Physical characteristics in mature box turtles that may indicate gender are the shape of the bottom of the shell, the thickness of the tail, the length of the claws, the color of the eyes and the location of the anus. The bottom of the shell is normally curved inward on males and flat or curved outward on females.
The tail of a male turtle is generally thicker at the base than that of a female, and the front and back claws are longer for males as well. Males also may have an orange or red tinge to their eyes compared to females whose eyes are generally brown. Finally, the anus on mature male turtles is located beyond the edge of the shell, whereas for females it is normally hidden.
Because the sexual organs of box turtles are located inside the shell, it is extremely difficult to tell the gender of a very young turtle. It may take up to four years for a turtle to reach sexual maturity and then another 16 years before it reaches adulthood. The lifespan of a box turtle is very long. For example, the eastern box turtle can live up to 40 years in the wild and 100 years or more in captivity.