Many of the issues and signs of problems addressed in this article are applicable to other iguanid and agamid species with similar social structures, including anoles, water dragons, bearded dragons, even in leopard geckos.

Many iguana keepers, by intent or by chance, find themselves considering taking in a second iguana - or suddenly find themselves with another iguana. The most common question, then, is "can I house them together?" The answer is, "It depends..."

It depends on the individual iguanas and their temperament, stage of development, and/or time of year. It also depends on the housing situation. Given that most iguanas are kept in enclosures that are too small for them, introducing a second iguana into the enclosure is certain to create major problems for one or both of them. Size and sex doesn't necessarily matter, as females can be territorial and small iguanas can be incredibly nasty to more docile larger ones.

Here are some questions I've been asked and my responses to them, as well as recommendations for introduction and housing.

Housing Multiple Iguanas

"I hear you can't keep more than one ig together. Is that true?"

"I saw a video that said igs can smell each other and one will stop growing if another ig is brought in. Is that right?"

"I've heard that you can't keep two males together because they'll kill each other."

Well, yes and no.

If you have an iguana and are thinking about getting another iguana, you can, just so long as you are prepared to set up separate housing if need be. Big igs often get along just great with little ones, and females can be just as territorial as can males. In other words, there are no hard and fast rules other than for you to be prepared to create separate environments for them, permanently or seasonally (during breeding season) if need be.

In the wild, iguanas have a very dynamic social hierarchy. Males stake out territories and there is always a dominant male in any group. In a large population there may be several dominant males but they may keep some distance between themselves. Subordinate males will challenge dominant males, sometimes succeeding, sometimes not, retreating to the outskirts of the colony group to try again another day, another year.

One of the biggest problems with getting a second iguana is that most people have enclosures that are too small for one iguana let alone more than one. The smaller the space you try to keep them in, the greater the risk of agonistic behavior and of one or both getting injured or sick.

Agonistic behaviors are those behaviors associated with dominance. They may be overtly aggressive, including such behaviors as chasing, attacking, butting, posturing, etc. Agonistic behaviors can be quite subtle; if you've ever been on the receiving end of one of your iguana's "looks," that out-of-the-back-of-their-eye glare, or sniff of disdain, then you have some idea of just how effective it can be! By mere posture, a subtle or minor shift in position, one iguana can keep another away from food, water and basking areas. This will result not only in a malnourished iguana, it also results in a great deal of stress. Prolonged stress affects the functioning of the immune system, suppressing it, resulting in greater susceptibility to infection, increase in colonies of otherwise commensal worms and protozoans, ultimately leading to failure to thrive, even death.

Igs don't even have to be housed together for this to happen - just being able to see another iguana who demonstrates agonistic behavior may be enough to affect a subordinate ig.

The size of the iguana alone does not determine who will be dominant and subordinate. I've seen big igs who are wimps and small tough guys. I've had males come in and immediately signal submission who later got healthy enough and well-balanced enough to start challenging the alpha and beta males. I've had females come in and displace the alpha female and even challenge the alpha male. I've had igs who were too chicken to challenge any of the other igs but who will, at the drop of a hat, challenge humans, the tortoises, the geckos, or their mirrored reflections. Some just carefully look around to make sure they are alone...then bob and posture to their heart's content, seemingly encouraged by the fact that no one's around to challenge back.

Introducing Iguanas When keeping more than one iguana together, introduce the new iguana to the established one in a neutral territory. Do not put the new iguana directly into the established iguana's enclosure. This is construed as a direct threat to the established iguana's territory and that iguana, especially if both are males, will go on the attack.Have both iguanas out into a neutral area. Hold, pet, and talk to both of them. After a half hour or so, put the new iguana into the enclosure and give it an hour or so to familiarize itself with the new environment. If there are different levels within the enclosure, physically put the iguana on the different shelves and show it the way to get up and down. Show it the food and water bowls.Once the new iguana has been settled in for a while, then reintroduce the established iguana into the tank. Watch them closely for the next several hours.

Keep a close watch on them for the next several weeks. You need to make sure that both of the iguanas are feeding and have free access to the basking and hiding areas. There is the possibility that one of two iguanas will prevent, through intimidation if not through active physical force, the other from getting enough heat, food, water or physical space.

Clues that this is happening include one iguana visibly losing weight (watch the hips and base of tail), turning dark (sign of stress), and acting lethargic. If any swellings or bumps occur, they may be signs of infection or abscesses from bites or scratches that may have gone unnoticed by you, or which are caused by bacteria that has proliferated unchecked by the stressed iguana's depressed immune system - another symptom of stress.Be prepared to set up a second or third feeding station and alternative basking areas in your ig enclosure or room...or house. If your enclosure isn't big enough to do that, then that tells you that you need to get a bigger one (which is great because then you move them both into neutral ground), or set up a second enclosure/basking area. Set up basking and sleeping areas at different heights. Provide some visual screening so that igs may get out of line-of-sight from other igs if it so wants.

Spend a lot of quality time with the original ig - if you've ever introduced a human baby into a house with a long-term cat or dog resident, or a new sibling to an older child, feelings of displacement can affect overall behavior...and it is no different with igs. Try not to always flaunt the time you spend with the new one in the face of the original one for the same reasons.

Stressed iguanas, both the aggressor and victim, may also suffer from an upsurge in parasitic infestations, including endoparasites such as worms and protozoans, and ectoparasites, such as mites, especially if the new iguana came from a stressed (and less than clean) environment. All new iguanas should routinely have fecal exams done; all iguanas who show signs of stress for any length of time in excess of a couple of weeks or so should also be tested.

Important Note

Do not introduce a new male iguana into the household during breeding season. Even if they cannot see each other, chances are great that the established iguana will know that the new one is there. Remember that their sense of smell is more acute than ours, and they pick up cues to which we are blind or otherwise senseless.

Interspecies Conflicts

The types of problems discussed above can also happen between lizards of different species, or in one lizard and some other species, including other types of lizards, dogs, cats, birds, even humans. This may occur even when the target species has done nothing to invite such a response.