Determining Reptile Gender

The relationship that develops between humans and pets does not recognize many boundaries. We realize the power of the human-animal bond and strive to provide pet owner with the knowledge and support required to care for their pet so that it will be rewarding. The most common question asked by a prospective new pet owner is: What is the sex (gender) of the animal?

Humans have long had a desire to name their pets, which is the first step to establishing the human-animal bond. Yet nothing is more disheartening to a pet owner than to find out that the pet they have been calling Brutus should be more appropriately named Beulah.

Anatomy Lesson
Gender determination in reptiles requires some background knowledge of reptile anatomy. Male snakes and lizards have hemipenes, paired copulatory organs, whereas chelonians, tortoises, terrapins and turtles have a singular penis. The copulatory organs of the snake and lizard are located in the base of the tail and the copulatory organ of the chelonian is located cranial (toward the head) to the vent. The methods to differentiate gender vary from group to group, even though they may share a similar type of reproductive organ.

The most common way to differentiate gender in snakes is to use a commercial probe set. The probe is gently inserted into the vent by the veterinarian and directed laterally, off-midline, in the direction of the tail. The probe will travel deeper in the male - greater than four scale lengths - than in the female - less than three to four scale lengths. The tail of the male snake is often wider and longer than the female's tail. Some herpetoculturists claim that they can determine the gender of a python based on the size of their spurs - the claws located at the level of the vent. However this technique is not accurate. Juvenile snakes can be difficult to probe because of their small size. Experienced handlers may attempt to evert the hemipenes of a juvenile male snake using their thumb or finger. However, excessive pressure can result in damage, and this technique should only be attempted by individuals with experience.

Visual Clues
Although male lizards have reproductive organs similar to snakes, they cannot be probed with the same degree of accuracy. The determination of gender in lizards is often based on sexually dimorphic characteristics - obvious external differences. Male chameleons such as the panther chameleon, often have more colorful skin patterns than females, or, as seen in the Jackson's chameleon, they possess ornate horns. In certain species of lizards, males possess specialized scale patterns. The adult male green iguana develops specialized femoral pores, located on their inner thighs that produce a waxy substance to mark their territory. These pores become well-developed in the male after approximately 8 to 10 months of age. Many of the different species of male geckos, including the leopard gecko, possess pre-vent pores. Male lizards may also be differentiated from females by the presence of hemipenal bulges in the base of the tail, which become readily apparent as the animal matures.

There are a number of different techniques used to determine the gender of a chelonian. Male tortoises often have an indentation in the middle of their plastron, bottom of the shell, which enables them to mount a female. In the Eastern box turtles, Terrapene carolina, the iris color in the female is often amber, while in the male it is red. Red-ear slider, Trachemys scripta elegans, males are much smaller than females and develop long front claws. In cases where the determination of gender cannot be made based upon sexually dimorphic characteristics, the location of the vent can be used. The vent of a male chelonian will extend, beyond the length of the carapace, with the total tail length being longer than that of a female.

These techniques described to determine the gender of a reptile will work in most cases, although there are exceptions.

This article was written by Mark A. Mitchell, DVM and was published in Pet Business in March 2000.