Lee Richardson Zoo

Common Boa Constrictor

Order:  Squamata - snakes & lizards

Family:  Boidae - boas, pythons & anacondas

Scientific name:  Boa constrictor 


Description:  The boa constrictor is a long and limbless reptile.  It is tan, brown and black with large spots on its back and sides; tail may have reddish/orange tint to spots.  Head is flattened and blunted at the front with a dark stripe pattern continuing through the eye.  Boids have vestigial limbs in the form of tiny claws on either side of their vent.  This is what remains of their pelvic girdle.  Newborn boas range from 14 to 22 inches long and weigh between two and three ounces.  Depending on the subspecies, adult boas may range from 4 to 12 feet, and very rarely, up to 15 feet in length.  The longest boa on record is a red-tailed boa with a reported length of 18½ feet.  Few boa constrictors raised in captivity will exceed 60 pounds, with some races not exceeding 30 pounds.  They lack ears and eyelids, and have a soft, slender, black, harmless, forked tongue that is used for detecting smells.


Range:  Central and South America south into northern Argentina.


Habitat:  Occur in a wide range of habitats from semi-desert regions in Mexico to moist rain forests and anything in between.


Reproductive habits:  The boa constrictor is ovoviviparous, giving birth to live young.  Although no true placental connection between mother and young exists (as in mammals) there is a mechanism to allow exchange of oxygen and other necessary elements.  Sexual maturity is reached by the end of their third year.  Males recognize females by their anal secretions.  Copulation may last several hours.  The young develop inside the female in bubble like membranes.  Gestation lasts 3 to 5 months, with 8 to 60 young born.  Litter size increases with the age and size of the female.  The babies are delivered in their membranes, which dry up and break apart shortly after birth when the young begin to move around.  Live birth occurs in about one fourth of all snake species, and affords the young greater protection than those in eggs.  Because of the size and slow deliberate movements of boas, the extra bulk and weight added during pregnancy are of little consequence to the mother.  Snakes provide no parental care for their young, so high numbers of offspring per litter increase the chances of some individuals surviving.


Diet in WildPrimarily rodents, plus small mammals, lizards, frogs, birds and snakes.


Diet in ZooAdults are fed medium-sized rats; babies are fed killed adult mice.


General Info:  The Common boa is nonpoisonous.  Its skin and scales are smooth and dry to the touch, much like an orange peel.  Ectothermic (cold-blooded).  Boas are constricting snakes and kill their prey by suffocation, squeezing tightly to prevent breathing and circulation.  Prey is obtained by hiding and waiting, or by very slowly pursuing nearby animals.  Prey size seldom exceeds the snake’s girth.  A rapid strike catches the prey in the snake’s sharp tiny teeth.  Fatal wounds are never inflicted with the teeth.  Once captured, the snake constricts the prey, continually tightening its grip until the animal suffocates and its body relaxes.  It is then repositioned and swallowed whole, head first.  Their teeth are not designed for chewing or biting.  They are rootless and can break off the jaw and regrow.

Snakes are good swimmers.  They are deaf but can feel vibrations.  Their eyesight is good, however, objects outside a ten-foot range may not be seen if motionless.  The eye is covered by a scale called a brille or spectacle that protects it from dirt.  This scale becomes blue or cloudy just before the snake sheds thus impairing eyesight.  The outside layer of skin is shed as the snake grows.  Younger, more rapidly growing individuals may shed more frequently (5+ times per year) than older, slower growing snakes.  Snakes refrain from eating when eye scale is cloudy.

Unlike their giant relatives, the Burmese and reticulated pythons, common boas seldom grow large enough to become difficult to manage.  They are unable to swallow a human and no authenticated record of a human being killed by a boa has been found. 

However, all snakes, regardless of size, species or poisonous status, warrant respect, caution and common sense.  We recommend keeping one’s distance, avoiding contact and harassment, and contacting a knowledgeable source for questions or problems.  Generally, if given an escape route, snakes will flee rather than provoke a confrontation with a human.

Boids are found on every continent except Antarctica.  Generally, the boas are New World livebearers, while pythons are Old World egg layers.


PredatorsSmaller individuals are susceptible to raptors and other medium to large birds, and predatory mammals (canines and felines).



The General Care and Maintenance of Red-Tailed Boas.  1990. Philippe de Vosjoli. Advanced Vivarium Systems, Lakeside CA. 48 pp.

Living Snakes of the World.  1987 John M. Mehrtens.  Sterling Publishing Co., Inc.  New York. 480 pp.

Snakes of the World.  1986.  Christopher Mattison.  Facts on File Publications, New York.  190 pp.
Grzimek’s Animal Life Encyclopedia.   Vol. 6, Reptiles.  1975  Bernhard Brzimek. Van Nostrand Reinhold Co. New York.  589 pp.