Adult males are very easily distinguishable from adult females. The males develop a rather prominent hemipenile
bulge just behind their vent. This bulge may begin developing at around 5 months, but often it may take longer
to be visible.
Earlier in their lifespans, however, they are a bit more difficult to tell apart. A juvenile male can be spotted by looking at the ventral (bottom) side of their rear legs. Sometimes, with the naked eye, a line of very small pre-anal pores can be seen. Sometimes, for younger animals, a jeweler's loupe of 10x or stronger can be used to determine whether pores exist or not.
I prefer to make use of the cylindrical-type loupes
which can be held in the eye socket with no hands, to give you two free hands to hold the gecko.
Females will show no true pores - however, at times, females have been known to show dented-looking scales
that might be confused for pores. Keep in mind that very young
geckos under six grams may be difficult to sex, even using a jeweler's loupe, though some breeders
have become adept at seeing pores visible on even a four-gram gecko.
In the breeder/vendor world, females are generally a bit more expensive than males. This is because one male may serve as a mate for three or four females, and more than one male in a single enclosure may lead to fighting.
A word of caution: When you are planning to purchase a gecko of a certain gender, it is a good idea to procure a sex guarantee from the vendor, if possible. While most animal vendors are honest, some have been known to raise the price on an animal proclaiming it a "female," only to have the animal prove male once you've brought it home. Other vendors prefer to sell animals as "unsexed," which means they don't guarantee the sex, and you take what you get.
Adult females also may have a bit of a fatty deposit around the vent area, which may give the impression
of a small hemipenile bulge. It is for this reason that I prefer to rely on loupes and other magnification.
(If you have a strong enough camera lens, you can try taking a photo of the gecko's underside and zooming in
on the pre-anal area in a photo editor.)
When raising juvenile geckos together, it is best to remove males from an enclosure to help prevent premature breeding as well as fighting. Separation should be done at about the time a gecko's hemipenile bulge become visible, if not before.
You may notice that your gecko has a small whitish bump on either side of its vent. These are the cloacal spurs.
Both males and females have them; they are thought to be used in mating to help the male align himself with the female.
Some breeders insist that you can tell a male from a female by the size of the spurs, as males tend to have
larger spurs than the female. However, this is not always the case - I have at least one female who has larger spurs
than a male of the same size. I am personally a bit wary about breeders who insist that they know whether a
gecko is male or female from the spur size alone.
