Aggressive Behavior: As a rule most iguanas that are obtained as young juveniles and are handled correctly do not tend to become aggressive, however there are a few exceptions to this rule. One of the biggest is the tendency for adult alpha male iguanas becoming aggressive in a home where the primary human handler is a female. The reason for this aggression has been linked to a pheromone that is produced by the human female during her menstrual cycle. This pheromone is very similar to that produced by an adult female iguana during the mating season. This behavior may be curbed by providing a surrogate mate during this period such as a stuffed animal or a rubber glove.
Aggression by one iguana towards another is usually witnessed in alpha male iguanas who are very intolerable of another alpha male or even a beta male which will not mate with females. Beta males are usually very tolerant of alpha males, females and other beta males and therefore make the best captives.
Aggression in females is seldom seen because females are tolerant of other females as a result of the fact that one alpha male will mate with a small group of females. Iguanas who become aggressive may often times be "tamed down" through gentle handling in a non-aggressive or threatening manner such as approaching the iguana from the front allowing it to see you approaching it and holding it by its belly allowing it to rest on your hands and arm like a branch rather that grabbing it by its back like a predator. Iguanas have a type of third eye located on the top of their head, which sees shadows.
This "third eye" also serves other functions and plays a role in thyroid production, but it also allows the iguana to detect predators such as birds as they approach from above and when you reach in and grab your iguana from above by its back you become the bird and cause the iguana to become aggressive by eliciting a fight or flight response.
Cage Mates: It is recommended that iguanas all be housed separately to avoid aggression by males toward females while trying to breed and toward lesser males as well as to avoid the spread of disease by the transmission of bacteria through wounds caused by the nails of iguanas who will climb on top of each other when housed together within the same enclosure.