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Critterguy / Critter Field Guide / Turtles / common map turtle
Critter Field Guide: Turtles of Michigan

common map turtle
Graptemys geographica


map turtle (hatchling)
map turtle (hatchling)
Description

The map turtle has a greenish, olive, or brown carapace with a low keel and an irregular pattern of yellowish lines that suggest roadways on a map. This pattern may be obscured in older specimens. The skin on the head, neck, and legs is olive or brown with thin yellow stripes, and there is usually a small yellow spot behind each eye. The plastron is light yellow, though young specimens often have dark lines running along the scute edges. Females are bigger and have much wider heads than males.


Adult Male Carapace Length:
4 to 6.3 inches (10 to 16 cm).


Adult Female Carapace Length:
6.7 to 10.7 inches (17 to 27.2 cm).


Habitat and Habits

Map turtles live in the larger lakes, rivers, and oxbow sloughs, and they are often seen basking on emergent logs and rocks. When disturbed, these shy animals dive into the water and hide under log jams or submerged brush. Map turtles are powerful swimmers and, unlike most turtle species, will inhabit waters with fairly strong current. The wide jaws of adult females are well adapted for crushing the shells of snails, other mollusks, and crayfish. The males feed on aquatic insects and smaller mollusks. Feeding takes place under water.


map turtle (male)
map turtle (male)
Reproduction

Female map turtles dig their nest holes in sunny spots near the water, often on warm, rainy evenings, from late May to early July. One or two clutches containing from 6 to 20 elliptical eggs are produced each year. The eggs hatch after an incubation period of 65 to 80 days. The hatchlings, about 1.25 inches (3.2 cm) long, head directly for water upon emerging from the ground and can swim and dive well almost immediately. Some hatchlings may overwinter in the nest and emerge in spring.


Range and Status

Map turtles are found in the southern and western counties of the Lower Peninsula. They are common in many rivers and lakes, but some populations have been reduced or eliminated by pollution or by unthinking persons who use basking turtles as living targets for firearms. (Shooting reptiles is unlawful in Michigan.)


map turtle
map turtle
Acknowledgement

James Harding
MSU Museum
Michigan State University
East Lansing, MI 48824
(517) 353-7978
hardingj@msu.edu

© Copyright 2004. All Rights Reserved.