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Boa constrictorBoa Constrictor

By Laurel Lindemann

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)

Habitat

Boa constrictors occupy a variety of habitats. Primary habitat is rainforest clearings or edges. However, they are also found in woodlands, grasslands, dry tropical forest, thorn scrub, and semi-desert. Boa constrictors are also common near human settlements and often found in agricultural areas. Boa constrictors are commonly seen in or along streams and rivers in appropriate habitats. Boa constrictors are semi-arboreal, although juveniles tend to be more arboreal than adults. They also move well on the ground and can be found occupying the burrows of medium-sized mammals. (Mattison, 2007; Montgomery and Rand, 1978; O'Shea, 2007; Stafford, 1986)

  • Aquatic Biomes
  • rivers and streams
  • Range elevation
    0 to 1,000 m
    0.00 to ft

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)

  • 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)

Reproduction

Males are polygynous; each male can mate with multiple females. Females may also have more than one mate in a season. Females are usually widely scattered and courting males must invest energy into locating them. Most female boa constrictors do not appear to reproduce annually. Usually about half of the female population is reproductive each year. Furthermore, females likely become reproductive only when they are in good physical condition. While a higher percentage of males seems to reproduce each year, it is likely that the majority of males also do not reproduce annually. (O'Shea, 2007; Stafford, 1986)

Boa constrictors generally breed during the dry season, usually from April to August, though the timing of the dry season varies across their range. Gestation lasts for 5 to 8 months depending on local temperatures. The average litter has 25 young but can be anywhere from 10 to 64 young. (Bertona and Chiaraviglio, 2003; Chiaraviglio, et al., 2003; Mattison, 2007; O'Shea, 2007; Stafford, 1986)

  • Breeding interval
    Females perhaps every other year, or less often, depending on condition.
  • Breeding season
    Breeding occurs during the dry season (April-August), birth occurs 5-8 months later.
  • Range number of offspring
    10 to 64
  • Average number of offspring
    24 (in <<B.c. occidentalis>>)
  • Range gestation period
    5 to 8 months
  • Average time to independence
    after only a few minutes
  • Average age at sexual or reproductive maturity (female)
    2-3 years
  • Average age at sexual or reproductive maturity (male)
    2-3 years

Maternal investment in young is considerable and requires the mother to be in good physical condition. Since young boa constrictors develop within the mother's body, they are able to develop in a thermoregulated, protected environment and they are provided with nutrients. Boa constrictor young are born fully developed and are independent within minutes of birth. Male reproductive investment is largely spent in finding mates. (Andrade and Abe, 1998; O'Shea, 2007; Stafford, 1986)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

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

Behavior

Boa constrictors are solitary, associating with conspecifics only to mate. However, Dominican populations which will occasionally den together. Boa constrictors are nocturnal or crepuscular, though they bask in the sun to warm themselves in cool weather. They periodically shed their skins (more frequently in juveniles than adults). A lubricating substance is produced under the old skin layer. When this occurs, the snake's eye can be seen to cloud up as this substance comes between its eye and the old eye-covering. The cloudiness affects their vision and boas will often become inactive for several days until the shedding has completed and their vision is restored. During shedding, the skin splits over the snout and eventually peels back from the rest of the body. Boa constrictors are most often observed in trees or on the ground near streams and rivers. (Bartlett and Bartlett, 2003; Chiaraviglio, et al., 2003; Montgomery and Rand, 1978; O'Shea, 2007; Stafford, 1986)

Home Range

Boa constrictors defend territories that change over time. Territories may be abandoned if resources or conditions decline. (O'Shea, 2007; Stafford, 1986)

Communication and Perception

Like most snakes, boa constrictors rely on strong vomeronasal senses. Their tongues flick continuously, bringing odor molecules into contact with the chemosensory (vomeronasal) organ in the top of their mouths. In this manner, they constantly sense chemical cues in their enviornment. Boa constrictors have good vision, even into the ultraviolet spectrum. In addition, they can detect both vibrations in the ground and sound vibrations through the air through their jaw bones. They do not have external ears. Unlike most boids, boa constrictors lack thermosensory pits. (Mattison, 2007; O'Shea, 2007; Sillman, et al., 2001; Stone and Holtzman, 1996)

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)

Other Comments

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.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

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.

References

Andrade, D., A. Abe. 1998. Abnormalities in a litter of Boa constrictor amarali. The Snake, 28: 28-32. Accessed December 05, 2008 at http://ns.rc.unesp.br/ib/zoologia/denis/boabnormal.PDF.

Bartlett, R., P. Bartlett. 2003. Red-tailed Boas and Relatives: Reptile Keeper's Guide. Hauppauge, NY: Barron's Educational Series, Inc..

Bertona, M., M. Chiaraviglio. 2003. Reproductive biology, mating aggregations, and sexual dimorphism of the argentine boa contrictor (Boa constrictor occidentalis). Journal of Herpetology, 37(3): 510-516. Accessed December 05, 2008 at http://www.bioone.org.proxy2.cl.msu.edu/perlserv/?request=get-document&issn=0022-1511&volume=37&page=510.

Chiaraviglio, M., M. Bertona, M. Sironi, S. Lucino. 2003. Intrapopulation variation in life history traits of Boa constrictor occidentalis in Argentina. Amphibia-Reptilia, 24/1: 65-74. Accessed November 07, 2008 at http://apps.isiknowledge.com.ezproxy1.ats.msu.edu/full_record.do?product=WOS&search_mode=GeneralSearch&qid=1&SID=1FBABe92cheDGF3aPf6&page=1&doc=2.

Mattison, C. 2007. The New Encylcopedia of Snakes. Princeton, New Jersey: Princeton University Press.

Montgomery, G., A. Rand. 1978. Movements, body-temperature and hunting strategy of a boa-constrictor. Copeia, 3: 532-533. Accessed November 07, 2008 at http://apps.isiknowledge.com.ezproxy1.ats.msu.edu/full_record.do?product=WOS&search_mode=GeneralSearch&qid=9&SID=1FBABe92cheDGF3aPf6&page=1&doc=1.

O'Shea, M. 2007. Boas and Pythons of the World. Princeton, New Jersey: Princeton University Press.

Pough, F., R. Andrews, J. Cadle, M. Crump, A. Savitzky, K. Wells. 2004. Herpetology, third edition. Upper Saddle River, NJ: Benjamin Cummings.

Sillman, A., J. Johnson, E. Loew. 2001. Retinal photoreceptors and visual pigments in Boa constrictor imperator. Journal of Experimental Zoology, 290(4): 359-365. Accessed December 05, 2008 at http://apps.isiknowledge.com.proxy2.cl.msu.edu/full_record.do?product=WOS&search_mode=GeneralSearch&qid=18&SID=3CdeLbP2E5edFCLGO8P&page=7&doc=70.

Stafford, P. 1986. Pythons and Boas. Neptune City, New Jersey: T.F.H. Publications, Inc. Ltd.

Stone, A., D. Holtzman. 1996. Feeding responses in young boa constrictors are mediated by the vomeronasal system. Animal Behavior, 52: 949-955. Accessed November 07, 2008 at http://apps.isiknowledge.com.ezproxy1.ats.msu.edu/full_record.do?product=WOS&search_mode=GeneralSearch&qid=11&SID=1FBABe92cheDGF3aPf6&page=1&doc=1.

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