Beware the Spiny Tail Iguana in Rut

Tara A. Spears

‘Oh, Spiny Tail Iguana, how I hate you,
Let me count the ways…’

Originally, I thought the flashy iguana exotic and interesting to watch. But after 25 years of territorial dispute, and three unprovoked attacks on my pets, I hate them. Originally, I had laughed at friends and neighbors when they complained about the iguanas pooping on their patio and eating their flowers. I laugh no more, because I’m tired of cleaning up the iguana poop, tired of the females digging nests in my flower beds, and mostly I am furious that these reptiles attack my innocent dog. I wish them well, but I wish the Mexican Black Spiny Tail iguanas would choose someone else’s yard.

March-April is the rut season in Jaltemba Bay, and as with many species, the males get aggressive. They exhibit a variety of coloration patterns, but the male Mexican Spiny Tail 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 Spiny Tail babies are bright green with black markings. Mexican Spiny Tails can grow up to seven feet (2 m) in length, and weigh about 40 pounds (18 kilos). Wary and alert, these territorial creatures tend to be defensive in the wild.

According to herpetoculturist Melissa Kaplan, Mexican Spiny Tail males are in season for about 30 days. During that time, they exhibit sharpened coloring and more posturing — head bobbing and hissing. Since females roam throughout the territories of several males, and are themselves receptive to mating for only 7-10 days, the males mate with several females during the month they are in breeding mode.

The reason iguanas are so prevalent in the Mexican tropics is that there aren’t many predators to control the population, and the Spiny Tail iguanas are prolific breeders. Each male can potentially mate with 15-18 females each rut season in the wild (they generally mate on one day, rest the next, mate the third day, rest the fourth, and so on). 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 have 15+ gravid females, who can each have 30-60 offspring. That means each male can produce as many as 450 additional iguanas in a season. Wow.

As to the harm to dogs, the black Mexican Spiny Tail iguana has bacteria on its skin that is toxic. So when your fur baby bites an iguana, it is necessary to administer an antibiotic besides treating the wounds. In one encounter, a male in rut attacked my little dog. The iguana was not cornered — it came voluntarily into the yard, and all my dog did was stare at it before the lizard leaped to bite her. I had to hit the iguana with a broom to get it to release its grip; my little girl never got a bite in to protect herself. The dog ended up with three wounds from the accidental encounter.

While an iguana appears to be toothless — their teeth aren’t visible above the jaw like carnivores — this plant eater has a powerful bite, with 120 recessed, razor-sharp teeth. In fact, a full-grown iguana has serrated-edge teeth capable of inflicting serious injuries. Their teeth are instrumental to their survival, since they help them efficiently slice through leaves and other plant matter essential to their diet. A hungry iguana can level a shrub in one meal.

Keep an eye on the iguana’s posturing. What seems like a smile is actually a warning that it’s about to attack, along with puffing up and walking sideways while glaring at you. Watch the eyes — if they are wide open, look out. If the tail starts to twitch, back off immediately. If your pet is bitten, or even if it grabs an iguana, go immediately to the vet.

The prehistoric-looking Mexican Spiny Tail iguana is best seen from a distance in the spring. It’s quiet — but oh, can it bite!