Black Spiny-tailed Iguana

Black Spiny-tailed Iguana, Ctenoaura similis

Black Spiny-tailed Iguana, Ctenoaura similis. Photographs taken in Cancún, Quintana Roo, March 2021. Photographs and identifications courtesy of Marina Sutormina, Stockholm, Sweden.

Black Spiny-tailed Iguana, Ctenoaura similis. Photograph taken in Mazatlán, Sinaloa, April 2024. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California. Identification courtesy of Bob Hillis, Ivins, Utah.

The Black Spiny-tailed Iguana, Ctenosaura similis, is a member of the Iguanidae family of Iguana and Chuckwalla Lizards. The Iguanidae family consists of seven hundred members placed in forty genera. There are fifteen global species in the Ctenosaura genus. They are also commonly referred to as the Black Iguana due to the distinctive black rows of sharp, curved spines that ring their long tails. The Black Spiny-tailed Iguana is known in Mexico as Garrobo Del Noreste.

Black Spiny-tailed Iguanas are large and bulky in stature. They vary in color but are typically various shades of whitish gray or tan with a series of four to twelve well-defined dark dorsal bands that extend to the ventral scales. The males develop an orange color around their head and throat during breeding season with tinges of blue and peach on their jowls. The juveniles are olive-green with brown markings and become grayish as they mature. They have a crest of short spines that extend down the center of their back and their tail length is similar to their body length. They display sexual dimorphism with males possessing a well-developed dorsal crest and small dewlaps under their throat. Conversely, females do not have a dorsal crest. In addition, males are capable of growing up to 1.3 meters (4 feet 3 inches) in length while females are slightly shorter at 80 cm (2 feet 7 inches) to  to 1 meter (3 feet 3 inches) in length. The Black Spiny-Tailed Iguana is the largest species in their genus and average 1 kg (2 lbs 3 oz) in weight, but some individuals can get much larger.

Black Spiny-tailed Iguanas are highly gregarious and territorial, living in colonies dominated by one male. Territorial displays include color changes, body inflation, jaw-gaping, “push-ups” or rapid nodding of the head, and sometimes biting and tail thrashing battles. Combat often occurs for attaining or defending a territory or a mate. Despite their size, the Black Spiny-Tailed Iguana can move quickly and has been reported to be the world’s fastest lizard with speeds up to 34.6 km per hour (21.5 mph). They utilize their speed, tail spines, and bite as defense mechanisms to avoid predation. They are skilled diggers and have excellent climbing abilities, preferring rocky habitats with numerous crevices for hiding, rocks to bask on, and nearby trees to climb.

Black Spiny-tailed Iguanas are primarily herbivorous and consume flowers, fruit, leaves, and stems. Occasionally, they will consume arthropods, birds, eggs, fish, rodents, and sea turtle hatchlings. The juveniles primarily consume insects. They are known to eat the fruit of the Manchineel Tree which is poisonous to most other animals. In addition, they will sometimes  eat their own eggs and practice cannibalism on their young. In turn, they are preyed upon by numerous snake species. Mating occurs in the spring, during the dry season, via internal fertilization. Males show dominance and interest by head bobbing and eventually, the male will chase the female until he can catch and subdue her. Females dig burrows approximately 50 cm  (1 foot 7 inches) deep and lay between 12 to 88 eggs in the nest. The eggs hatch in 90 days, just before the wet season, and the hatchlings dig their way out of the sand. Juveniles have a low survival rate, suffering from a lack of food and predation by hawks and owls. Once they reach maturity, they have excellent survival rates with life spans of up to twenty-three years in captivity and nine years in the wild.

The Black Spiny-tailed Iguanas are found along the coast from Tabasco eastward around the Yucatán Peninsula, south to Belize in the Atlantic  and from Oaxaca south to Guatemala in the Pacific. They can be found in lowland scrub, woodland, grassland, and beach dunes at elevations up to 900 meters (2,950 feet). They can quickly adapt to new environments and are often found in close proximity to humans.

The Black Spiny-tailed Iguana is very similar to and easily confused with the Mexican Spiny-Tailed Iguana or la inguana negra, Ctenosaura pectinata (lacks dark dorsal crossbands).

From a conservation perspective, the Black Spiny-tailed Iguana is currently considered to be of Least Concern with expanding, widely-distributed populations. They are raised for human consumption throughout Central America. Their consumption is believed to have positive medicinal value imparting strength and curing impotence. They are also utilized at a low level by the Pet Trade. They are also found in botanical gardens and zoos in locations that have year-round warm climates.

The Black Spiny-tailed Iguana is highly invasive and in some areas they are considered to be pests. They have been introduced in many areas via terrarium releases and known to hitchhike on cargo ships. Due to their large clutch size they have the ability to quickly expand and form large, established populations. They are know to consume valuable horticultural plants, threaten native species through predation and usurpation of burrows and invade dwellings. In some areas they are targets of eradication programs that include trapping and shooting. The Black Spiny-tailed Iguana has been implicated in the demise of the threatened Gopher Tortoise, Gopherum polyphemus.