Methods For Deterimining the Gender
of Burmese Pythons

There are several reliable methods of determining the sex of pythons and several less than reliable methods. Every method carries some risk of injury to your snakes, this risk can be minimized with experience. When in doubt, find someone who does it frequently!

Everting the Hemipenes, also known as "popping":
This is done by manually manipulating the tail of very young juvenile hatchlings and it is a fairly reliable method. The idea is to bend them dorsally in the region of the vent while at the same time putting pressure crainially on the tail just caudal to the vent - most of the time, if the snake is a male, the hemipenes will evert allowing you to visually inspect them and deem the snake a male. If you do not see hemipenes, you're likely to believe the snake is a female... and rightfully so, because if they are hatchlings, most males evert. However, care should be taken if hemipenes are not visualized to look for the tiny oviduct of the female so you can be certain you've "popped" the snake correctly and haven't just called a male a female due to poor technique.

Probing:
This the most commonly used method and is quite reliable when done by an experienced person. Probin is acomplished by passing a ball-tipped snake sexing probe caudally from the vent to penetrate the anal sac of the female, or the hemipenal area of the male. Extreme care must be taken when doing this so as to not injure the snake's genitalia - pressure can be felt in the male's sac if the probe encounters the flesh of a hemipene and it is not manuevered carefully - then you may sex out that male as a female, or push on and damage his hemipene. If you push too hard on a female you run the risk of puncturing the anal sac which can lead to pain, bleeding, sepsis and possible death. There is also often a "blind sac" type extension from the female's anal sac that stretches out the legnth of the male hemipene - and so it is important the probe you use is large enough to not penetrate this small canal or damage any tissue it may encounter. Use lots of lubricant and make certain you have the right probes. Probing is not as useful for hatchlings as other methods due to the risk of injury for the snake.

A little diagram of this:

Probing a female Burmese python:

The probe should easily pass caudally into the snake's small musk sac. When measured, this distance should equal around 3-6 ventral scales.

Probing a male Burmese python:

The probe should easily pass caudally into the snake's tail, slipping deep along side the hemipene. When measured, this distance should equal around 10-16 ventral scales.

For probing to be reliable, you need to have probes made for doin this! Good probes can be purchased @ Tongs.com.

Hydrostatic Eversion:
I think this is the most reliable method if you only have one snake and it's hard for you to find someone who really knows their probing. It's also nice if you want to be sure your snake is not injured - although a careless veterinarian can do some damage with this method if they mess up the anesthesia, or if they puncture the hemipene. The basic jist is that the animal is anesthetised (because this keeps the muscle that retracts the hemipene from fighting the eversion) and then a veterinarian injects isotonic saline into the tail below the end of where the hemipenes would be. Quite a bit of saline is needed and this creates a hydrostatic pressure that eventually forces the hemipenes out of the vent. This is a very reliable method although there is cost associated.

External Sexual Dimorphism:
This can be more reliable the more experienced you are with these animals, and the older the animal to be sexed may be - and it's basically just looking at the differences in the snake's appearances. Males are always smaller adults than the females, and they have more pronounced cloacal spurs. Males also tend to have a slightly longer looking tail. This is all rather unreliable when the snakes are immature or if you only have one gender available. Obvious sexual behavior when placed in pairs can be a fairly reliable finding if you know what to look for.

*DNA Karyotyping:
While analyzing chromosomal DNA is the most expensive method of determining the sex of anything, it is also is the most accurate and quite safe (could maybe even be done from a buccal/mouth swab)! Don't make fun of me for mentioning it, as science evolves stuff like this is getting extremely easy to do in most small diagnostic labs and will soon be more affordable than many of the other methods.

Radiology:
Radiographic contrast material can be injected into the same region you might probe and will with out a doubt, show you the anatomical structures of interest on a radiograph.

Ultrasonography:
While several sources in the literature report difficulty sexing snakes using ultrasound… I'm sort of convinced it can be done reliably if one knows what to look for. I'm doing further research on this because this could be a very promising, extremely safe, totally non-invasive and fairly inexpensive method of determining gender.