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 of anywhere from 3–13 feet depending on the locality and the availability of suitable prey.
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.
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.