Last Updated: 30 June 2009

Sexing probes are used to determine the sex of snakes by searching for a male’s hemipenis (one half of a 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 males’ tails appear thicker at their bases for the several inches 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 scute (scale) in a direction pointing towards the tail. Bending the tail backwards slightly makes it easier to find the cloaca. Use the probe to gently poke around (while slowly twirling it to facilitate forward movement) to find either opening that’s just off-center in the tail’s base. 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 hemipenes’ 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 picture below shows the ‘belly-up’ views of the tail regions of a female (top) and male (bottom), including an x-ray view of where the hemipenes of a male is situated. Females have small pockets / scent glands in their tails, but they’re never nearly as deep as the hemipenes of males.

If the snake is a male, the probe will slide down into one or the other hemipenis to a depth more than the width of the tail base. On a baby corn snake, for instance, this depth would be about 3/8 – 1/2 of an inch. It will barely penetrate (only 1/16 – 1/8 of an inch) into the scent glands on a baby female corn snake. An adult male corn snake that is 3 feet or longer will have a hemipenes that probes 2 – 3 inches deep. By comparison, an adult female corn snake will probe only about 1/4-inch deep.

Some sets of probes have wider ball tips as shown in the diagram, and others are simply smooth, slender rods with rounded tips. The three piece sets we usually sell look very simple, but they are precisely made instruments. Use the thinnest one for snakes up to about 15 inches in length, and the thickest one for snakes over 30 inches. Probe sets with longer, stiffer individual probes will work too, though no probe over 1/16-inch thick should be used on corn snakes.