Description: The boa constrictor is a large snake, although it is only modestly sized in comparison to other large snakes, such as the reticulated python, Burmese python, or the occasionally sympatric green anaconda, and can reach lengths from 3 to 13 feet depending on the locality and the availability of suitable prey. Clear sexual dimorphism is seen in the species, with females generally being larger in both length and girth than males. The usual size of mature female boas is between 7 and 10 feet whereas males are between 6 and 8 feet. Females commonly exceed 10 feet, particularly in captivity, where lengths up to 12 feet or even 14 feet can be seen. The largest documented non-stretched dry skin is deposited at Zoologische Staatssammlung München and measures 14.6 feet without head. A report of a boa constrictor growing up to 18.5 feet was later found to be a misidentified green anaconda.
The coloring of boa constrictors can vary greatly depending on the locality. However, they are generally a brown, gray, or cream base color, patterned with brown or reddish-brown "saddles" that become more pronounced towards the tail. This coloring gives B. constrictor subspecies the common name of "red-tailed boas." The coloring works as a very effective camouflage in the jungles and forests of its natural range.
Habitat:B. constrictor flourishes in a wide variety of environmental conditions, from tropical rainforests to arid semidesert country. However, it prefers to live in rainforest due to the humidity and temperature, natural cover from predators, and vast amount of potential prey. It is commonly found in or along rivers and streams, as it is a very capable swimmer. Boa constrictors also occupy the burrows of medium-sized mammals, where they can hide from potential predators.
Range: Depending on the subspecies, Boa constrictor can be found through South America north of 35°S (Colombia, Ecuador, Peru, Venezuela, Trinidad and Tobago, Guyana, Suriname, French Guiana, Brazil, Bolivia, Uruguay, and Argentina), and many other islands along the coasts of South America. An introduced population exists in extreme southern Florida, and a small population on St. Croix in the U.S. Virgin Islands now appears to be reproducing in the wild.
Diet: Their prey includes a wide variety of small to medium-sized mammals and birds. The bulk of their diet consists of rodents, but larger lizards and mammals as big as monkeys, wild pigs and ocelots are also reported to have been consumed. Young boa constrictors eat small mice, birds, bats, lizards, and amphibians. The size of the prey item increases as they get older and larger.
Reproduction: Boa constrictors are viviparous, giving birth to live young. They generally breed in the dry season—between April and August—and are polygynous; thus, males may mate with multiple females. Half of all females breed in a given year, and a larger percentage of males actively attempt to locate a mate. Due to their polygynous nature, many of these males will be unsuccessful. As such, female boas in inadequate physical condition are unlikely to attempt to mate, or to produce viable young if they do mate. Reproduction in boas is almost exclusively sexual.
During the breeding season, the female boa constrictor emits pheromones from her cloaca to attract males, which may then wrestle to select one to breed with her. During breeding, the male curls his tail around the female's and the hemipenes (or male reproductive organs) are inserted. Copulation can last from a few minutes to several hours and may occur several times over a period of a few weeks. After this period, ovulation may not occur immediately, but the female can hold the sperm inside her for up to one year. When the female ovulates, a midbody swell can be noticed that appears similar to the snake having eaten a large meal. The female then sheds two to three weeks after ovulation, in what is known as a post-ovulation shed which lasts another 2–3 weeks, which is longer than a normal shed. The gestation period, which is counted from the postovulation shed, is around 100–120 days. The female then gives birth to young that average 15–20 inches in length. The litter size varies between females but can be between 10 and 65 young, with an average of 25, although some of the young may be stillborn or unfertilized eggs known as "slugs". The young are independent at birth and grow rapidly for the first few years, shedding regularly (once every one to two months). At 3–4 years, boa constrictors become sexually mature and reach the adult size of 6–10 feet, although they continue to grow at a slow rate for the rest of their lives. At this point, they shed less frequently, about every 2–4 months.
Status: Listed as Least Concern in view of its very wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The species is declining in some areas, but overall it is not threatened at present.
Disclaimer: ITIS taxonomy is based on the latest scientific consensus available, and is provided as a general reference source for interested parties. However, it is not a legal authority for statutory or regulatory purposes. While every effort has been made to provide the most reliable and up-to-date information available, ultimate legal requirements with respect to species are contained in provisions of treaties to which the United States is a party, wildlife statutes, regulations, and any applicable notices that have been published in the Federal Register. For further information on U.S. legal requirements with respect to protected taxa, please contact the U.S. Fish and Wildlife Service.
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