Identifying Monitor Lizards: Sex Determination Techniques And Tricks

Monitor lizards, scientifically known as Varanus, are native to Africa, Asia, and Oceania, with about 80 species recognised. While they are fascinating creatures, it is challenging to determine their sex as there is often a lack of external differences between the sexes. However, there are some methods and observable clues that can help with sexing these lizards. Sexing monitor lizards is important for understanding their behaviours and identifying possible reproductive-related diseases. This article will explore the different approaches to determining the sex of monitor lizards, including visual clues, anatomical differences, and experimental techniques.

Look for hemipenal bulges at the base of the tail

To identify the sex of a lizard, one method is to look for hemipenal bulges at the base of the tail. This is a common way to determine the sex of a lizard, as male lizards have two hemipenes (the equivalent of a penis) at the base of their tail. These are located on either side of the cloaca, and run towards the tail tip for a short distance.

The hemipenes are usually tucked away and are not visible unless exposed. They are small, moist, pink, fleshy tubes, and are used for mating. They are located underneath the lizard's cloaca, appearing as two small bulges. The bulges, along with the presence of large femoral pores, are often characteristics that indicate the lizard is male.

It is important to note that this method of sexing a lizard can be challenging and is not always accurate. As lizards age, complications can arise, and it can be difficult to distinguish between the hemipenes and the scent glands found in female lizards. Additionally, some male lizards may not have hemipenal ossification, making it harder to identify their sex through this method.

Therefore, while looking for hemipenal bulges at the base of the tail can be a helpful indicator of a lizard's sex, it is not always definitive, and other methods such as radiography, ultrasound, or DNA technology may be needed to confirm the sex of the lizard.

Check the size of the lizard's head

Monitor lizards are sexually dimorphic, meaning males and females exhibit differences in characteristics such as size, shape, and appearance. One of the most notable ways to distinguish the sex of a monitor lizard is by checking the size of its head.

Males of many lizard species, including monitor lizards, tend to have bigger and bulkier heads compared to females. This larger head size is an adaptation for territorial combat, as males use their heads for biting and wrestling other males when competing for territory and mates. Therefore, if you observe a monitor lizard with a large head, it is likely to be a male.

In addition to head size, there are other physical traits that can provide clues about the sex of a monitor lizard. Mature male monitor lizards are usually larger in overall size and have wider tail bases compared to females. However, these differences can be challenging to discern without having a lizard of the opposite sex for comparison or knowing the age of the animal.

It is worth noting that sex determination in monitor lizards can be difficult, and visual clues may not always be reliable. For more accurate sexing, advanced methods such as endoscopic examination, X-rays, or ultrasound may be required, which should only be performed by qualified veterinarians to avoid causing harm to the lizards.

Observe the lizard's colouration

Colouration is a key indicator of sex in many lizards, including monitor lizards. Male lizards tend to be more brightly coloured than females, and this is true of the western fence lizard, or bluebelly, which is common in the Bay Area. Male bluebellies have bright blue throats and blue undersides with a dark median stripe, as well as bright yellow or orange colouration under their rear limbs. Females and juveniles have some colour, but it is much more subtle.

The colouration of male lizards is often indicative of good health, as lizards with internal pathogens tend to be duller in hue. The bright colours of male lizards are used to attract females and drive off rivals.

In many monitor species, the males often have larger heads and wider tail bases than females. The male lizards also tend to be larger overall. However, these differences are often subtle and may not be discernible without a lizard of the opposite sex to compare it to.

The colour of a lizard's blood vessels can also be used to determine its sex. This method involves placing a bright light source against the tail base in a dark room and is effective in species that are lighter in colour with a thin tail.

Determining the sex of a lizard is critical for understanding its behaviour and possible reproductive diseases. For example, males can develop issues with hemipenes, while females can experience dystocia (difficulty giving birth) and egg retention.

Look for anatomical features like spikes, horns and dewlaps

Determining the sex of a lizard can be challenging, as there is often a lack of external differences between the sexes. However, one way to differentiate between male and female lizards is to look for anatomical features like spikes, horns, and dewlaps (flaps of skin on the throat). These "decorations" are typically only found on male lizards, as they are used to defend territory and attract mates.

One example of a lizard species with noticeable anatomical features is the green iguana (Iguana iguana). Male green iguanas have extremely large "jowls" at the bottom of their mouths and throats, as well as longer dorsal spikes, compared to females. Male chameleons also have elaborate head ornamentation, such as horns, crests, and plates, which are not present in female chameleons.

In addition to spikes, horns, and dewlaps, male lizards may also have other anatomical features that differ from those of females. For example, males of some lizard species may have visible bulges from the hemipenes at the base of their tails or enlarged femoral pores on the ventral region of their legs. These femoral pores are used to secrete pheromones, and are typically larger in males than in females.

It is important to note that not all lizard species exhibit the same level of sexual dimorphism. Some species may have more subtle differences between males and females, or the differences may only be noticeable during certain behaviours, such as mating displays. Therefore, it may be necessary to use other methods, such as radiography or DNA technology, to determine the sex of a lizard with certainty.

Examine the back legs for femoral pores

Femoral pores are openings of follicular glands located on the underside of a lizard's thighs, close to the anal opening. They are used to secrete pheromones, which are used to attract mates and mark territory.

Femoral pores are present in male and female monitor lizards, but they are usually more prominent in males. The pores appear as a series of pits or holes within a row of scales on the inside of the thigh.

When examining the back legs of a monitor lizard, look for these small raised bumps. In male lizards, the femoral pores will be more noticeable and may appear larger.

It is important to note that not all reptiles have femoral pores. Some lizard species, such as those in the Anguidae, Chamaeleonidae, and Varanidae families, do not have these pores.

Additionally, the number of femoral pores can vary significantly between species. For example, male lizards in the Lacertidae family can have anywhere from zero to 32 pores per limb.

The size of the femoral pores can also change with the season, as they may increase in size during the mating season when more secretions are produced.

By examining the back legs for femoral pores, you can gain important information about the sex of a monitor lizard.

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