If you want to keep more than one box turtle, it’s a good idea to know the sex of each animal. This is because males can be aggressive toward each other when housed together. They’re also aggressive toward females when they want to mate.

Unless you plan to breed them, it’s best to house males and females separately. And, of course, if you do plan to breed them you’ll want to be sure you have at least one of each!

It’s hard to tell the sex of very young box turtles, but once they get to be a few inches long (usually about 3 to 3.5 inches), you can start to see the differences between the sexes.

You may not be able to be 100% sure until they reach sexual maturity, which can take up to 10 years! Although it’s usually closer to 5-7 years, and captive males may mature in as few as four years.

In general, here are characteristics to look for when trying to tell the sex of box turtles:

• Males are often bigger than females of the same species. But this is not really a very good characteristic to use, since young males will be smaller than fully adult females. Also, in T. ornata (Western/Ornate box turtles) it is not uncommon for the female to be bigger than males of the same age.
• Males are usually more colorful than the females, especially the Eastern subspecies. Often the coloration differences are more obvious in a sexually mature male. For example:
  • Males often have bright red, pink or orange eyes. Females tend to have brown eyes, and when she does have red eyes, it’s a darker red than the males. The Florida box turtle doesn’t show this difference in eye color.
  • Male ornates often have a greenish or yellowish head. Females’ heads are usually brown.
  • Male three-toed box turtles sometimes have a dark red head.

• Males have longer, thicker tails than females. The male’s vent (opening to the cloaca) is farther away from his body than the female’s. This makes mating easier.
• Eastern box turtle males also have another feature that makes mating easier. The plastron has an indentation near the tail. The female’s plastron is flat. Ornate males do not have an obvious indentation, although some animals have a slight concavity. The indentation may or may not be present in three-toeds.
• The hind claws of a male box turtle are usually shorter, thicker and more curved than those of a female. In ornate males, the first toe on the hind leg turns in.
• You can also recognize a male if you see him “fanning.” This is a display of his penis, usually in water or wet grass. The organ looks kind of like a dark bluish/purplish flower.

This list is not perfect, and identifying one characteristic is not enough to be sure if you have a male or female. The characteristics can vary some between subspecies. Or you may have an animal where the characteristic you’re looking at isn’t obvious. It’s best to look at several characteristics before deciding if your turtle is a boy or a girl.

Also, most of these characteristics rely on differences between males and females. If you don’t have two animals to compare, it can be especially hard to tell what you’re looking at.

Many times the only way to be 100% positive is if you have two turtles that are mating … but even then you may not be absolutely positive the one on the bottom is female, because males will try to mount other males. Eggs are, of course, a sure sign you have a girl.

.