Don’t Step on the Iguanas!

A Story of Evolution in the Galapagos Islands

Iguana at Sunset

Sometimes, Galapagos tourists decide to ignore the rules and, like pirates of old, attempt to smuggle our rare and endangered species out of their natural habitats. One such example is the tourist who tried to take four iguanas through airport security in a suitcase. Bad idea! He’s now now serving four years in prison — one per iguana. As outrageous as this attempted theft was, it also serves as a reminder that our endemic iguanas are unique, amazing. and exotic. They would sell for lots of money to those who collect exotic species. Our job on Galapagos is to protect our remaining iguanas and to observe them in their natural habitats, keeping each species on each island safe and distinct.

People visualizing “iguana” may think “ugly” and even “repulsive” and “scary” — they wouldn’t want to face down one of these in a dark alley! But, an actually look at one of our Galapagos iguanas will probably change their minds. For our iguanas, living in Paradise, appear to have a perpetual smile on their faces, like this one from Sante Fe.

Land Iguana photo by Norine Audette 2007 from Galapagos Conservancy 500

Though land iguanas can be found in many places throughout the world, the ones in Galapagos are different. One species lives on Isabela, Santa Cruz, Fernandina, Seymour and South Plaza Islands, another on Sante Fe Island. And a third on Isabela. Except for those on Isabela, the land iguanas are often yellowish in color.

In 2009 the BBC News reported that the National Academy of Sciences was researching a unique species of pink iguana on Isabela at Wolf Volcano. It has a pinkish head, and pinkish and black body and legs, often with black stripes. When Wolf erupted in 2015, there was speculation that the pink iguana, already so limited in number, might become extinct. Fortunately, the pink iguana is safe. Still, there are fewer than 100 individuals remaining of this rare and endangered species of land iguana. They do not cross breed with the more familiar yellowish land iguanas and their crests and head shapes are different as well. The new species is morphologically, behaviorally, and genetically distinguished from the other two.

Iguana eating Prickly Pear Cactus

All Galapagos land iguanas do share characteristically tough, leathery mouths, enabling them to feed on the prickly pear cactus, their primary food source.

They also can digest poison apples, which are toxic to the human species. The Galapagos land iguana grows to a length of three to five feet with a body weight of up to twenty-five pounds; size and weight are different on different islands.

There are no more land iguanas on Santiago Island, mostly due to non-endemic predators, such as feral dogs and cats, as well as humans. This is a tragedy, particularly when you consider Charles Darwin’s report that when he tried to pitch a tent on Santiago, he had a hard time finding enough space because the iguanas were so prolific. They are also extinct on Baltra and southern Isabela.

Photos of Iguanas basking in the sun and cooling in the shade courtesy of Cindy Procter King and Aqua Surround
Hundreds of Marine Iguanas Warming Up in the final sun’s rays; photo by AquaSurround

All iguanas, both land and marine, are cold blooded. They just love basking in the equatorial sunshine or sometimes cooling down in the shade of a rock or burrow. Land and marine iguanas have similar mating and breeding habits as well. Land iguanas can live to be 60 years old.

Marine Iguanas

This marine iguana is larger than a curious sea lion pup

Galapagos marine iguanas — like so much in our island paradise — are unlike any other creature on our planet. Though many iguana species can swim, our marine iguanas are the only sea-going lizards anywhere in the world. Marine iguanas are found throughout Galapagos, and though the marine lizards from each island are distinguishable in color, size and features, they are all the same species. Their differences are, like so many things throughout the archipelago, natural evolutionary adaptations to their surroundings. The color differentiation provides the very best means of camouflage and protection.

Marine iguanas on every island are born black in color, and become more colorful as they get older. Actually, as is the case with many animals, the males develop colors to attract females, while the females tend to remain in shades of gray to black.

Here are a few examples:

Christmas Iguana on Espanola Island

This iguana is enjoying the sun on Espanola Island. It is identifiable by its reddish hue. The red comes from the specific type of red seaweed that it ingests and that blooms only on Espanola. These are generally believed to be the most colorful of the marine iguanas.

The iguanas from Santiago have different coloration. Often the Santiago iguanas appear to have a greenish tinge.

In addition to being distinguished by colors, male and female iguanas may be distinguished by their size. Generally, females are smaller than their male counterparts. It is the largest male iguanas that are the most sea-going.

Another amazing feature in marine iguanas is that when there is not much food around, which may occur during an el niño event when algae on which they feed cannot thrive in the warm water, they not only lose weight and become thinner, but also they get shorter in length as their backbone literally shrinks. Then, when there is enough nourishment and they start eating again, they regrow in both length and weight. Adult iguanas can switch between growth and shrinkage repeatedly throughout their lifetime.

The Galapagos iguanas eat a strictly vegetarian diet of seaweed and algae. Their food is as likely to come from the lichen growing on the rocky shore or a tidal pool as from the ocean itself. Marine iguanas have a blunt nose, which allows them to scrape algae off the rocks with their sharp teeth.

Very large marine iguana on Espinosa Point, Fernandina

Large male iguanas are very strong and can be as large as four feet long; half of this its tail. The large males have enough body strength to swim past the waves and dive underwater for food. Each dive usually lasts about 5–10 minutes, but the iguanas do have the capacity to be under water for as long as 45–60 minutes. They become more aerodynamic underwater and swim by moving their bodies and long flat tails from side to side, with their legs held to their sides. Also, marine iguanas have long, sharp claws which give them the ability to hold onto rocks along the shore without being pulled away by the waves.

Marine iguanas, like other reptiles, are cold blooded, meaning that they take on the temperature of their surroundings, unlike humans and other mammals with self-regulating constant body temperatures. Cold blooded creatures become hot in a hot environment and cold in a cold one. Thus, when swimming in the Pacific Ocean with its cold currents, the iguanas become cold. Their blood moves away from the surface to preserve heat and their heart rate slows.

This adaptation is very refined. The iguanas lie on top of each other to absorb and maintain the heat level. They lie perpendicular to the direction of the sun to maximize the amount of sun that falls on their skin. They are able to expand their rib cages to increase surface area for absorbing the sun and may even darken their skin, as dark absorbs whereas lighter tones reflect the heat. If an iguana gets overheated, it just slithers back into the ocean or under a bush or into a burrow and turns its body parallel to the sun.

The fact that dark absorbs and retains heat also explains why the iguanas are usually found basking on black volcanic rocks. During cooler times, the iguanas huddle in masses to retain heat. Too, sometimes you will find the iguanas on a sandy beach or in the mangrove trees, depending on the island on which they live.

Photo from Galapagos Conservancy of Marine Iguanas covered with crusted salt

A really intriguing feature about marine iguanas is that sometimes they look as though their heads are lighter in color than their bodies — sometimes white almost as though they are wearing a wig. But, they aren’t white. This is just the result of their desalination process and is a crust of salt on the iguana’s head. When diving in the ocean, the iguanas inevitably swallow undigestible salt water. They have developed special glands between their eyes and nostrils that collect and remove the salt. They shoot it out in a spray — like sneezing. Sometimes — in fact, often — the spray lands right back on the iguana’s own head covering him in a white mist. This is just another example of an adaption that has evolved to enable these descendants of terrestrial ancestors to live in salt water.

A fight ensues

Like many other species, marine iguanas live in large colonies and the males become territorial and combative during breeding season in February and March. The males who are vying for territory and mating privileges engage in very intense combat, with head butting, pushing, shoving and locking of the crests on top of their heads.

The loser retreats

The fighting can last up to five hours. For all this intensity, the loser leaves. sometimes with an injury, and the victor gets the girl! But she doesn’t hang around, rather hightails it away as quickly as possible.

A juvenile marine iguana on Isabela Island photo by Kimber Wukitsch; photo from

After a five-week gestation period, she lays her eggs in a soft sandy nest that she has dug and the babies are born in May and June. Baby iguanas are tiny, and weigh just 1 ½ to 2 ½ ounces and are only about 6 inches long. It takes a hatchling about two years to develop the strength to swim. Iguanas are a protected species in the Galapagos Islands. The Galapagos Marine Iguana is considered vulnerable in the International Union for Conservation of Nature Red List of Endangered Species. The Galapagos National Park Service has created artificial nesting sites on some of the smaller islands away from predators in order to preserve the iguana population.

Whether classified as land or marine, iguanas are strange, fascinating and unusual. We have to do everything in our power to protect this fabulous example of adaptation and evolution.

Harry Jiménez, Owner and General Manager 
 Galapagos Eco Friendly
 Av. 12 de Febrero y Av. J Roldo
 San Cristobal Island
 Galapagos, Ecuador SCY
 Reservations: 593 052 520 124

A version of this article has been published at