Glyptemys insculpta(North American) Wood Turtle

Geographic Range

Glyptemys insculpta occurs in a relatively small area of eastern Canada and the northeastern United States, from Nova Scotia and New Brunswick south through New England, Pennsylvania and northern New Jersey, to northern Virginia, and west through southern Quebec, southern Ontario, northern Michigan (northern Lower and Upper Peninsulas), northern and central Wisconsin, to eastern Minnesota; an isolated population occurs in northeastern Iowa. Within this range, this turtle is generally uncommon to rare and spottily distributed (Harding, 1997; Conant and Collins, 1998).

Habitat

Glyptemys insculpta is almost invariably found in association with moving water (streams, creeks, or rivers), although individuals in some populations may wander considerable distances away from water, especially in the warmer months. Females may be more terrestrial than males in some populations. Streams with sand or sand and gravel bottoms are preferred, but rocky stream courses are sometimes used, especially in the north-eastern portion of the range. Wood turtles are often described as a woodland species, but in some places they appear to thrive in a mosaic habitat of riparian woods, shrub or berry thickets, swamps, and open, grassy areas. Some unvegetated or sparsely vegetated patches, preferably with moist, but not saturated, sand substrate, are needed for nesting (Harding, 1991; Ernst, Lovich, and Barbour, 1994; Harding, 1997; Tuttle, 1996).

  • Aquatic Biomes
  • rivers and streams

Physical Description

Adult wood turtles have a carapace length of 16 to 25 cm (6.3 to 9.8 inches). The brownish to gray-brown carapace has a low central keel, and the scutes usually show well-defined concentric growth annuli, giving the shell a rough, "sculptured" appearance that probably gave the species its specific name (and perhaps its common name as well). In some specimens, the accumulated annuli may give each carapace scute a somewhat flattened pyramidal shape (though this character has been over-emphasized in some earlier literature). The carapaces of older specimens may be worn quite smooth. The vertebral scutes sometimes display radiating yellow streaks, or yellow pigment may be restricted to the keel. The hingeless plastron is yellow with a black blotch at the rear outer corner of each scute; there is a V-shaped notch at the tail. Plastral scutes display prominent annuli, though, as with the carapace, these can be worn smooth over time.

(Note: Counting the scute annuli, or "growth rings," can offer a reasonable estimate of age in a juvenile animal, but this method becomes increasingly unreliable as the specimen approaches and then attains maturity. In older animals, growth, and thus the formation of annuli, may essentially cease; however, counting scute annuli will usually provide a reliable minimum age for a specimen.)

The head of the Wood Turtle is black, occasionally with light dots or other markings; the scales on the upper legs are black to mottled brown, while the skin on the throat, lower neck, and on the lower surfaces of the legs can be yellow, orange, or orange-red to salmon-red, sometimes speckled with darker pigment. This skin color varies between localities, and shows some regional variation, with yellow to yellow-orange predominating in the western (Great Lakes) part of the range, and orange to reddish skin color characterizing eastern specimens (Harding, 1997).

Hatchling Wood Turtles have nearly circular carapaces that range in length from 2.8 to 3.8 cm (1.1 to 1.5 inches); their tails are nearly as long as the carapace. At hatching they are a uniform brown or gray color dorsally; the brighter juvenile and adult coloration described above is attained during the first full year of growth (Harding, 1997).

Compared to females, adult male G. insculpta tend to have wider heads and higher, more elongate and domed, carapaces; the plastron is concave (depressed) in the center, and their tails are thicker and longer, with the vent (cloacal opening) beyond the edge of the carapace when the tail is extended. Compared to males, adult females tend to have lower and wider, more flaring carapaces; the plastron is flat to slightly convex, the tail is narrower and slightly shorter, with the vent situated beneath the edge of the carapace when the tail is extended (Ernst, Lovich, and Barbour, 1994; Harding, 1997).

Reproduction

Male wood turtles form dominance hierarchies in the wild, and will often aggressively attack other males; females also exhibit aggressive behavior, which can be directed both toward males and other females. Older, larger males tend to be dominant over smaller individuals, and also have better success in fertilizing eggs (Kaufmann, 1992).

Courtship may include a mating "dance" in which the male and female face each other and swing their heads back and forth; perhaps more frequently the male simply pursues the female while nipping at her limbs and shell and then mounts her carapace. While thus positioned, the male may nip at the female's head and often thumps the female's carapace by straightening and then flexing his front limbs, and dropping his plastron onto the female's shell. Copulation usually occurs in shallow water on a sloping stream bank, though courtship may be initiated on land. Mating may occur at any time during the active season, but is probably most frequent in spring and fall, when the turtles are more aquatic.

In May or June, female wood turtles seek open, sunny nesting sites, preferring sandy banks adjacent to moving water whenever possible. The female excavates the nest with her hind feet, creating a globular cavity about 5 to 13 cm (2 to 5 inches) deep. Clutch size ranges from 3 to 18 eggs (usually 5 to 13). The eggs are carefully buried, and the females goes to considerable effort to smooth and obscure the nest site, but then departs, offering no further care to her offspring. Only one clutch is produced each year, and females may not reproduce every year (Harding, 1977, 1991, 1997).

Most wood turtle eggs never hatch; nest predation by raccoons, skunks, shrews, foxes, and other predators can typically result in high losses, sometimes approaching the entire year's reproductive effort for a turtle population when predator numbers are high. In a Michigan study, 70 to 100 percent of nests were typically lost each year, mostly to raccoons. For eggs fortunate enough to escape detection, incubation requires from 47 to 69 days, dependent mostly on temperature and moisture conditions in the nest. Hatchling G. insculpta generally emerge from their nests in late August or September and move to water. They appear not to overwinter in the nest, as occurs in some other freshwater turtle species (Ernst, Lovich, and Barbour, 1994; Harding, 1997: Tuttle, 1996).

In this species, the sex of the hatchling is independent of incubation temperature, a departure from the trend in closely related emydid species (such as Clemmys guttata and Emydoidea blandingii) in which embryonic sex differentiation is directly related to nest temperatures during the middle third of the incubation period (Ewert and Nelson, 1991).

Wood turtles in the wild usually reach sexual maturity between 14 and 20 years of age; in a Michigan study, most reproductive adults were in their third and fourth decade of life. Maximum lifespan in the wild is unknown, but can probably exceed the age of 58 obtained by a captive specimen (Ernst, Lovich, and Barbour, 1994; Harding 1991, 1997).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    5840 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    5840 days
    AnAge

Lifespan/Longevity

Behavior

Wood Turtles are diurnal animals and spend much of their active time basking, whether on emergent logs and other debris along or over waterways, or on land, while hidden in grass or shrub thickets. As a species they are well adapted for the cool-temperate climate found throughout much of their range, and individual turtles can obtain body temperatures well above the air temperature by carefully orienting their shells towards the sun while maintaining a low profile out of the wind. Basking not only facilitates thermoregulation, but also allows vitamin D synthesis, and undoubtedly helps dislodge external parasites such as leeches.

Wood Turtles hibernate in winter (October through April in northern Michigan), generally on the bottom in the shallows of streams and rivers where the water will not freeze. Terrestrial hibernation has been reported, but is apparently the exception (Ernst, Lovich, and Barbour, 1994; Harding, 1997).

Individual Wood Turtles tend to remain within a linear (stream-based) home range of about 1 to 6 hectares (2.5 to 15 acres), though some individuals may move considerably greater distances, using stream valleys as dispersal corridors. Most Wood Turtles remain in or within a short distance of moving water throughout the year, despite a tendency to move and forage terrestrially during the warmer months (Harding, 1997; Tuttle, 1996). Eighty-four percent of the New York G. insculpta artificially displaced overland less than 2 km were able to return to their home ranges, but only 17 percent of those displaced more than 2 km were able to return (Carroll and Ehrenfeld, 1978). However, a Wood Turtle displaced 8 km upstream along a river returned home in two months (Harding and Bloomer, 1979).

Wood Turtles are physically quite agile and reportedly are unusually intelligent (for turtles). One report found that Wood Turtles in the laboratory were able to learn mazes about as well as rats under similar conditions (Tinklepaugh, 1932), but many reports on Wood Turtle intelligence are anecdotal and based on the subjective opinion of the observer. Perhaps because they have evolved behavioral adaptations that allow them to move with ease between riparian aquatic habitats and wooded terrestrial habitats, Wood Turtles may appear more intelligent to a human observer than would other turtle species that are adapted for less variable habitats (Ernst, Lovich, and Barbour, 1994; Harding, pers.obs.).

Food Habits

Glyptemys insculpta is an omnivorous species that can feed both in or out of water. Natural foods reported for the species include leaves and flowers of various herbaceous and woody plants (violet, strawberry, raspberry, willow), fruits (berries), fungi, slugs, snails, worms, and insects. They are usually slow, deliberate feeders, and seem incapable of capturing fish or other fast-moving prey, though they will opportunistically consume young mice or eggs, or scavenge dead animals (Ernst, Lovich, and Barbour, 1994; Harding, 1997)

Wood Turtles in some populations are known to capture earthworms by thumping the ground with their forefeet or the front of the plastron. It is thought that the worms may mistake the vibrations caused by this thumping for the approach of a mole or perhaps the advent of a hard rain, and thus come to the surface, only to be grabbed by the hungry turtle (Harding and Bloomer, 1979; Kaufmann, et al., 1989; Ernst, Lovich, and Barbour, 1994).

  • Animal Foods
  • eggs
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms
  • aquatic crustaceans
  • Plant Foods
  • leaves
  • roots and tubers
  • fruit
  • flowers
  • Other Foods
  • fungus

Economic Importance for Humans: Positive

Wood Turtles were once harvested extensively for human food (in the east) and for the biological supply trade (especially in the western Great Lakes area), and in the last few decades they have been mercilessly exploited for the pet trade range-wide. None of these activities are sustainable in the long-term; most populations of Wood Turtles are now greatly reduced from former numbers, and many have been totally extirpated (Harding, 1991, 1997).

  • Positive Impacts
  • pet trade
  • food
  • body parts are source of valuable material
  • research and education

Economic Importance for Humans: Negative

This species is harmless to human interests and values.

Conservation Status

Glyptemys insculpta displays a number of life history traits that make it especially vulnerable to exploitation and habitat alteration by humans. In this and many other turtle and tortoise species, low reproductive rates (low clutch size and/or high nest and hatchling mortality) and delayed sexual maturity are normally balanced by relatively high survivorship of older juveniles and adults, and a long adult reproductive lifespan. It has been demonstrated that such species have virtually no harvestable surplus in their populations (assuming the desirability of population stability), and any factor (natural or human-caused) which reduces the normally high survivorship of older juveniles and mature adults will result in a declining or even extirpated population. In addition, these turtle populations will predictably be very slow in recovering from any factor which significantly reduces numbers of mature individuals. The Wood Turtle may be equally, or even more vulnerable than certain other well-studied turtle species (such as Emydoidea blandingii) in this regard (Congdon et al., 1993; Harding, 1991, and unpubl. data).

Direct removal by humans is the primary threat to the species in some portions of the Wood Turtle's range. Removal can take the form of road mortality, shooting of basking turtles by vandals, commercial poaching for the pet trade, or just incidental collection by stream-based recreationists such as canoeists and fishermen. In one study (Garber and Burger, 1995), a previously unexploited population of Wood Turtles declined to virtual extirpation within a decade of being exposed to human recreationists. Glyptemys insculpta is legally protected from commercial collecting practically range-wide at present, and collection for personal use is at least regulated, if not prohibited, by most of the states and provinces where it occurs.

Wood Turtles have also suffered greatly from habitat loss and degradation. While the species seems somewhat tolerant of modest timber harvest and agricultural activity in its habitat, intensive forestry, farming, or industrial or residential development in the riparian zone can severely impact Wood Turtles. Intensive, mechanized agriculture can result in maiming and deaths of Wood Turtles due to impacts from farm machinery (Saumure and Bider, 1998). Certain fish management practices that involve removal ("stabilization") of sand bank nesting sites along northern rivers is a relatively recent threat that can reduce reproductive opportunities for this and other turtle species. An additional threat is the recent increase in numbers of "human-subsidized" predators, particularly raccoons (Procyon lotor), which not only destroy turtle eggs and hatchlings, but can also kill or maim adult turtles (Harding, 1985; 1991, 1997, pers.obs.).

The long-term future for this species is bleak unless its riparian habitats are protected and the animals themselves are left undisturbed. Wood turtles are listed as vulnerable by the IUCN and special concern in the state of Michigan, and they are in CITES appendix II.

Other Comments

Wood Turtles had a more southerly distribution during the Late Pleistocene ("ice age"), with fossils being described from Tennessee and Georgia (Ernst, Lovich, and Barbour, 1994).

The oldest fossil Wood Turtle appears to be a nearly complete shell of an adult male specimen found in late Hemphillian deposits (late Miocene epoch) in Nebraska. This fossil, which is approximately 6 million year old, will be described by its discoverer, Mr. Shane Tucker, and Dr. Michael Voorhies of the University of Nebraska (Voorhies, pers. comm., June 2000).

The relationships of the Wood Turtle to its relatives in the subfamily emydinae (in the genera Clemmys, Emys, Emydoidea, and Terrapene) have been recently studied; the genus Clemmys, as long suspected, was found to be paraphyletic (Bickham et al., 1996; Burke et al., 1996; Feldman and Parham, 2001). According to the latest published revisions, the Wood Turtle will now be combined with its closest relative, the Bog turtle (Clemmys muhlenbergii), in the genus Glyptemys; the correct scientific names for these turtles are now Glyptemys insculpta and Glyptemys muhlenbergii, respectively, although it will predictably take some time before the new combinations are universally used and recognized. The Spotted Turtle, Clemmys guttata, is the only species remaining in the genus Clemmys (Holman and Fritz, 2001; Feldman and Parham, 2002).

Hybrids between the Wood Turtle and the Blanding's turtle, Emydoidea blandingii, have recently been described (Harding, 1999).

Contributors

David Armitage (editor), Animal Diversity Web.

James Harding (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carrion

flesh of dead animals.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

solitary

lives alone

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

References

Bickham, J., T. Lamb, P. Minx, J. Patton. 1996. Molecular systematics of the genus *Clemmys* and the intergeneric relationships of emydid turtles. Herpetologica, 52(1): 89-97.

Burke, R., T. Leuteritz, A. Wolf. 1996. Phylogenetic relationships of emydine turtles. Herpetologica, 52(4): 572-584.

Carroll, T., D. Ehrenfeld. 1978. Intermediate-range homing in the wood turtle, *Clemmys insculpta*. Copeia, 1978: 117-126.

Conant, R., J. Collins. 1998. A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Third Ed., Expanded. Boston and New York: Houghton Mifflin.

Congdon, J., A. Dunham, R. van Loben Sels. 1993. Delayed sexual maturity and demographics of Blanding's Turtles (*Emydoidea blandingii*): Implications for conservation and management of long-lived organisms. Conserv. Biol., 7(4): 826-833.

Ernst, C., J. Lovich, R. Barbour. 1994. Turtles of the United States and Canada. Washington, D.C.: Smithsonian Institution Press.

Ewert, M., C. Nelson. 1991. Sex determination in turtles: Diverse patterns and some possible adaptive values. Copeia, 1991: 50-69.

Feldman, C., J. Parham. 2002. A molecular phylogeny for emydine turtles: taxonomic revision and the evolution of shell kinesis. Molecular Phylogenetics and Evolution, 22(3): 388-398.

Feldman, C., J. Parham. 2001. Molecular systematics of emydine turtles.. Chelonian Conservation and Biology, 4(1): 194-198.

Garber, S., J. Burger. 1995. A 20-year study documenting the relationship between turtle decline and human recreation. Ecological Applications, 5(4): 1151-1162.

Harding, J. 1985. Life History Notes: *Clemmys insculpta* (Predation and Mutilation). Herpetol. Rev. (SSAR), 16(1): 30.

Harding, J. 1999. Life History Notes: *Clemmys insculpta* and *Emydoidea blandingii*. Hybridization.. Herpetol. Rev. (SSAR), 30 (4): 225-226.

Harding, J. 1977. Record egg clutches for *Clemmys insculpta*. Herpetol. Rev. (SSAR), 8(2): 34.

Harding, J., T. Bloomer. 1979. The wood turtle, *Clemmys insculpta*, a natural history.. HERP: Bull. New York Herp. Soc., 15(1): 9-26.

Harding, J. 1991. A twenty year wood turtle study in Michigan: implications for conservation. Chapman University, Orange, California: In: Proceedings of the First International Symposium on Turtles and Tortoises: Conservation and Captive Husbandry.

Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: University of Michigan Press.

Holman, J., U. Fritz. 2001. 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) (Reptilia: Testudines: Emydidae). Zoologische Abhandlungen Staatliches Museum für Tierkunde Dresden, 51: 331-354.

Kaufmann, J. 1992. The social behavior of wood turtles, *Clemmys insculpta*, in central Pennsylvania. Herpetol. Monogr., 6: 1-25.

Kaufmann, J., J. Harding, K. Brewster. 1989. Worm stomping by wood turtles revisited.. Bull. Chicago Herp. Soc., 24: 125-126.

Saumure, R., J. Bider. 1998. Impact of agricultural development on a population of Wood Turtles (Clemmys insculpta) in southern Quebec, Canada. Chelonian Conservation and Biology, 3(1): 37-45.

Tinklepaugh, O. 1932. Maze learning of a turtle. Journ. Comp. Psych., 13: 201-206.

Tuttle, S. 1996. Master of Science Thesis: Ecology and Natural History of the Wood Turtle (*Clemmys insculpta*) in Southern New Hampshire. Keene, New Hampshire: Antioch New England Graduate School, Antioch University.