Though all boids are constrictors, only this species is properly referred to as "Boa constrictor"; a rare instance of an animal having the same common and scientific binomial name. (The distinction is shared with Tyrannosaurus rex.)
All subspecies are referred to as "Boa constrictors", while the nominate subspecies, B. c. constrictor, is often referred to specifically as the "red-tailed boa". Within the exotic pet trade it is also known as a "BCC", an abbreviation of its scientific name, to distinguish it from other Boa constrictor subspecies such as the Boa constrictor imperator which is also regularly, and erroneously, referred to as a "red-tailed boa" or "common boa".
Other common names include "chij-chan" (Mayan), "jibóia" (Latin American) and "macajuel" (Trinidadian).
The Boa constrictor is a large snake, although only modestly sized in comparison to other large snakes such as the reticulated python and Burmese python, and can reach lengths of anywhere from 1–4 meters (3–13 feet) depending on the locality and the availability of suitable prey. There is clear sexual dimorphism seen in the species, with females generally being larger in both length and girth than males. As such, the average size of a mature female boa is between 7–10 ft, whilst it is 6–8 ft for the males. It is common for female individuals to exceed 10 ft, particularly in captivity, where lengths of up to 12 ft or even 14 ft can be seen. A report of a Boa constrictor growing up to 18½ ft (5.5 m) was later found to be a misidentified green anaconda.
The Boa constrictor is a heavy-bodied snake, and large specimens can weigh up to 27 kg (60Ibs).
The size and weight of a Boa constrictor depends on subspecies, locale, and the availability of suitable prey. Several populations of Boa constrictors are known as "dwarf boas", such as the population of B. c. imperator on Hog Island. These smaller subspecies are generally insular populations. B. c. constrictor itself reaches, and occasionally tops, the averages given above, as it is one of the relatively large subspecies of Boa constrictor.
Other examples of sexual dimorphism in the species include the fact that males generally have longer tails to contain the hemipenes and also longer pelvic spurs, which are used to grip and stimulate the female during copulation. Pelvic spurs are the only external sign of the rudimentary hind legs and pelvis, seen in all boas and pythons.
The coloring of Boa constrictors can vary greatly depending on the locality. However, they are generally a brown, grey or cream base color, patterned with brown or reddish brown "saddles" that become more pronounced towards the tail. It is this coloring that gives Boa constrictor constrictor the common name of "red-tailed boa", as it typically has more red saddles than other boa constrictor subspecies. The coloring works as very effective camouflage in the jungles and forests of its natural range.
There are also individuals that exhibit pigmentary disorders such as albinism. Although these individuals are rare in the wild, they are common in captivity where they are often selectively bred to make a variety of different color "morphs". Boa constrictors have an arrow-shaped head that has very distinctive stripes on it. One runs dorsally from the snout to the back of the head. The others run from the snout to the eyes and then from the eyes to the jaw.
Boa constrictors can sense heat via cells in their lips, though they lack the labial pits surrounding these receptors seen in many members of the boidae family. Boa constrictors also have two lungs, a smaller (non-functional) left and enlarged (functional) right lung to better fit their elongated shape, unlike many colubrid snakes which have completely lost the left lung.
