Breeding Aggression in Male Iguanas

archived 10-22-99
Archive file# r102299d
donated by James Vandale

Breeding Aggression in Male Iguanas

This document deals primarily with breeding aggression in male iguanas, but many of the techniques are suitable for use with just plain old aggressive (dominant to humans) igs.

Breeding Season Aggression

There is a way to deal with male breeding season aggression which does not include euthanasia, neutering or giving it away. It does include humans taking control, however! I have a friend who adopted a big 8-9 year old ig from the pound. She is tiny, and has two young kids, and freaked when he started charging. Once I talked to her about standing her ground and counterattacking, she and her kids have had no problems.

There are often triggers - the wearing of certain colors and time of the month (menses and/or ovulation) which can trigger attacks, so start paying attention to what is going on at the time of an attack. I know that when I wear blue, purple or green I incite one of my males -- he'll come flying across the room at me, or try to grab me when I walk by, so I watch him carefully during these times. I also pre-empt his strike with one of my own, picking him up and carrying him around for a bit, or getting into an extended petting session. I AM careful to keep watch, however, 'cuss the little brat knows when I'm distracted!

Tone Of Voice

They may not understand your words, but they know when you are ticked. Speak loudly and firmly - I find "Bad iguana! Baaaaaad lizard! Don't you even think of doing that!" to work quite nicely - the words don't really matter, but the tone of voice does. Shake a pointed finger at him while you are doing this. Stance Adopt an aggressive stance yourself: Feet planted apart, hands on hips, arms akimbo, bent forward at the waist slightly towards him. This will make you look bigger to him.


If he's still not getting the message, charge first, or charge back. Stomp your feet, make big movements. Remember, you are showing him that that you really are bigger than he is (rather than just being a big wimp! ;) and not afraid of him.


He will still have pent-up energies, and you don't want a neurotic ig on your hands... I find a green dish towel works very well. Dangle one for him, and let him grab it, roll in it, whatever. My paramour used to stalk me, and then, knowing there was no way I was going to let him get me, would sneak up on my couch and the green throw I kept on it, grabbing it, rolling up completely in it, laying still for a bit, then unrolling and doing it all over again. Three or four times of doing this, and he was ready for a cigarette and a nap. I will also come home sometimes and find my dishtowel all twisted up (and slightly damp) in the middle of the kitchen floor or dragged into the den. If you do get bit, don't jerk your hand away (if you can!), and absolutely do not put him down! If you do you will have reinforced that behavior. Just get someplace where the blood won't ruin anything, go through your "Baaaad lizard!" routine, and keep holding him for at least a minute or two before putting him down.

This tends to freak out friends who may be around when this happens, but you can deal with them (after you take care of the ig and yourself! Photoperiod In talking to many folks with suddenly super-aggressive breeding season igs, I have found one common factor between them - all have their supplemental lights on for more than 12 hours a day...some as long as 16 hours. We have been trying cutting down the supplemental lighting period to only 10 hours, from 8 am to 6 pm. This allows for a natural sunrise (about 6 am during the summer) and sunset (about 8:30 during the summer).

Another way that has worked to cut through a prolonged breeding season is to trick the iguana's system. Provide a comfortable basking area in a dark room - use heating pads and nocturnal lights or ceramic heating elements to provide the heat. Keep the room completely dark (close blinds and drapes, don't use any white light) for three days. When you take the iguana out after the three days, make sure you stick to a rigidly diurnal schedule for several weeks.

Diurnal Schedule

Some owners are, by choice or happenstance, nocturnal by nature. While this may be fine for humans, it is not for a diurnal animal. Iguanas need to sleep at night. They need to eat during the day. They need a length dark period at night when they sleep. If you work at night or get up late in the day and stay up till the wee hours of the morning, that's fine - just don't force your ig to the same schedule. It will affect his or her overall growth, health and, with males, can lead to more and prolonged periods of breeding aggression.

A Note on "Suddenly" Aggressive or Strange Behavior...

"My iguana is six years old and has always been real sweet and friendly. All of a sudden he is going nuts! He's gotten very aggressive, chases me, and oh, yeah, I must be feeding him too much squash because he's turning orange!" "My female is suddenly acting weird! She's five years old, and has always been pretty inactive. Suddenly, she is pacing her tank, digging at the floor and substrate.

What should I do? What's wrong with her?!"

It isn't strange and sudden - it's quite predictable, occuring same time every year, once they hit sexual maturity. They should reach sexual maturity at 1.5 years of age if they have been fed and housed properly, anywhere from age 3-6 if not.

The sad thing is that the only reason so many owners think that these behaviors are "strange" and "sudden" is that, to date, most igs have died before attaining sexual maturity. Now that we are getting better diet information out there and better veterinary care, igs are finally living a bit longer and attaining maturity, albeit late in still too many cases...

Iguanas need space to roam - males to 'protect' their territory, females to find nesting place. Most enclosures sold or built for igs are way too small. This results in increased aggression from increasingly frustrated males (often compounded by more than 10-12 hours/day exposure to UV A or UVA/UVB, with this supplemental lighting being kept on until late at night), and may cause injury as they bash their face against the enclosure wall, rip their toes trying to claw out, and trash their tail whipping it in such confined quarters.

I find that giving most males as much time as they want in front of a mirror each day, and freedom to roam around, dragging their thighs to their heart's content, results in an uninjured, well-balanced healthy male.

Yes, I still have to watch my colors with a couple of them, and it is rather cute to see them 'act like gentlemen' and stand up when I enter the room (actually, presenting to me, collapsing like puppies when I stop to pet them, as long as I keep my hand carefully away from their open mouth!). But I am always aware of what is going on, and who is in an aggressive breeding mode, and mitigate my behavior accordingly if neccessary, depending on the individual.

Some vets recommend castration/neutering as a way to end the aggression...the only problem is that this doesn't work very well - often not at all. Noted reptile veterinarian Douglas Mader recently went back and talked to ig owners about their neutered igs and found that results were less than gratifying. Dealing with them behaviorally, reducing photoperiods, being very conscious of their environmental set up and your own behaviors, and carefully and thoughtfully observing your males will help make breeding season less stressful for all of you.

A note on breeding season females...

Females in the wild often travel miles to their preferred nesting spot, and then may spend days digging and defending their sites from other females. Restricting them from doing so not only results in the injuries described above for males, but increases the risk of egg retention; coupled with the fact that the too-small enclosures do not allow for proper exercise, it is no wonder that egg retention/binding is the number one problem with sexually mature females. To find out more about egg-binding (dystocia), please check out my article on this subject. Gravid females often become more receptive to handling and petting. This can help increase the level of taming and socialization if your female has been more distant or less receptive to interactions prior to the onset of her first breeding season with you.

Kaplan, Melissa. 1996. Dealing with Iguana Breeding Aggression.
1996 Melissa Kaplan; updated 12/96

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