The spiny-tailed iguana is a large iguanid but it is not the same as the green iguana that many people are most familiar with. In Costa Rica, both green iguana and spiny-tailed iguana are common, but the spiny-tailed is certainly more abundant - and much more conspicuous - on the Pacific coast.
The spiny-tailed iguana is a large and robust lizard, with big males reaching over three feet in length and attaining a massive girth. They are heat loving lizards and even on the hottest days may be seen basking on inclined trees, rock piles and on fence posts bordering pastures. This species is called spiny-tailed because the tail is ringed with short spines which the lizard will use as a weapon when threatened and not given an avenue of escape. Even though spiny-tails can climb quite effectively, large individuals seem to have a preference for staying closer to the ground. In some areas, such as Manuel Antonio National Park, these lizards walk along the trails, on the beaches and they seem to enjoy basking on the slightly curved trunks of palm trees just above the high tide line. It is not unusual to see spiny-tails and white-faced capuchin monkeys on the same palm tree or even on the same picnic table as well.
Young spiny-tails eat a wide variety of invertebrates as well as smaller lizards. While staying at one of the lodges during a Costa Rica tour , I witnessed a young spiny-tailed iguana catch an ameiva lizard and gobble it down. As the lizards reach maturity, their diet becomes much more vegetarian and leaves, flowers and fruits make up much of the diet of these very large lizards. Occasionally unusually large male iguanas are observed, and in Santa Rosa and I once observed a male that was conservatively four feet in length. He was a breathtaking animal and I watched this monster for about an hour before heading to greener pastures.
Naturalist Greg Greer  is a favorite among IE travelers, and has gained a reputation for his friendliness and good humor, along with his incomparable knowledge of natural history, photos and articles have been widely published in books and magazines, including Georgia Outdoor News, Bird Watcher’s Digest, Alabama Outdoor News, Riversedge and Southern Wildlife.