Aggression in captive reptiles comes in two main forms: aggressive behavior between cage-mates (intra-species aggression) or aggressive behavior between the reptile and the owner (inter-species aggression).

Reptiles at the greatest risk for aggression-related disease and injury come from households with:

• a single large male iguana
• animals kept in high densities in the enclosure (especially juveniles)
• reproductive animals kept in the same enclosure
• multiple males in the same enclosure
• competition for limited resources (hide areas, basking sites, feed stations) between cage mates.

While reasons for inter-species and inter-species aggression are varied, some of the more common causes are centered on improper husbandry practices, reproductive behaviors, and defensive behaviors.

It is common to see cage-mate trauma in small enclosures with multiple animals in them (high density). Missing toes, missing tail tips and bite wounds are often seen, especially in juvenile animals who think moving toes and tail tips are food.

Males of most species cannot be kept together as adults. Many species are highly territorial, including chameleons, iguanas, and some turtle and tortoise species. When kept together, these species will be in constant combat or one of the animals will be kept from a limited resource such as a basking area or hide area. These combats or the inability to access resources leads to stress and immune suppression. Lack of access to resources can lead to diseases commonly seen in captive reptiles including reduced feeding, failure to thrive (just not doing well), bacterial and fungal disease, reduced breeding, and skin problems.

Reproductive behaviors in male reptiles are often termed offensive aggression and frequently lead to dominance behavior. The iguana sees the male owner in the house as a threat to territory or for mates (female in the house) and this can lead to attacks on the male owner.

Defensive behaviors or aggression are associated with a threat, or a perceived threat, such as a cage-mate or a human displacing the animal from a basking site, perch or food bowl. One of the most common causes is when the owner attempts to handle the animal. In the wild, attacks from predators come from above so when owners attempt to handle their pet by grabbing them from above, it can be perceived as an attack and the animal may defend itself by biting or tail whipping. The reptile considers its cage as its territory and many species, especially large male iguanas, will defend this territory when an owner invades by reaching into the cage for handling or cleaning.

Affected Species

Any species of reptile can be affected by cage-mate aggression or can demonstrate aggressive behavior towards cage-mates or owners. Large, territorial species such as green iguanas (Iguana iguana), spiny-tailed iguanas (Ctenosaura sp.) and rock iguanas (Cyclura sp.) are more likely to show aggressive behavior toward owners although any species can be affected by cage-mate aggression and the stress associated with it.

Diagnosis

Your veterinarian will start by taking a thorough medical history, ask some detailed questions about your husbandry (especially cage set up, how many animals in each cage, basking site numbers) and give a physical examination. Answers to these questions will often be enough to give a diagnosis of aggression. A good thorough history and physical examination will diagnose the vast majority of aggressive behavior problems.

Tell your veterinarian what happens when you see aggressive behavior: fighting; chasing; mounting; biting by cage-mates; different activity levels by cage-mates (one very active the other less active); one cage-mate dominating the food bowl, basking branch or hide area; one cage-mate always in the dark, cool corner of the cage; or same age cage-mates but one is much larger than the other. Even if you don’t see any of these examples in your animals, remember that anytime there are multiple animals in a cage, there is the possibility of aggressive/dominance interactions.

When talking about the larger species of iguanas mentioned above, such as green iguanas and rock iguanas, there will usually be a seasonal (usually late fall or early winter, but can be anytime) rise in aggressive behavior often directed at the male human. The characteristic behaviors seen involve territorial threat displays that include head-bobbing (rapid or slow head movement up and down), tail-whipping, biting, and stiff gait with a puffed-up body turned to the side.

Aggressive attempts to mate with the human females in the household are not uncommon, and include bites to the face and neck because that’s where male iguanas grab female iguanas for breeding. These mating attacks are often associated with red clothing or time of menses. Generally, you will see increases in femoral pore (large waxy plugs on the undersides of both thighs) secretions that occur during the breeding season from increased amounts of testosterone…. BOYS!

Treatment

You and your veterinarian should discuss ways to reduce or eliminate any conditions that may be leading to aggressive behaviors.

Cage-Mate Aggression

Increase the size of the enclosure and reduce the number of animals in each enclosure. Keeping most reptiles individually, except during breeding attempts, is often the best density. Keep only like-size juveniles together. Make sure that there are enough basking sites, hide areas and feed stations for each animal in the enclosure, and monitor these to see if one animal is keeping the others from a particular resource. There is no specific answer to how many juveniles can share the same space; you have to monitor for aggressive signs and be prepared to move some. Note that most reptiles are born in litters.

Don’t keep adult males together in the same enclosure (especially those that are territorial, such as iguanas). If aggressive problems and interactions are seen, separate the aggressive individuals from the rest.

Free-roaming in the house is a no-no as the adult males will consider the whole house as their territory.

Reproductive Aggression (Human-Reptile Interactions)

Keep a record of aggressive interactions to see if these are associated with anything such as clothing color or menses/ovulation. You can then modify clothing choices or steer clear of the animal during those times. This will also help to determine any patterns to the attacks (e.g., attacks when a man is there, or when two particular animals are near each other), and work to modify or avoid those situations.

Changing the room or the enclosure that the aggressive animal is in will often reduce territorial aggression for a time. Moving the aggressive animal to another room by itself doesn’t change long-term behavior as the new area will eventually be looked at by the reptile as its territory. Providing a surrogate, such as a stuffed toy or towel for mating behaviors of breeding males, has worked well in some cases.

Your veterinarian may discuss neutering to help with reduce aggression in some species. This has helped in some cases but only when done before breeding season begins, and usually only in young iguanas before they reach sexual maturity.

Defensive Aggression

Always use calm, gentle movements around aggressive individuals and reach for them from below by sliding a hand under the animal’s belly. This will reduce the flight and fight response of defending themselves from a perceived attack by a predator.

Prognosis

Reproductive and defensive aggression behaviors can be difficult to change and can be frustrating to deal with, while enclosure problems leading to cage-mate aggression can usually be cured once they are recognized.

It is important that you and your veterinarian work closely together to solve these problems as no single treatment will work for all situations. Oftentimes each case needs multiple treatments and modifications.