Geographic Range Boa constrictor is an exclusively New World species which has the largest distribution of all neotropical boas. Boa constrictors range from northern Mexico south through Central and South America. In South America the range splits along the Andes mountains. To the east of the Andes, B. constrictor is found as far south as northern Argentina. On the west side of the mountains, the range extends into Peru. Boa constrictors are also found on numerous islands off the Pacific coast and in the Caribbean. Islands included in the boa constrictor range are: the Lesser Antilles, Trinidad, Tobago, Dominica, and St. Lucia. Some islands off the coast of Belize and Honduras are also inhabited by this species. (Chiaraviglio, et al., 2003; Mattison, 2007; O'Shea, 2007; Stafford, 1986) Biogeographic Regions

nearctic native

neotropical native



Physical Description Boa constrictor has long been famous as one of the largest species of snake. In reality, boa constrictors are fairly modest-sized boids and are dwarfed by the other competitors for this title. The maximum length reported in B. constrictor was slightly over 4 meters. Individuals are generally between 2 and 3 meters in length, although island forms are commonly below 2 meters. Within populations, females are usually larger than males. However, the tails of males may be proportionally longer than those of females because of the space taken up by the hemipenes. Boa constrictor coloration and pattern are distinctive. Dorsally the background color is cream or brown that is marked with dark "saddle-shaped" bands. These saddles become more colorful and prominent towards the tail, often becoming reddish brown with either black or cream edging. Along the sides, there are rhomboid, dark marks. They may have smaller dark spots over the entire body. The head of a boa constrictor has 3 distinctive stripes. First is a line that runs dorsally from the snout to the back of the head. Second, there is a dark triangle between the snout and the eye. Third, this dark triangle is continued behind the eye, where it slants downward towards the jaw. However, there are many variations on appearance. At least 9 subspecies are currently recognized by some authorities, although many of these are poorly defined and future research will undoubtedly modify this taxonomy. Currently acknowledged subspecies include: B. c. constrictor, B. c. orophias, B. c. imperator, B. c. occidentalis, B. c. ortonii, B. c. sabogae, B. c. amarali, B. c. nebulosa (Dominican boa, recently elevated to full species), and B. c. longicauda. Most of these subspecies are distinguished largely by their range rather than appearance, but regional (subspecific) variation in form, size, and coloration does occur. (Chiaraviglio, et al., 2003; Mattison, 2007; O'Shea, 2007; Stafford, 1986) As in most members of the family Boidae, boa constrictors possesses pelvic spurs. These are hind leg remnants found on either side of the cloacal opening. They are used by males in courtship and are larger in males than in females. Males possess hemipenes, a double-penis, of which only one side is commonly used in mating. Although heat-sensing pits are common in Boidae, they are absent in B. constrictor. Thus, this species is presumed to have no specialized thermosensory abilities. The teeth of boa constrictors are aglyphous, meaning they do not possess any elongated fangs. Instead, they have rows of long, recurved teeth of about the same size. Teeth are continuously replaced; particular teeth being replaced at any one time alternate, so that a snake never loses the ability to bite in any part of its mouth. Boas are non-venomous. Boa constrictors have two functional lungs, a condition found in boas and pythons. Most snakes have a reduced left lung and an extended right lung, to better match their elongated body shape. (Mattison, 2007; O'Shea, 2007; Pough, et al., 2004) Other Physical Features

heterothermic

polymorphic Sexual Dimorphism

female larger Range length 1 to 4 m 3.28 to 13.12 ft

Average length 2-3 m ft

Development Fertilization is internal, with mating facilitated by the pelvic spurs of males. Boa constrictors are ovoviviparous; embryos develop within their mothers' bodies. Young are born live and are independent soon after birth. Newborn boa constrictors resemble their parents and do not undergo any metamorphosis. As in other snakes, boa constrictors shed their skins periodically as they age, allowing them to grow and preventing the scales from becoming worn. As a boa grows, and its skin is shed, its coloration may gradually change. Young snakes tend to have brighter colors and more contrast between colors, but most changes are subtle. (Mattison, 2007; O'Shea, 2007; Pough, et al., 2004; Stafford, 1986)

Lifespan/Longevity Boa constrictors are potentially long-lived, perhaps averaging around 20 years old. Captive boas tend to live longer than wild ones, sometimes by as much as 10 to 15 years. (O'Shea, 2007; Stafford, 1986) Range lifespan

Status: wild 30 (high) years

Range lifespan

Status: captivity 40 (high) years

Average lifespan

Status: wild 20 years

Typical lifespan

Status: captivity 25 to 35 years

Food Habits Boa constrictors are carnivorous generalists. The main bulk of their diet consists of small mammals, including bats, and birds. However, they will eat any animal they can capture and fit in their mouths. Boa constrictors capture prey through ambush hunting, although occasionally they actively hunt. They can rapidly strike at an animal that passes by a branch that they are suspended from, for example. They are non-venomous and prey is dispatched through constriction. Boa constrictors wrap their prey in the coils of their body and squeeze until the prey asphyxiates. This is especially effective against mammals and birds whose warm-blooded metabolism demands oxygen at a rapid rate. Once dead, the prey is swallowed whole. Interestingly, if captive boa constrictors are presented with dead prey, they still constrict the food item before consuming it. It takes boa constrictors 4 to 6 days to fully digest a meal. (Bartlett and Bartlett, 2003; Mattison, 2007; O'Shea, 2007; Stone and Holtzman, 1996) Primary Diet

carnivore eats terrestrial vertebrates

Animal Foods

birds

mammals

amphibians

reptiles

eggs

Predation When threatened, boa constrictors will bite to defend themselves. Though there are few references to predation on boa constrictors in nature, they are certainly killed and consumed by numerous reptilian, avian, and mammalian predators. Young boas are especially vulnerable. (O'Shea, 2007; Pough, et al., 2004) Anti-predator Adaptations

cryptic

Ecosystem Roles Boa constrictors are predators on birds and small mammals, including bats. They are important predators of rodents and opossums, especially, which can become pests in some areas and carry human diseases. (Mattison, 2007; O'Shea, 2007; Stone and Holtzman, 1996)

Economic Importance for Humans: Positive Boa constrictors are popular in the pet trade. It is easy to obtain boa constrictors that have been captive bred for generations, increasing their affinity for humans. They are relatively undemanding pets, as long as their large adult size and space needs are accounted for. Proper levels of heat and humidity (boas usually need a dry climate, otherwise their scales will develop rot) need to be observed. Boa constrictors can be fed dead mice and rats and only require food and defecate about once a week. Proper care should be observed in handling them, especially the larger varieties. Boa constrictors, whole or in parts, are also seen in local markets within their range, presumably as food or medicine. They are sometimes harvested for the skin trade. In some areas boas constrictors can play a large role in controlling populations of pest rodents and opossums (Didelphidae). Opossums in the tropics can be carriers for the human disease leishmaniasis, which is transferred by blood-feeding sand flies (Psychodidae) that parasitize the opossums. Boa constrictor predation pressure may help to regulate opossum populations and decrease potential trasmission of leishmaniasis to humans. (Bartlett and Bartlett, 2003; Mattison, 2007; O'Shea, 2007) Positive Impacts

pet trade

food

body parts are source of valuable material

controls pest population

Economic Importance for Humans: Negative Little negative impact on humans is known. Boa constrictors rarely, if ever, attack humans except in self-defense. Humans, even children, are far outside the range of prey size taken by boas. Boa constrictor bites are painful bure are unlikely to be dangerous as long as standard medical care is obtained. Boa constrictors are not venomous. Large captive snakes must always be handled with extreme care, especially when being fed, as a hungry snake strikes and constricts in a largely automatic sequence of behaviors. Very large snakes should handled and fed only with more than one person present. (Bartlett and Bartlett, 2003; Mattison, 2007; O'Shea, 2007) Negative Impacts

injures humans bites or stings



Conservation Status Overcollection for the pet trade and needless direct persecution has had an impact on some B. constrictor populations. Some populations have been hit harder than other, and various wild populations are now endangered, particularly those on offshore islands. On the mainland, boa constrictors have been harvested for their skins, meat and body parts. Furthermore, habitat loss and road mortality has reduced populations. Most boa constrictors are on the CITES Appendix 2 list. The subspecies B. c. occidentalis is on Appendix 1 of CITES. (O'Shea, 2007; Pough, et al., 2004) IUCN Red List Not Evaluated

US Federal List No special status

CITES Appendix I Appendix II

State of Michigan List No special status

As mentioned above, the species Boa constrictor is divided into many subspecies. These subspecies are highly variable and over the years the taxonomy has changed. Currently there are at least 9 recognized subspecies: Colombian or common boa constrictors (B. c. constrictor), St. Lucia boa constrictors (B. c. orophias), Imperial or Central American boa constrictors (B.c. imperator), Argentine boa constrictors (B.c. occidentalis), Peruvian boa constrictors (B.c. ortonii), Taboga Island boa constrictors (B.c. sabogae), Bolivian boa constrictors (B.c. amavali), Dominican or clouded boa constrictors (sometimes considered a full species, B.c. nebulosa), and long-tailed boa constrictors (B.c. longicauda). Subspecies that are occasionally cited, but are not as widely acknowledged or are often combined with a previously listed subspecies are: Mexican boa constrictors (B.c. mexicana), black-bellied boa constrictors (B.c. melanogaster), and Tres Marias Islands boa constrictors (B.c. sigma). As apparent by the names, most subspecies are recognized by their range. In many cases, a boa constrictor of unknown geographical origin may be impossible to assign to a subspecies. Additionally, pet trade breeders have created many new color morphs that are not seen in wild populations. (Andrade and Abe, 1998; Bartlett and Bartlett, 2003; Mattison, 2007; O'Shea, 2007; Stafford, 1986)

Contributors Tanya Dewey (editor), Animal Diversity Web. Laurel Lindemann (author), Michigan State University, James Harding (editor, instructor), Michigan State University.

Glossary Nearctic living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico. Neotropical living in the southern part of the New World. In other words, Central and South America. acoustic uses sound to communicate agricultural living in landscapes dominated by human agriculture. arboreal Referring to an animal that lives in trees; tree-climbing. carnivore an animal that mainly eats meat chaparral Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo. chemical uses smells or other chemicals to communicate crepuscular active at dawn and dusk cryptic having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect. fertilization union of egg and spermatozoan food A substance that provides both nutrients and energy to a living thing. forest forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality. heterothermic having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature. iteroparous offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes). native range the area in which the animal is naturally found, the region in which it is endemic. nocturnal active during the night pet trade the business of buying and selling animals for people to keep in their homes as pets. polygynandrous the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females. polymorphic "many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph. rainforest rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal. riparian Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream). scrub forest scrub forests develop in areas that experience dry seasons. seasonal breeding breeding is confined to a particular season sedentary remains in the same area sexual reproduction that includes combining the genetic contribution of two individuals, a male and a female solitary lives alone tactile uses touch to communicate terrestrial Living on the ground. territorial defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement tropical the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south. tropical savanna and grassland A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia. savanna A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome. temperate grassland A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands. vibrations movements of a hard surface that are produced by animals as signals to others visual uses sight to communicate viviparous reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.