Most lizards can be sexed by flipping them over and examining the base of the tail, where males show two distinct bulges that females lack. Beyond that single clue, several other physical markers, from pore size to body proportions, make identification reliable once you know what to look for. The catch is that many of these features only become visible after a lizard reaches a certain size or age, so very young animals can be difficult to sex with confidence.
Hemipenal Bulges at the Tail Base
The most universal method for sexing lizards is checking for hemipenal bulges. Male lizards have paired reproductive organs called hemipenes, which are stored inverted inside the base of the tail. Because they take up physical space, they create two visible swellings on the underside of the tail, just behind the vent (the single opening where the tail meets the body). Females have a flat, smooth profile in that same area.
To check, gently turn your lizard over and look at the tail immediately past the vent. On a male, you’ll see two oval or rounded bumps, one on each side of the tail’s midline. On a female, the tail tapers smoothly from the body with no bulging. This works across most lizard species, from geckos to bearded dragons to monitors, though it’s easiest to see in adults.
Femoral and Preanal Pores
Many lizard families, including iguanas, bearded dragons, and geckos, have small gland openings on the underside of the thighs or just in front of the vent. These are called femoral pores (on the thighs) and preanal pores (near the vent). Both sexes can have them, but males’ pores are noticeably larger, darker, and more pronounced. During breeding season, male pores often produce a waxy or waxy-looking secretion that can appear as small plugs or raised bumps.
In iguanas, males produce visible waxy plugs along the inside of their thighs that are hard to miss. Females have the same pores, but they’re smaller and produce little to no secretion. In some gecko species, only males have preanal pores at all, appearing as a V-shaped or straight row of tiny dark dots just ahead of the vent. This pore activity is driven by male hormones, so the difference becomes more dramatic as the lizard matures and especially during breeding season.
Species-Specific Markers
Leopard Geckos
Leopard geckos are one of the most commonly sexed pet lizards, and the process is straightforward once they reach 5 to 6 inches in length. Turn the gecko over and inspect the area around the vent. Males have a clear row of preanal pores, visible as small dots across the underside between the back legs, plus two oval hemipenal bulges behind the vent. Females lack both features entirely, making this one of the more clear-cut species to identify.
Veiled Chameleons
Veiled chameleons can be sexed from birth using a feature called tarsal spurs. Males hatch with a small, prominent bony spur on each back foot, right at the heel. These spurs are obvious and hard to miss. Females either have completely flat back feet or, at most, a very small flap of skin where the spur would be. Males also develop a taller casque (the helmet-like crest on the head) and more vivid coloration as they grow.
Bearded Dragons
Bearded dragons are sexed primarily by the hemipenal bulge method. Gently lift the tail upward at about a 90-degree angle while supporting the body, and look at the base of the tail from behind. Males show two distinct raised bumps on either side of the tail’s center. Females show either one central bump or a completely smooth profile. Many keepers also use a flashlight held against the top of the tail base: the light silhouettes the hemipenes inside, making them visible as two dark shadows in males.
Body Size and Color Differences
In many species, males and females differ in overall size, head width, or coloration, though these differences are less reliable than anatomical checks. Male lizards in many species develop broader heads relative to their body, more vivid coloring, and larger overall body size. In species like green anoles, males are typically larger and have a brightly colored dewlap (throat fan) that they extend during displays, while females have a smaller or absent dewlap.
Size-based differences usually don’t become apparent until well into development. Research on sexual size dimorphism in lizards shows that the divergence in growth between males and females can begin around 180 days of age, with clear differences visible closer to 250 days. Before that window, juveniles of both sexes look nearly identical in body proportions.
Behavioral Differences
Male lizards tend to be more territorial and display-oriented than females. Head bobbing is one of the most recognizable male behaviors: rapid, rhythmic up-and-down movements of the head used during courtship and territorial signaling. Males also perform “shudder displays,” which are bursts of short, rapid head bobs directed at females or rival males. These displays require significant energy and are far more common in males.
Females are generally less active in their signaling. Some female lizards perform a slow arm wave, raising one front leg and rotating it in a circle, which is thought to signal submission or acknowledgment to a displaying male. While behavior alone isn’t enough to confirm sex (some females head-bob and some males are passive), consistent territorial displaying or courtship behavior is a strong supporting indicator.
When Sexing Becomes Reliable
Very young lizards are difficult to sex visually because their reproductive anatomy hasn’t developed enough to see. For leopard geckos, the typical threshold is 5 to 6 inches in total length. For many other species, the first few months of life are essentially a guessing game unless the species has a feature visible from birth, like the tarsal spurs on veiled chameleons.
If you need to sex a juvenile lizard and visual methods aren’t working, a veterinarian experienced with reptiles can perform a procedure called probing. A small, lubricated metal probe is gently inserted alongside the vent and directed toward the tail. In males, the probe slides into the hemipenal pouch and advances a relatively long distance (roughly a quarter of the tail length, depending on species). In females, the probe stops after only a few scales because there is no pouch to enter. This method is accurate but carries a risk of tissue damage if done incorrectly, so it’s not a DIY technique.
How to Handle Your Lizard Safely for Checking
Never grab a lizard by the tail. Many species can drop their tails as a defense mechanism, and while the tail typically regrows, the replacement is never quite the same. Instead, support the lizard’s body from underneath with one hand while gently restraining it with the other. For nervous or flighty lizards, draping a small towel over their head can calm them significantly by blocking their vision.
When flipping the lizard to inspect its underside, move slowly and keep a secure but gentle grip on the torso. If the lizard is thrashing or clearly stressed, set it down and try again later. Stressed lizards are more likely to bite, drop their tail, or injure themselves. For larger species like iguanas or monitors, wrapping the body in a towel while leaving the vent area exposed gives you a safe window to check without risking a scratch or tail whip.