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Aggressive Iguana

Why has my iguana become so aggressive and territorial?

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I would like some advice regarding my 4-foot male green iguana please. He has recently become very aggressive toward me and after some research, I realize that this may be because he has reached adulthood. I have been advised that castration would be an option, but would this definitely solve the problem? I have had him for approximately four years, and he is usually placid and enjoys human contact (although he’s now too large for me to handle!).

There are a lot of opinions on aggressive mature male iguanas, and no easy answers!


Iguanas are very territorial, and become very protective of their immediate environment. They are also solitary creatures, only coming together to reproduce. I assume you are housing him alone?

A few years back, REPTILES magazine published an article and very graphic photographs that were submitted by the owners of a large male iguana that had recently become very aggressive, especially to the female of the couple. While the iguana had lunged at her a few times, she ignored the signs and entered his walk-in cage one day, anyway. He attacked her face, biting her ferociously, and she ended up needing several plastic surgical procedures to correct the injuries, although she was left with some scarring.

While neutering (aka castration, or the removal of the testicles) is suggested by some as a way to lessen aggression, this is not always reliable. Using hormones to try to lessen the aggression of a mature male is also not predictably successful, either. I wouldn’t rely on either method as a sure-fire way to return your male green iguana to safe-pet status.

That said, from now on, you must be very careful when dealing with this male. Some males become more aggressive during breeding season (springtime), and they are more docile at other times of the year. You will need to learn his signs for when he is acting territorial and aggressive, and avoid injury. ALWAYS be on your guard when you are around him and don’t allow friends or relatives near him ever, even if he seems to be acting okay, as they can suddenly lash out.

I’m sorry that there is no surgical or medical treatment that will effectively “defuse” your iguana. I hesitate to recommend something, as the failure rate is too high to make any technique reliable. Good luck with him and stay safe!