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Ctenosaura similisBlack Iguana

By Emily Tran

Geographic Range

Ctenosaura similis is found throughout Mexico, large areas in Central America, and islands adjacent to Panama (Halliday and Adler 1992).

Habitat

These lizards are great diggers and baskers. They are found around ruins, stone walls, rocky open slopes and branches of large trees along the open borders of the forests. They generally live in dry, arid, open terrain. (Ervin 1992)

Physical Description

The ctenosaurs are large, bulky lizards with adult males reaching up to 18 inches long with a 18-inch tail. They are predominantly black but the dorsal surface may show black bands on a greyish background. Most have black mottling on their backs. The color may also lighten after basking in the sunlight with yellowish and orange markings becoming evident along the sides. Adult males and females are dimorphic. Adult males have well developed dorsal crests and small dewlaps. The dewlap, the crescent of skin that can be extended under the throat, is not inflated. A small bone bows out to extend the dewlap during times of threat, courtship, or while defending territory. Females lack obvious crests. There is considerable variation with age and sex and therefore identification may be difficult. The lizards have tails ringed with rows of sharp, curved spines, hence the name spiny-tailed iguana. The spines down the back are short. Juveniles tend to be olive-green becoming tan and then finally greyish as they grow (Grzimek 1990; Roberts and Roberts 1993; Cogger and Zweifel 1998).

  • Range mass
    0 to 0 kg
    0.00 to 0.00 lb
  • Average mass
    1 kg
    2.20 lb

Reproduction

This species becomes sexually mature at around 3 or 4 years of age. They congregate and mate during specific times of year that varies between populations. Male iguanas possess a pair of intromittent organs, the hemipenes. When not in use the hemipenes lie adjacent to the cloaca within the base of the tail.

During sexual activity one hemipenes is everted by the action of muscles and fills with blood. In copulation, which follows courtship behavior, only a single hemipenis is inserted into the female's cloaca, and the sperm travel along a groove in the hemipenis. Retraction of the hemipenis is accomplished by drainage of the blood sinuses and activation of retractor muscles that invert the structure as it is withdrawn.

In breeding season, the oviparous females then migrate to suitable areas to nest. After digging a burrow about half a meter deep, the female lays 2 to 25 eggs in the nest. She then defends the burrow for some time to prevent other females from nesting in the same spot. The young iguanas hatch 3 to 4 months later and then take about a week to dig their way out of the nest. These tiny iguanas can easily fit in the palm of a hand. If they survive the first difficult years of life, when food is often scarce and predators such as hawks and owls are dangers, these iguanas can live more than 60 years. (Whitfield 1984; Burton 1972; Halliday and Adler 1992)

Lifespan/Longevity

Behavior

This species can be belligerent, and may bite or wound an aggressor with their spines. More terrestrial than aboreal, they can run in a bipedal fashion. Highly gregarious and territorial, these iguanas live in colonies, ruled by a strict pecking order. One male in the colony is dominant, and although the other males hold territories, they will only defend them against one another and not against the leader. Territorial displays involve color changes, body inflation, jaw-gaping, "push-ups" or rapid nodding of the head, and sometimes, biting and tail thrashing battles. Larger males usually hold bigger and better territories and they mate more often. Combat often occurs when iguanas are attaining or defending a territory or a mate.

The male always courts, but he can only progress if his partner provides him with the right stimuli. She must respond by sexual stimuli, and like one of his own species; with a female of the wrong species his reproductive investments would result sterile hybrids, if any offspring at all. She must also signal that she is receptive-with mature ova ready for fertilization. Some of the visual signals that are often important in courtship are the males often bite, scratch, or lick females that have signalled their receptivity.

Juvenile iguanas often emerge together from the nest-hole, an anti-predator strategy in which many eyes are better than two and large numbers make individual capture less likely. Young iguanas often remain in groups with one of them temporarily behave as the leader. They engage in mutual tongue-licking and grooming, body and chin rubbing. At night they often sleep together on branches (Grzimek 1990; Whitfield 1984; Kaplan 2000; Bond 1998).

Food Habits

The ctenosaur is generally herbivorous, particularly on legume fruits, but is also known to have a diverse carnivorous diet that consist of small animals. Ctenosaurs have eaten rodents, bats, frogs, small birds, and a variety of insects. They have even been noted to eat eggs of their own young, and in one case, the tail of a juvenile was found inside an adult male, suggesting cannibalism. Youngsters are primarily insectivorous, switching into herbivorous habits as adults. (Murphy 1989; Roberts and Roberts 1993)

Economic Importance for Humans: Positive

The spiny-tailed iguana is edible and is a popular food for much of the rural population of Central America. In some areas, eating their flesh is considered potent "medicine", with the person deriving the iguana's strength after eating it. Also, the spiny-tailed iguanas are supposed to be a cure for impotence (Kaplan 2000).

Economic Importance for Humans: Negative

No documented example

Conservation Status

Man and his domestic animals are inevitably destroying the iguanas' environments and their species. The domestic animals such as cows devour most of the vegetation, which are the food sources for the iguanas. Their flesh is relished in many parts of the world but it is not overly exploited. In parts of South America iguanas are hunted by men imitating the screams of hawks. The iguanas' reaction to the cries is to "freeze" and they are then easily caught (Murphy 1989).

Contributors

Emily Tran (author), West Windsor-Plainsboro High School, Joan Rasmussen (editor), West Windsor-Plainsboro High School.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

native range

the area in which the animal is naturally found, the region in which it is endemic.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Bond, M. 1998. Accessed August 9, 2000 at http://costaricaherps.emconsulting.com/cteno.html.

Burton, M. 1972. The World Encyclopedia of Animals. New York: Thomas Y. Crowell Company.

Cogger, D., D. Zweifel. 1998. Encyclopedia of Reptiles & Amphibians: A Comprehensive Illustrated Guide. San Diego,CA: Weldon Owen Pty Limited.

Ervin, D. 1992. Accessed August 7,2000 at http://erasmus.biol.csufresno.edu/Ervin/gen-slds.html.

Grzimek, D. 1990. Animal Life Encyclopedia. New York: Litton World Trade Corporation.

Halliday, T., D. Adler. 1992. The Ecyclopedia of Reptiles and Amphibians. New York: Facts on File Inc..

Kaplan, M. 2000. Accessed August 10, 2000 at http://www.sonic.net/~melissk/cteno.html.

Murphy, R. 1989. The Larousse Encyclopedia of Animal Life. London: McGraw-Hill Book Company.

Roberts, M., M. Roberts. 1993. All About Iguanas. Neptune City, NJ: T.F.H Publications, Inc., Ltd..

Whitfield, D. 1984. MacMillan Illustrated Animal Encyclopedia. New York: MacMillan Publishing Company.

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