable pattern of yellow striations on a black background. The plastron has two hinges that allow it to draw both lobes against the carapace, forming a tight seal that protects the limbs from predators. The smaller males have red eyes, a concave plastron, and a long thick tail.

distribution

Southern, central, and eastern United States, northeastern Mexico, and the Yucatán Peninsula.

habitat

Woodlands, pastures, and wet meadows.

behavior

Eastern box turtles are active throughout the day, but retreat to short, temporary burrows when temperatures reach extremes of hot and cold. They bask early in the morning, forage, and then bask to improve digestion. Their activity increases after periods of rain. Although they are dependent upon available

microhabitats, their home range is generally less than 3.7 acres (1.5 ha). This species digs a shallow burrow in the soil, but in regions where hard soil prevents deep penetration and snow is transient, they may be exposed to subzero temperatures. The adults tolerate brief freezing episodes where the heart stops beating and the majority of extracellular water is ice.

feeding ecology and diet

Omnivorous, feeding on grasses, flowers, berries, insects, and earthworms.

reproductive biology

Beginning early in May, the male displays a stereotypical courtship pattern. He first circles and bites at the female's shell, occasionally bumping her with his carapace. Males may raise their head to pulsate their colorful throat. Olfactory cues and behavioral postures of the female precipitate mounting and intromission. The male may continue to bite at the head and shell of the female throughout copulation. Nesting occurs from mid-May to late July. The size of the elongate, flexible eggs (1.0–1.6 in [25–40 mm] long and 0.7–1.0 in [17–25 mm] wide) is related to the carapace length of the female. As many as five, but usually two, clutches of 1 to 11 eggs are deposited annually in flask-shaped nests constructed in sandy or loamy soil. Although incubation may be completed in as little as 57 days, the eggs generally hatch after 70 to 80 days. Sex is dependent upon the incubation temperature; mostly males are produced from 72.5 to 80.6°F (22.5 to 27.0°C), however at 83.3°F (28.5°C) the hatchlings are all female.

conservation status

This species is listed as Lower Risk/Near Threatened on the IUCN Red List. Suburban sprawl has led to localized habitat destruction; small populations are extirpated as wet meadows are filled and stands of trees are cleared for housing developments. Box turtles that migrate from declining habitats are often killed on the roadways that bisect their range.

significance to humans

The small adult size, attractive colors and patterns, and gentle disposition of this species make it a popular choice among turtle fanciers.

Resources

Books

Dodd, C. Kenneth, Jr. North American Box Turtles: A Natural History. Norman: University of Oklahoma Press, 2001.

Gibbons, J. Whitfield. Life History and Ecology of the Slider Turtle. Washington, DC: Smithsonian Institution Press, 1990.

Schmidt, Karl P. A Check List of North American Amphibians and Reptiles. 6th edition. Chicago: University of Chicago Press, 1953.

Periodicals

Buhlmann, Kurt A., and J. Whitfield Gibbons. "Terrestrial Habitat Use by Aquatic Turtles from a Seasonally Fluctuating Wetland: Implications for Wetland Conservation Boundaries." Chelonian Conservation and Biology 4 (2001): 115–127.

Costanzo, J. P., J. D. Litzgus, J. B. Iverson, and R. E. Lee.

"Cold-Hardiness and Evaporative Water Loss in Hatchling Turtles." Physiological and Biochemical Zoology 74 (2001): 510–519.

Holman, J. Alan, and Uwe Fritz. "A New Emydine Species from the Middle Miocene (Barstovian) of Nebraska, USA, with a New Generic Arrangement for the Species of Clemmys sensu McDowell (1964)." Zoologische Abhandlungen (Dresden) 51 (2001): 331–353.

Pearse, D. E., F.J. Janzen, and J. C. Avise. "Multiple Paternity, Sperm Storage, and Reproductive Success of Female and Male Painted Turtles (Chrysemys picta) in Nature." Behavioral Ecology and Sociobiology 51 (2002): 164–171.

St. Clair, R. C. "Patterns of Growth and Sexual Size Dimorphism in Two Species of Box Turtles with Environmental Sex Determination." Oecologia 115 (1998): 501–507.

Patrick J. Baker, MS