Identification: Kinosternon subrubrum is a small kinosternid (mud turtle) with a carapace (upper shell) length of 70-125 mm (2.75-4.92 in) (Iverson, 1977; Ernst et al., 1994; Conant and Collins, 1998). Unlike the kinosternid genus Sternotherus, the plastron (lower shell) is relatively large and has two movable hinges rather than one (Conant and Collins, 1998). The color of the domed, smooth carapace can be brown, olive, yellowish, or black; in juveniles the carapace can have three longitudinal keels (raised ridges) (Iverson, 1977; Conant and Collins, 1998). The head and neck are generally brown with a variety of lighter colored stripes or mottling (Iverson, 1977). Unlike other species ofKinosternon, the ninth marginal scute (plate or lamina) does not extend dorsally, and the first vertebral scute does not contact the second marginal (Iverson, 1977; Powell et al., 1998).
http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=1267 Revision Date: 10/28/2009
PHYSICAL DESCRIPTION: This is a small turtle with a smooth, oval carapace generally measuring between 78-123mm in length (VA maximum=123mm). There may be a weak keel in some individuals and the carapace is usually flattened dorsally. It is usually darkly colored (brown/olive/black) with no markings. Scute numbers are as follows: 11 marginals on each side, 4 pleurals on each side and 5 vertebrals *10760,11624*. The plastron is relatively large (82-94% of carapace length) with 2 obvious hinges (hinges not developed in young). Length can be anywhere from 64-108mm). Maximum known length in VA is 109mm. It may be brown or yellow with brown smudging. There are 11 plastral scutes *10760*. Skin is darkly colored (brown,gray,or black). Only markings are on the head and are variably patterned in yellow or white *10760*. Adults weigh between 88-263g with 263 being the max known weight in VA *10760*. Females are slightly larger than males but not significantly. Males have longer tails with the cloacal opening extending past the edge of the carapace. They also have patches of raised scales behind the knee and thighs. Both have spines on the end of their tails *10760*. Hatchlings are quite different than the adults. They have 3 keels on the shell and both carapace and skin is black witha orange spot in each marginal scute. The head has light markings. Plastron is orange-red with a black splotch covering much of the scutes. They also have no plastral hinges. At hatching mud turtles weigh 2-3g and have a carapace length of 21-24mm and a plastral length of 17-20mm *10760*. May be confused with stinkpots (Sternotherus odoratus) but stinkpots have exposed skin in between the plastral scutes and only one plastral hinge. Kinosternon baurii have distinct head markings (2 yellow stripes) and may have some light marking on the shell.
REPRODUCTION: Mating usually occurs between mid-March through May. Nesting occurs shortly thereafter from March 31-June 22. Nesting usually occurs after a rain, and the nest is generally a pit 7-12cm deep dug in the dirt and then covered with dirt, though they may deposit eggs under a board, or on open ground. Between two and five eggs are normally laid. Incubation in the lab took 87-104 days and there is evidence that suggests that many hatchlings overwinter in the nest. One or more clutches are laid per year. Most turtle reached sexual maturity between 70-80mm carapace length *10760*.
BEHAVIOR: This is a bottom crawler but is also a good swimmer *1038*. They are quite terrestrial also in the early morning or early evening *1027*. When the habitat dries this species burrows on land and aestivates *2988,11624*. The peak of egg laying is in June. The female selects a rather dry spot to lay the eggs, and digs a slanting hole with the hind feet. It lays the eggs and packs dirt tightly over them with the hind feet *1008*. The nest is a semicircular cavity from 3 to 5 inches deep entering the ground at a 30 degree angle *1027*. Sandy, loamy soils are preferred but piles of vegetable debris are also used *2988*. The young hatch in September, and winter in the nest or the eggs overwinter to hatch in April *1008,11624*. This species spends the winter in mud below the frost line, many select an area out of the water to hibernate, they emerge sometime in late March or early April *1008*. They may also hibernate in dead wood *1027*, and can be seen basking at times on submerged brush or on the shore but not often *2988*. They are omnivores, eating insects, crayfish, seeds and various mollusks. They are most active from March to November in Virginia *10760*.
POPULATION PARAMETERS: The sex ratio is 2:5, male to female *2988*. Survivorship for one population in South Carolina was 89% for males, 88% for females and 26% for juveniles. They can live to be up to 30 years old *10760*.
AQUATIC/TERRESTRIAL ASSOCIATIONS: The predators of adults are rodents and predators of juveniles are blue crabs, gars, water snake, hognose snake, cottonmouths and crows. Predators of the eggs include king snakes, opossums, weasels, skunks and raccoons *2988*. Large deep bodies of water are avoided and they prefer slow-moving shallow water with lots of organic matter *10760*.
Information sourced from: Virginia Department of Game and Inland Fisheries