Sexing a turtle really isn't all that hard, once you know what features to look for. There are a number of simple checks you can perform to determine which gender your turtle belongs to:
Look at your turtle's plastron.
Of course, you knew that your shelled friend's plastron is its under shell, didn't you? As a rule, male turtles have a concave (inward) curving shell, whilst female turtle have a slightly convex (outward) or flat shell. This difference is all about sex: the female wouldn't have room for all those eggs with a concave shell; and amorous male turtles would slide off their potential mates if their under shell was curved outwards.
- Look deep into your reptile's eyes.
Male turtles tend to have red eyes, whilst female turtles generally have brown eyes. However, be warned: some ladies have red eyes (in particular box turtles), and some males have brown eyes. Spotted turtle ladies have orange eyes and yellow chins.
- Examine the location of the uhh, bum hole.
Now, now, don't be shy. A male turtle's anus is located past the carapacial rim, otherwise known as the end of the shell. Girl turtles, on the other hand, keep their bum-holes before their shell's rim, to preserve their modesty, like a lady should.
- Check the length of your specimen's claws
Amongst the turtle community, longer claws just scream success and power, so male turtles have larger, longer claws than their female counterparts, in order to attract mates. If you're a turtle voyeur, you might spot a hopeful male stroking a female's cheek. This is the height of turtle seduction.
Of course, there's only so much you can say with any certainty, until your turtle either mounts a lady turtle or starts laying little turtle eggs, but that's life, I'm afraid.