Strutting their Stuff: Mexican Black Spiny Tailed Iguana Rut
Tara A. Spears
One of the standout animals that one notices when visiting coastal Mexico is the ubiquitous lizard. Besides the diminutive geckos there is the larger, more exotic iguana. The two types of iguanas that are in the Riviera Nayarit are the Green Iguana and the Mexican Black Spinytail, although there are hundreds of species worldwide. Watching iguanas is always relaxing but it’s especially enjoyable during the month of April when iguanas are in rut.
These reptiles are common in the lower altitudes of tropical Mexico. Feeding time will usually be late morning, after the iguanas wake up with the sun and find a nice basking spot to warm up. After feeding, iguanas typically will return to basking to obtain the heat necessary to digest their food. Iguanas are excellent swimmers, so don’t be surprised to find them in your pool. Since they are ectotherms, they require the energy from the sunlight for their bodies to function, thus requiring them to sleep through the night and stay awake during the day. Their poop is generous and they leave it everywhere: pool decks, walls, patios and rooftops.
The male Mexican Spinytail is mostly black with white and yellowish blotches; females can have an additional greenish tint. Their most distinctive feature is the dragon-like spiny fringe that runs down the center of their upper back and tail, hence the name. Coming into rut causes an orange coloration in the males. Mexican Spinytail babies are bright green with black markings. Mexican Spinytails can grow up to four feet (1.3 m) in length and weigh about 15 pounds (7 kilos). Wary and alert, the Mexican Spinytail is not a common sight in the wild, but they are attracted to cultivated flowers so it is typical to see iguana in warm residential areas. Because the Black Spinytail has an attitude, it can be problematic for domestic pets.
According to lizard expert Virginia Aronson, iguanas in the wild attain sexual maturity at about 18 months of age. Males will develop orange or rusty red coloration on his head and neck, back, and the tops of the legs, besides their behavior will become aggressive. You will see posturing, including increased head bobbing, restlessness, lateral compression of the torso (“hatchet mode” or “hatcheting”), dewlap flaring, crab-walking, and ritualized tail movements.
Wild spinytail males are in season for about 30 days. During that time, they exhibit the color and other changes. Since females roam throughout the territories of several males, and are themselves receptive to mating for only 7-10 days, males mate with several females during the month they are in breeding mode. A female who isn’t receptive is left alone after a generally simple rebuff (head bobbing, foot swatting, or tail lashing). Since males mate with potentially 15-18 females in the wild (they generally mate on one day, rest the next, mate the third day, rest the fourth, etc.).
Keep in mind, too, that females don’t have to be mated, or even within a mile, of a male to become gravid (carrying eggs), so not only would you still have a male on the make, you could conceivably (no pun intended) have 15+ gravid females, who can have potentially 30-60 offspring. So that means each horny male can produce 450 additional iguanas a season! Iguanas in rut go potty more than their usual once or twice a day- males do it as a sort of territorial marker, females because as the eggs start taking up more room in their abdomen, their internal organs get compressed and they are unable to store wastes as long as they used to. This explains why there has been more mess in my yard.
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Iguana body language: Since we have to coexist with these reptiles, it’s good to learn Iguana language. They don’t make a lot of noises so you have to pay close attention to body language. What looks like a “smile” is actually a snarl. It’s a warning for you to back off. I used to enjoy watching the iguana antics, after years of aggression towards my dog or me, I have learned to be aware of the iguana’s attitude when I’m working in the garden or relaxing in the pool. Both sexes do head bobbing. It is typically used in an aggressive way or to assert dominance, and head bobbing is generally executed by iguanas that are secure in their surroundings.
An iguana’s teeth, which are recessed and attached to the inner edge of the jaw bone, may not be clearly visible at first glance, but they’re there. In fact, a full grown iguana has 120 razor sharp serrated edge teeth capable of inflicting serious injuries. Their teeth are instrumental to their survival since they assist them to efficiently slice through leaves and other plant matter essential to their diet. 
One type of iguana bite is the “slash and tear”. This is an aggressive one. It means to show you who is the boss. It can come without warning but might be preceded by a snarl (a slightly opened mouth) or puffing and walking sideways while glaring at you. Watch the eyes. If they are wide open, look out! If the tail is starting to twitch, back off immediately. My small dog has been the victim of this type of iguana bite with serious consequences. Mexican black spinytail iguanas are toxic to dogs: the iguana carries Gram negative bacteria(Salmonella) that will cause the dog to vomit if the dog even mouths the lizard. If the dog is bitten by the lizard, the lizard’s mouth transmits the bacteria causing an internal infection to the canine. Wash the dog’s wound immediately and go to the veterinarian as soon as possible if your dog tangles with a black iguana!
All black iguanas (garobo in Spanish) are territorial and will defend the area they live in–including your entire yard. Since Mexican Black Spinytail iguanas are prolific in Jaltemba Bay, you cannot eliminate them but you can try to make your yard less inviting.
