Classification and Range
The boa constrictor belongs to the family Boidae, which includes seven genera of boas, four genera of sand boas, and eight genera of pythons. Though some of the 64 species in the family are less than 3.3 feet (1 m) in length, others are the largest snakes in the world; a green anaconda was recorded as being 37 feet (11.3 m) long! Boa constrictor ranges through much of Central and South America, from Mexico to Argentina, and to the Lesser Antilles and other islands.
Boa constrictors live from sea level to 3,300 feet (1,000 m) elevation, in tropical rainforests, semi-deserts, rocky hillsides, savannas, and near cultivated fields and homes. They climb well, and those in forests may spend a lot of time in trees. Though boa constrictors can swim, most don’t spend significant time in water. During winter, in cooler parts of their range, they may become somewhat torpid, without being completely inactive.
Common boas are thick-bodied snakes that can be 3-14 feet (.9-4.3 m) long and can weigh more than 100 pounds (45 kg). Most mature at 5-8 feet (1.5-2.4 m) long and weigh less than 60 pounds (27 kg). They have oval, diamond, or bat-shaped patterns of reddish-brown outlined in black, on a background of cream, pale tan or gray. “Red-tailed boas”aren't another species, but a color variation found in both the Boa constrictor constrictor and B. c. imperator subspecies. Their relatively short tails are prehensile and able to securely grip branches. They have many small teeth for gripping their prey, but no fangs or venom. A boa kills by suffocation, tightening its coils when a captured animal exhales and preventing it from inhaling. Boas have spurs near the cloacal opening that are vestiges of the legs possessed by ancestors. In females, the spurs are usually smaller or less hooked, and may be invisible or absent.
One of the longest-lived of snakes, boa constrictors live 20 years or more in captivity. At the Philadelphia Zoological Park one lived 40 years.
In the wild: They take a variety of prey that includes lizards, birds, rodents, monkeys and even wild pigs At the zoo: Keepers offer the boa constrictors one large rat per week
Common boas are ovo-viviparous, which means the female retains her eggs internally until they hatch, so she bears live young. Most clutches number 20-50 thin-membraned eggs; the record is 77, at the zoo in Quebec. The neonates are born after 100-150 days of development. Females can store sperm for quite some time before fertilization takes place, so the total apparent gestation can take 10 months. The female will usually eat little or nothing while she is retaining eggs (called gravid in reptiles).
Boa constrictors are 17-20 inches (43-51 cm) long at birth, and can grow to 3 feet (.9 m) in several months. They reach sexual maturity at 3-4 years age, when the larger ones are over 6 feet (1.8 m) long. Except during the rainy season, when they breed, they're solitary. In captivity a male might court a female for up to five weeks before copulation occurs. Courting consists of winding back and forth over the female's body and stimulating her cloaca with his spurs.
Many a Name
Taxonomists divide the rather variable species Boa constrictor into several subspecies, though not as many as they used to. For example, B. c. imperator (a subspecies found from Mexico to Colombia) now includes the boas once called B. c. eques ( from Payta, Peru) and B. c. isthmica ( from del Darien, Panama), along with others. When biologists compared many individuals from these localities they didn't differ consistently from animals in the larger population.
Some other currently accepted subspecies are B. c. constrictor (from the northern Amazon basin), B. c. amarali ( from the southern Amazon basin), B. c. occidentalis (from Paraguay and Argentina), and B. c. nebulosa (from Dominica). Unofficial names made up by animal dealers, such as Guyana red-tailed, may not describe all the boas in Guyana, but they can guide pet buyers in getting a desired color of snake from a reputable breeder.
Location at the Zoo
The common boas at Woodland Park Zoo are kept off-exhibit and used in educational programs. Other species of boids are found at the Day Exhibit, Tropical Rain Forest and Trail of Vines. You may have to look carefully to find these well-camouflaged snakes
Boa constrictors are not an endangered species. The number of boa constrictors in the wild is not well-known, but they have become very rare in some parts of their range. Exportation for the pet trade lowers the numbers of certain desirable reptile populations to the point where they may become extinct in the wild. Boa constrictors, and all reptiles, play an important role in nature's web of life. Habitat destruction and hunting for skins to make tourist products or souvenirs contribute to the decline of reptiles worldwide. Each of us needs to take action to protect wild habitats, so snakes and all animals can continue to play their vital roles in maintaining the delicate balance of nature.
We need snakes! A few of the many benefits they provide are:
•Snakes eat insects and rodents that eat our crops or spread disease. By helping to control populations of these rapidly breeding animals, snakes keep at levels where natural habitats can support them. •Snake venom is used in medical research on blood clotting and anesthetics and to make some medicines.
Reptiles as Pets
We do not recommend reptiles as pets for most people as they require very specialized diets and environments. We also receive hundreds of requests each year to take former pet iguanas, boas and other reptiles but we cannot accept these due to space, health and unknown backgrounds. If you need to find a reptile or amphibian a new home, we suggest you contact a local herpetological group in your area.
In the Puget Sound region, contact the Pacific Northwest Herpetological Society as a resource. If you do choose to get a reptile as a pet, please learn as much as possible about their care and the best species before making your decision and never accept wild-caught animals as pets or release non-native reptiles or amphibians into the wild.
How You Can Help!
The effort to save endangered species requires cooperation and support at the regional, national and international levels. You can help in this cause. Join and become active in a conservation organization of your choice. Don't buy products made from wild animal parts. Anyone interested in owning a reptile should learn about its needs and be sure it was captive bred. Many more wild-caught animals die than ever reach pet stores, and those that are fortunate enough to survive are often stressed, malnourished and untamable. Read more about keeping a pet reptile at: http://www.kingsnake.com/ballpythonguide/pets.htm.
To learn other ways you can help, contact Woodland Park Zoo at firstname.lastname@example.org about supporting conservation programs at the zoo. Discover more about snakes by contacting the Society for the Study of Amphibians and Reptiles at 303 W. 39th St., PO Box 626, Hays, KS 67601, or the American Federation of Herpetoculture: AFH, P.O. Box 300067, Escondido, CA, 92030-0067. Learn other ways you can help conserve wildlife and habitats by visiting our How You Can Help page.
Sources and Suggested Reading
Halliday, Tim, and Adler, Kraig, eds. 1986. The Encyclopedia of Reptiles and Amphibians. Facts on File, Inc., New York, NY.
Bauchot, Roland, ed. 1994. Snakes: A Natural History. Sterling Publishing Co, Inc, New York. 220 p.
Wagner, Doug. 1996. Boas: A Complete Pet Owner's Manual. Barron's Educational Series, Hauppauge, NY. 96 p.
McCarthy, Colin. 2000. Eyewitness: Reptile. Dorling Kindersley Publishing, London. 64 p.
Markle, Sandra. 1995. Outside and Inside Snakes. Simon & Schuster, New York. 40 p.
Burton, John A. 1991. The Book of Snakes. Quantum Books Ltd, London.