Interesting Creatures…The Boa Constrictor

Oct 30, 2011 Features / Columnists, Interesting Creatures in Guyana

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The Boa constrictor is a large, heavy-bodied species of snake. It is a member of the family Boidae found in North, Central, and South America, as well as some islands in the Caribbean. A staple of private collections and public displays, its colour pattern is highly variable yet distinctive. Ten subspecies are currently recognized, although some of these are controversial.
Though all boids are constrictors, only this species is properly referred to as “Boa constrictor”; an almost unique instance of an animal having the same common and scientific binomial name. 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”.
The Boa constrictor is a large snake, although only modestly sized in comparison to other large snakes such as the reticulated and Burmese python, and can reach lengths of anywhere from 1–4 metres (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.” 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 colouring of Boa constrictors can vary greatly depending on the locality. However, they are generally a brown, grey or cream base colour, patterned with brown or reddish brown “saddles” that become more pronounced towards the tail. It is this colouring 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 colouring 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 colour “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.
Boa constrictor flourishes in a wide variety of environmental conditions, from tropical rainforests to arid semi-desert 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 constrictor will also occupy the burrows of medium-sized mammals, where it can hide from potential predators.
Boa constrictors are solitary animals, and will only associate with conspecifics to mate. They are nocturnal, however they may bask during the day when night-time temperatures are too low. As semi-arboreal snakes, young boa constrictor individuals may climb into trees and shrubs to forage, however they become mostly terrestrial as they become older and heavier. Boa constrictors will strike when threatened, and will bite in defence. This bite can be painful, especially from large snakes, but is rarely dangerous. However, care must be taken to ensure that infection does not result from the injury.
Specimens from Central America are more irascible, hissing loudly and striking repeatedly when disturbed, while those from South America tame down more readily. Like all snakes, Boa constrictors that are in a shed cycle will be more unpredictable. This is because the substance that lubricates between the old skin and the new will make the eyes appear “milky” or “opaque”, and as such the snake cannot see very well. This will cause it to be more defensive than it may be otherwise.
Prey includes a wide variety of mammals and birds. The bulk of their diet consists of rodents, but larger lizards and mammals as big as ocelots are also reported to have been consumed. Young boa constrictors will eat small mice, birds, bats, lizards and amphibians. The size of the prey item will increase as they get older and larger.
Boa constrictors are ambush predators and as such will often lie in wait for an appropriate prey to come along at which point they will attack. However, they have also been known to actively hunt, particularly in regions with a low concentration of suitable prey, and this behaviour generally occurs at night.
The boa will first strike at the prey, grabbing it with its teeth, it then proceeds to constrict the prey until death before consuming it whole. Their teeth also help force the animal down the throat whilst muscles then move it towards the stomach. It will take the snake approximately 4–6 days to fully digest the food, depending on the size of the prey and the local temperature. After this the snake may not eat for anywhere from a week to several months, due to its slow metabolism.

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