Even then only a herpetologist can probably tell the difference. There are some behaviors as the iguana grows that serve as guidelines for sex determination. A head-bobbing motion in general is said to be a male behavior but in some instances has been observed in females as well. There are some basic facts that you should know about iguanas before you buy. The first thing is that iguanas need heat and light to survive.
Reptiles are cold-blooded animals and heat is essential to their well being.
The temperature should be between 78-85 degrees Fahrenheit. Heat is vital to the enzymes in the body, without these enzymes many chemical reactions in the reptile would not occur. If the reptile is too cold they may hibernate, stop digesting their food, or stop eating altogether. It is important not to make the environment too hot for the iguana either. Most reptiles regulate their exact body temperature by moving back and forth between the sun and the shade.