Blue Iguana Recovery Program

Blues and Greens

Blue Iguanas & Common Green Iguanas, the differences

realblueCommon Iguanas (Iguana iguana), also known as Green Iguanas, have escaped from the domestic pet trade on Grand Cayman, and are breeding in the wild throughout the western districts of the island. They are native to Central and South America, where they evolved in the presence of many predators. Common Iguanas therefore have instinctive strategies to avoid being eaten by cats and dogs, and they are thriving in suburban areas where Blue Iguanas would not stand a chance.

Common Iguanas are now numerous and sighted often, while the critically endangered Blues are almost never seen outside protected areas. More and more, people are beginning to mistakenly assume the Common Iguana actually IS the Cayman’s own Blue Iguana!

Click to enlarge

Click to enlarge

The two species are very different, and can not breed together. They don’t even speak the same “language” – when a Blue Iguana threatens a Common Iguana by head-bobbing, the Common Iguana does not understand. Size for size, the Blue Iguana is much stronger and much more aggressive.

To tell them apart, look at these pictures, and note these characteristics:

  • Common Iguana has spines on the dewlap (the skin flap under the chin), The Blues never have spines here.
  • Common Iguanas have a very long, whip-like tail, with vivid black bands. Blues have a thicker tail, without obvious bands.
  • Common Iguanas have a large circular scale, like a shield, on the cheek beneath the ear. Blues have their cheeks covered with cone-shaped, pointed scales when they are old, and never have a large circular one.

Blue Iguana’s Relatives

The Blue Iguana is one of the West Indian Rock Iguanas, which are all classified in the genus Cyclura. Uniquely different species of Cyclura are found from the Virgin Islands through the Greater Antilles to the Bahamas.

The most ancient Rock Iguana is Cyclura pinguis, which survives on Anegada. Like the Blue Iguana, it is now critically endangered. It was the ancestor to this iguana which dispersed first from the Puerto Rico bank to Hispaniola, then onwards to the north and western islands, which has since diversified on different islands into 9 species and several additional subspecies.

The Blue Iguana evolved more recently from ancestors of its nearest relative, the Cuban Iguana (Cyclura nubila). Cuban Iguana ancestors also made the crossing to Little Cayman and Cayman Brac, where they evolved into a unique subspecies, Cyclura nubila caymanensis, and to the southern Bahamas where they evolved into a new species, Cyclura cychlura.

The Blue Iguana was long thought to be another subspecies of the Cuban Iguana, and but recent genetic evidence has led to a revision, and the Blue Iguana is now considered a unique species, Cyclura lewisi. If Cyclura lewisi and Cyclura nubila caymanensis are artificially brought into contact, they can still breed and produce fertile offspring. Naturally, they have always been separated by at least 67 miles of open ocean.