Determination of sex in a sexually mature iguana is very simple. There are both primary and secondary sexual characteristics that indicate sex and unlike other reptiles, they are very reliable in iguanas.
Some of the secondary sexual characteristics of the male are a larger head and jaw structure, much like that of a tomcat, and the larger dorsal spines on the crest of the head. All iguanas have pours on the inside of their rear legs. These pours are much larger in males. The primary way to determine sex in the adult male iguana is to locate the hemipenes located just below the vent on the underside of the tail. There will be two very noticeable bulges on either side. These bulges are the hemipenes and are very hard to mistake for a normal part of the tail.
Determining sex in the female iguana is equally simple since her head and jowls will be much smaller and the dorsal crests greatly reduced. The pours on the underside of the rear legs will be much smaller and she will lack the characteristic tail bulges of the male. It is also important to note that the female is capable of producing eggs for several years after mating with a male iguana. She has the ability to store viable sperm for up to 4 years and may at anytime during that period produce fertile eggs.
It is very important to note that following oviposition by a female iguana; she will be very dehydrated, anorectic and even hypocalcimic as a result of the extra calcium required during egg development. A female should always be placed on a calcium supplement during and following the development and depositing of eggs. If she becomes too hypocalcimic her body will re-absorb the eggs inside her to replenish her body's needs and will still be capable of re-developing and depositing fertile eggs at a later date.
Since there are actually three sexes the Alpha male, the Beta male and the female it is important to note that only the Alpha male is capable of sexual reproduction. The Beta male looks very much like a female and is often mistaken for a female. The most accurate way to determine the sex of a Beta male is to look for the characteristic tail bulges from the hemipenes. Beta males will also lack the usual bright yellow and orange colors of the Alpha male and look very much like a female with reduced physical characteristics.
These methods for sex determination are not only reliable, despite popular belief, but are also a less invasive and stressful way to determine sex. Methods such an everting the hemipenes and probing are very invasive and since the presence of hemipenes in the adult male may be determined without the use of either of these methods it is an unnecessary procedure.
Alternative methods of sex determination include probing, hydrostatic evertion, manual evertion and radiographic sex determination. The primary draw back to these methods is the fact that they are either very invasive or cost prohibitive.
