Eastern Mud Turtle

Kinosternon subrubrum (Bonnaterre, 1789)

eastern mud turtle
Eastern Mud Turtle, Massac Co., IL. photo by C.A. Phillips
view of the plastron of the eastern mud turtle
Massac Co., IL photo by C.A. Phillips

Key Characters: Tenth marginal scute highest; eighth and ninth marginal scutes rectangluar and of equal height; triangular pectoral scutes barely in contact; plastron hinged anterior and posterior to abdominal scute.

Similar Species: Yellow Mud Turtle, Eastern Musk Turtle. See Key to Adult Turtles of Illinois for help with identification.

Subspecies: Three subspecies are currently recognized: Mississippi Mud Murtle, K. s. hippocrepis Gray, 1855Florida Mud Turtle, K. s. steindachneri (Siebenrock, 1906); and the Eastern Mud Turtle, K. s. subrubrum.  Smith (1961) considered the Illinois specimens intergrades between Kssubrubrum and Kshippocrepis.

Description: Small (12 cm CL) turtle with dull brown carapace, scutes sometimes dark bordered. Sides of head spotted or mottled with yellow. Plastron dark brown or tan. Male has divided patch of rough scales behind knee and a larger swollen tail tipped with a claw. Hatchling tiny (2.0 – 2.5 cm CL) with a dark carapace and an orange, red, or yellow plastron bearing an extensive patch of dark pigment.

Habitat: Shallow stagnant or slow-moving temporary aquatic habitats: flatwoods, backwaters, oxbows, cypress swamps.

Natural History: Omnivorous, forages along bottom in shallows for mollusks, crustaceans, insects, and plants. Lays 2 – 5 ellipsoidal (ca. 30 x 17 mm), brittle-shelled eggs in and under debris or in burrows excavated using the front and hind limbs. Frequently found moving on land. Skorepa & Ozment (1968. Trans. Illinois St. Acad. Sci. 61:247-251) studied two populations of Ksubrubrum in Massac County over five years and found that the turtles burrowed into the mud in the bottom of drying wetlands as the water receded.

Distribution Notes: Two records are not plotted here; Garman’s record for Peoria (Peoria County) from his “A synopsis of the reptiles and amphibians of Illinois” (1892. Illinois Laboratory of Natural History Bulletin 3(13):215-388) and Hay’s record for Mt. Carmel (Wabash County) from his “A preliminary catalogue of the Amphibia and Reptilia of the state of Indiana” (1887. Cincinnati Soc. Nat. Hist. Jour. 10(2):59-69). Neither record is supported by specimens. Smith (1961) discussed these records and provisionally accepted them based on the fact that “a recently collected specimen from Calhoun County is available, and a colony of Ksubrubrum is well known in northern Indiana”. I have failed to locate the Calhoun County specimen. However, there is a specimen in the collection of Principia College (Elsah, IL) from Jersey County. This specimen (PC 404) was originally catalogued as Kflavescens, but was later identified as Ksubrubrum by John Tucker. This allows the possibility that the Calhoun and Jersey county specimens are valid, but likely transients and no established populations occur in the middle Mississippi of Illinois.

Status: Uncommon. Drainage of woodland ponds and wetlands in the southern tip of the state constitutes an important threat. Listed as a Species in Greatest Need of Conservation in the Illinois Wildlife Action Plan.

Etymology: Kinosternon – kineo (Greek) meaning move; sternon (Greek) meaning chest, breast; subrubrum – sub (Latin) meaning under, from; rubrum (Latin) meaning red.

Original Description: Bonnaterre, P.J. 1789. Tableau encyclopédique et méthodique des trois règnes de la nature, . . . Erpétologie. Panckoucke, Paris, xxviii+71 pp.

Type Specimen: Not designated.

Type Locality: Not stated.

Original Name: Testudo subrubra Bonnaterre,1789

Nomenclatural History: Originally described by Lacepede as Testudo subrubra in 1788 (Histoire Naturelle des Quadrupèdes Ovipares), but that work was considered non-binomial (and thus unavailable) by the ICZN. H. Garman (1892. A synopsis of the reptiles and amphibians of Illinois. Illinois Laboratory of Natural History Bulletin 3(13):215-388) was the first to include this species in the Illinois herpetofauna under the junior synonym Cinosternum pennsylvanicum (Gmelin, 1789).