The boa constrictor is a large snake, although it is only modestly sized in comparison to other large snakes, such as the reticulated python and Burmese python, and can reach lengths from 3–13 ft (0.91–3.96 m) depending on the locality and the availability of suitable prey.[5] Clear sexual dimorphism is seen in the species, with females generally being larger in both length and girth than males. As such, the usual size of mature female boas is between 7 and 10 ft (2.1 and 3.0 m), and 6 and 8 ft (1.8 and 2.4 m) for the males.[6] Females commonly exceed 10 ft (3.0 m), particularly in captivity, where lengths up to 12 ft (3.7 m) or even 14 ft (4.3 m) can be seen.[7] A report of a boa constrictor growing up to 18.5 ft (5.6 m) was later found to be a misidentified green anaconda.[8]
The boa constrictor is a heavy-bodied snake, and large specimens can weigh up to 27 kg (60 lb). Females, the larger sex, more commonly weigh 10 to 15 kg (22 to 33 lb).[9] Some specimens of this species can reach or possibly exceed 45 kg (100 lb), although this is not usual.[10]
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 reaches, and occasionally tops, the averages given above, as it is one of the relatively large subspecies of Boa constrictor.[6]
Other examples of sexual dimorphism in the species include males generally having longer tails to contain the hemipenes and also longer pelvic spurs, which are used to grip and stimulate the female during copulation.[11] Pelvic spurs are the only external sign of the rudimentary hind legs and pelvis, seen in all boas and pythons.
