As iguanas grow in popularity, due mainly to their personality (Iguanality), unusual looks, and low maintenance and spatial requirements, the chances of physical aggression between iguanas and owners becomes more likely. Iguanas are usually shy, passive, solitary creatures, but under the right conditions, they can aggressively defend themselves. Physical aggression in iguanas usually manifests itself in the form of biting or tail wiping (neither of these should be taken lightly as the whip-like tail of an Iguana could seriously injure an eye and their jaws are strong enough to sever a mouse's head from it's body in a single bite). There appears to be two basic reasons for why iguanas can become physically aggressive towards their owners; defensive response to a stressful situation and sexual aggression. Both of these situations can easily be avoided.
It is very important to understand that most Iguanas are wild caught and as such, are wild animals. If a wild animal is presented with a situation that it finds discomforting or threatening, it will usually act in one of two ways, fight or flight. Iguanas are herbivores, and as such, their natural mechanism for dealing with confrontational situation, especially one in which they could be the meal, is to flee. If an iguana is presented with a situation from it's owner that it finds uncomfortable or fearful, it will try to escape the situation. For instance, if you try to hold an iguana that does not wish to be handled, it will try to remove itself from the situation. Most iguanas in a captive environment are severely limited from fleeing a stressful situation. The cages they are usually housed in offer little sanctuary or places of retreat. If your iguana tries to flee a situation but cannot escape (for instance, holding them when they do not wish to be held), the iguana may react with it's only other means of protection, biting or tail whipping. This type of aggression is more of a defence mechanism to an unavoidable situation and as such, it is easily avoided with good observational skills.. Behaviour patterns of the Iguana that represent stress should signal to the owner that this a possibly a confrontational situation if it cannot remove itself from the situation. These include; startled response, skittish behaviour, avoidance of contact by running away (this is often seen by the animal clawing at the side of it's cage away from where your hand is coming from), repeated attempts of escape from your hands while being held, head bobbing (which is an overt sign of posturing), as well as other behaviours that may be specific to your iguana. The key here is to observe how your iguana reacts to you. If the animal appears stressed, or uncomfortable, cease the activity that you are doing. Aggression due to stress can be more prevalent in iguanas that are new to captivity, a new environment or new situations. You should always give your animal ample time to adjust to different situations, slowly introducing them to new situations. Physical aggression from your iguana can also be the result of inappropriate handling. Inappropriate handling, such as supporting the weight of your iguana by the tip of the tail, squeezing too hard around the rib cage, or rubbing too hard or too close to sensitive areas, may cause your iguana to bite in response to stress or discomfort. Iguanas, like most animals, should be held in such a way that promotes the safety of your animal as well as feel comfortable to your iguana. Iguanas should be held firmly around the shoulders (top side) and by the base of the tail (right behind the legs). For the most part, iguanas should not be handled any more than is necessary to promote good husbandry. This, of course, varies between individuals, but as a general rule, it is always safer to under handle your iguana than over handle it. Your iguana may wish to hold on to you by their own means, and without your help. This is usually less stressful for the animal, but if they do become scared, more than likely you will have a track of claw marks showing the path he took across your body.
There appears to be a strong correlation between overt, aggressive, physical attacks by iguanas and females who are primary care givers to these animals. This type of aggression has been coined "Sexual Aggression" and it appears to follow a specific pattern. Sexual aggression usually involves overt acts of aggression, such as chasing and biting of the owner. Mature, male iguanas who have been long term pets tend to be the main culprit. The owners are almost exclusively females between the age of 18 to 40 who are the head of the house hold and the primary care giver to the iguana. It also appears that the male iguana is in his mating season while the female owner is experiencing or within a few days of menstruating. It is postulated that the male iguana is sensing pheromones from the menstruating owner and reacts to these signals. This type of aggression appears suddenly and is quite violent in terms of normal iguana behaviour. There have been reported cases of iguanas chasing there owners across rooms and up stairs before inflicting a nasty bite to their legs. There are a few ways to avoid this type of overt aggression. The easiest solution is for the owner to place the iguana in an appropriate cage during the few sensitive days of menstruation. Another possible solution is to have the iguana's testicles removed surgically (castration) by your veterinarian. Both these options almost completely reduce the possibility of this type of aggression occurring. Another option to consider is the possible modification of the iguana's behaviour. However, due to the mental capacity of an iguana, behaviour modification techniques may not be the most appropriate option for an overly amorous iguana.
The key to avoiding physical aggression in your iguana is to have a basic understanding of iguanas in general, as well as keen understanding of the "iguanality" of your particular animal. Pay close attention to your iguana and remember to always approach and handle your iguana with care . Further reading that may help you in your understanding of your iguana can be found in a book called, Iguanas: A Guide To Their Biology and Captive Care, by Frye and Townsend. In addition, you may want to read the information provided by Patrick J. Morris, D.V.M. from the San Diego Zoo, Department of Veterinary Services on IGUANAS: BASIC CAPTIVE CARE CONSIDERATIONS.
Also, it is important to remember that reptile pets have been linked to cases of Salmonella. During 1994-95 health departments in 13 U.S. states have reported cases of persons infected with unusual serotypes of Salmonella in which patients had direct or indirect contact with reptiles such as lizards, snakes or turtles. For more information you may want to read the Reptile-Associated Salmonellosis Information Page.
Anderson, Nancy L. Husbandry and Clinical Evolution of Iguana iguana. Compendium on Continuing For The Practising Veterinarian.Volume 13, May-Aug: pg 1265-1269, 1991.
Boyer, Thomas H. Green Iguana Care. Association of Amphibian and Reptilian Veterinarians. Volume 1, Number 1: pg 8-11, 1991.
Frye, Fredric. Interspecific (Lizard:Human). Sexual Aggression in Captive Iguanas (Iguana iguana). Association of Amphibian and Reptilian Veterinarians. Volume 1, Number 1: pg 4-6, 1991.