Sexing probes are used to determine the sex of snakes by searching for a male's hemipenis (one half of the hemipenes, the name for the entire reproductive organ). In a male snake, that two-pronged organ lies just behind the cloaca (vent) and extends toward the tail. It rests inside-out, like two socks laying side by side, when not in use. It's what makes adult male's tails appear thicker at their bases for the several centimetres just past their cloacas.
With an assistant holding the snake's body (with the belly facing up), a probe is inserted under the large cloacal scale in a direction pointing towards the tip of the tail, bending the tail backwards slightly makes it easier to find the cloacal opening. Use the probe to gently poke around (while slowly twirling it to facilitate forward movement) to find either opening that is just off-centre in the base of the tail.
Lubricant such as K-Y Jelly, or even just plain water, may be applied to the probe first to make it easier to insert. Angle the probe a little in various directions while probing until an opening is found, then try to slide it further toward the tail tip. Only the very slightest pressure is used when looking for the hemipene's openings. Too much pressure may puncture body tissue and cause injury.
Because of the elasticity of the hemipenes, the probe will have a slightly 'bouncy' feel if fully inserted into a male's organ. The same procedure on a female will produce a much firmer 'dead stop' as the probe encounters only a muscular wall at the base of her tail. When king snakes are probed, it is common to encounter a few drops of blood and is no cause for concern.
The illustration below shows the belly-up views of the tail regions of a male snake (top) and a female snake (bottom). The illustration shows the size & position of the male's hemipenes, and the position of a female's scent glands. The male's hemipenes are much deeper than the female's scent glands, so sexing a snake via probing should be close to 100% reliable, providing the procedure is done correctly.
If the snake is a male, the probe will slide down inside one or the other hemipenis to a depth greater than the width of the tail base. Baby corn snakes should not be probed, but if they were, the probe would reach a depth of approximately 10 - 12mm inside a male's hemipenis, but only 1 or 2mm inside a female's scent gland. An adult male corn snake that is 3 feet or longer will have a hemipenes that probes 40 - 70mm deep. By comparison, an adult female corn snake of the same size will probe only about 6 - 12mm deep.
Some sets of probes have wider ball tips as shown in the illustration, and others are simply smooth, slender rods with rounded tips, both types are precision made instruments which are safe to use on corn snakes, however, great care should be taken to use an appropriate size probe for the snake, and no probe with a tip greater than 4mm should be used, even on the largest of corn snakes.
This technique is called 'popping' because you literally 'pop' the hemipenes out of a male snake, a female will show little more than two tiny red dots instead of hemipenes. An experienced herper should be able to 'pop' baby corn snakes with a fairly high accuracy rate.
Both of these snake sexing techniques should only be carried out by experienced herpers.
Inexperienced herpers could possibly injure the snake making future breeding not possible.
If you feel confident about 'popping' your own baby snake, below are some photographs
of my husband popping one of our baby corn snakes along with some instructions.
First, hold your baby snake with it's
cloacal opening (vent) facing you.
Then slide your fingers holding the body end of the
snake closer to the vent. Support the snake by it's sides,
gently, but firm enough to hold the snake in position.
With your other hand, place your index finger under
the snakes vent, and place your thumb on the snakes
tail with the tip of your thumb about 6mm (¼ inch)
from the vent, then apply a little pressure with the ball
of your thumb, thus lifting your thumb tip off the tail
and making the tail bend slightly downward.
Now 'roll' your thumb (DON'T SLIDE) towards the vent.
When your thumb tip gets close to the vent, one or both
hemipenes should 'pop' out if you have a male snake.
This picture shows the hemipenes fully out.
If nothing pops out, try again, but move your 'popping'
thumb slightly further from the vent. If you are 'popping'
a female snake, you should see two tiny red dots appear
in place of the males hemipenes.
A baby snakes hemipenes
in a little more detail !!
Snake's reproductive organs can be damaged by applying too much pressure while popping.
It is always best to 'pop' a known male first, so you can perfect the technique.
Baby snakes often 'poop' on you when attempting to 'pop' them !!
Good luck with sexing your snake.